References Materials for Chemical Analysis || General Application Fields

Reference Materials for Chemical Analysis Certification, Availability, and Proper Usage

Edited by Markus Stoeppler, Wayne R. WOK PeterJjenks

0 Wiley-VCH Verlag GmbH, 2001

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General Application Fields Edited by PeterJ Jenks

6.1 Workplace Air Monitoring

Yngvar Thomassen and Barry Tylee

6.1.1 Introduction

This Chapter provides information on available certified reference and quality control materials relevant for use in the measurement of airborne contaminants in occupational hygiene. The majority of measurements made in this area worldwide are solvents, dust (total, respirable), elements, oil mist, quartz, fiber identification (asbestos, man-made fibers), mists and gases.

Many proficiency testing schemes operate in the area of occupational hygiene measurements. Most countries organize their own schemes and there are differences between these schemes at many levels. Some organizers, for example the Workplace Analysis Scheme for Proficiency (WASP), and Proficiency Analytical Testing (PAT), managed by the Health and Safety Laboratory, Sheffield, UIC and National Institute for Occupational Safety and Health, Cincinnati, USA, respectively, prepare their samples simply by analyte spiking of, e.g. air filters with solutions. In several countries specialist facilities are available to produce samples with characteristics that are more realistic representations of the condition and complexities of true samples. These samples are more difficult to analyze than the original standards which proficiency testing schemes send to participants since they contain interferences and complex matrices that do not exist in samples prepared from solutions of pure standards. The demand for such material on a national scale is smaller than the alternative complements because these samples are specialized and designed to mimic those taken from specific atmospheres. Since these samples are also considered much more expensive to produce, the commercialization has been difficult, although the technology does exist for their production.

Surprisingly, few certified reference materials or quality control materials for use in the measurement of airborne contaminants are commercially available from world-wide producers. The main reason for the scarcity of such materials is related to great difficulties in producing realistic samples and the lack of interest from

I 197 G. 7 Workplace Air Monitoring

potential users. Even though, some materials are available for the most commonly occurring contaminants in workroom atmospheres.

6.1.2 Solvents

Facilities for the preparation of replicate samples from standard atmospheres exist in several countries. Two major institutes; the Vlaamse Installing voor Technolo- gisch Onderzoek in Belgium (Goelen et al. 1992) and the Netherlands Met Institute Van Swindon Laboratory in Netherlands (Hafkenscheid and Mower 1996) both have state of the art facilities that have been used for the production of reference material on behalf of the Standards, Measurements and Testing Programme of the European Commission (SM&T, formerly BCR). These systems can prepare gas phase mixtures at the occupational hygiene and environmental levels and obtain replicate samples with a high degree of accuracy and precision. The volatile organic compounds (VOCs) are injected continuously using methods such as heat/pressure differences etc. through a glass capillary into a manifold fed by a steam of purified air which is then sampled. The amounts of pollutants injected into the system can be calculated from gravimetric measurements and are directly traceable to primary standards (Goelen et al. 1992).

In Denmark, a similar system is used by Mi@-Kemi for commercial production of quality control samples for a number of different solvents and some inorganic gases; see Table 6.1.

Tab. 6.1 Reference materials for solvents and gases

Producer . Carrier Component(sJ

Milj@-Kemi, Charcoal tube

XAD2 tube

BCR

Na2C03 tube Chromosorb 106 Tenax tube OVS tube 2MP filter

HzS04

Benzene; t-Butanol, Heptane; 1-1-Dichloroethylene; Methoxypropanol, Toluene; Toluene Benzo(u)pyrene, Fluoranthene, Naphtalene; Halothane; Phenol Acetic acid Benzene, Vinyl acetate n-Butanol, n-Octane t-Butyl acrylate, Ethylene glycol-dimethacrylate Methylene diphenyl di-isocyanate (MDI) Ammonia

Glass fiber filters Formaldehyde-2,4-dinitrophenylhydrazone Tenax charged tube Charcoal charged tube

Benzene, Toluene, rn-Xylene Benzene, Toluene, rn-Xylene, o-Xylene

* Address: Miljer-Kemi, Smedeskowej $3, 8464 Galten, Denmark; www.miljo-ltemi.dk

198 G General Application Fields

6.1.3 Elements and Inorganic Compounds

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The Standards, Measurements and Testing Programme of the European Commis- sion launched a few years ago a project dealing with the development and, ultimately, the production of air filters realistically exposed to welding dust occurring during stainless steel welding (Christensen et al. 1999). This project resulted in the production and certification of a batch of 1100 filters for the Cr (VI) content (40.16 * 0.60 pg/g dust) (CRM 545). In addition, the total leachable Cr content ( 39.37 f 1.30 pg/g dust) was certified as a means to check for total Cr recovery.

Realistic loading ofthese filters was carried out using a multi-port sampler developed at NIOH in Oslo (Butler and Howe 1999). This sampling system basically consists of a thin circular aluminium drum which is evacuated by a large air pump. One face of the drum has up to 120 positions for air filter cassettes to be fitted. Each position is equipped with critical orifices to allow air to pass through them at a fmed rate during exposure. This sampling system is capable of producing near identical air fdter samples; at opti- mal conditions homogeneities better an I % RSD can be achieved.

Filter samples can be prepared to airborne workplace concentrations by spiking each fdter with aqueous solution containing elements with concentrations gravimetrically traceable to ultrapure metals or stoichiometrically well defined oxides. The amounts cor- respond for some of the materials to current threshold limit values of contaminants in workroom atmospheres provided that the simulated fdter has been exposed to one cubic meter of air. The certified values are based on a gravimetric procedure, i.e. weight per volume composition of the primary reference material dissolved in high purity sub-distilled acids. The National Institute of Occupational Health in Oslo, Norway, has produced several batches of such materials certified for 20 elements. Additionally, information values are reported for four other elements; see Table 6.2.

From NIST in the USA similar air filters spiked from solutions are also available for a number of elements. Although the element content of these filters is less representative for actual exposure levels in industrial settings, these samples are also of primary interest in the documentation of measurement uncertainties; see also Table 6.2.

Tab. 6.2 Elements on filter media, spiked from solution

Producer Material No.

NIOH, Oslo, B2 (pg) Norway"

A2 (M) NIST SRM 2676d (pglfilter)

SRM 2677a (p,g/filter) SRM 3087a (pg/filter)

Elements (levels) order of magnitude: pg or pg/filter

Al, As, B, Ba, Be, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Ni, Pb, Sb. Sn, Ti, TI, V, W, Zn, Zr (lower level) Same elements (approx. factor 2 higher level) Cd, Pb, Mn, Zn (three concentration levels) Be, As (three concentration levels) As, Ba, Cd, Cr, Fe, Mg, Mn, Ni, Pb, Se, V, Zn

* National Institute for Occup. Health (NIOH), P.O. Box 8149 DEP 0022 Oslo, Norway http://www.stami.no

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Quartz on filter media in a clay matrix is also available from NIST. The SRM 2679a is certified for quartz at three levels; 30.8, 80.2 and 202.7 pglfilter respectively. Respirable silica in powder form is also issued by NIST; SRMs 1878a and 1879a are crystalline silica materials with particles in the respirable range and they are intended for use in X-ray diffraction and infrared spectroscopy.

6.1.4 Asbestos

Optical microscope asbestos reference standards for use in identifying and quantify- ing asbestos types are available both from NIST and the Institute of Occupational Medicine (IOM) in Edinburgh, Scotland. The IOM materials consists of various asbestos materials; actinolite, amosite, anthophyllite, chrysotile (both from Cassiar, Canada and Zimbabwe), crocidolite and tremolite.

The NIST material SRM 1866a consists of a set of three common bulk mine- grade asbestos materials; chrysotile, amosite and crocidolite, and one glass filter sample. SRM 1867 consists of a set of three uncommon mine-grade asbestos materials; antophyllite, tremolite and actinolite. The optical properties of SRMs 1866a and 1867 have been characterized so that they may serve as primary calibration standards for the identification of asbestos types in building materials.

SRM 1868 consists of a set of two common bulk mine-grade asbestos materials; chrysotile and amosite, contained in matrices simulating building materials (calcium carbonate and glass fiber), in quantities at just below the U.S. EPA regulatory limit of I %. This material is certified by weight for the quantity of each asbestos material present.

SRM 1876b is intended for use in evaluating transmission electron microscopy (TEM) techniques used to identify and count chrysotile fibers. This SRM consists of sections of mixed-cellulose-ester filters containing chrysotile fibers deposited by an aerosol generator.

RM 8411 consists of a section of collapsed mixed-cellulose-ester filters with a high concentration (138 fiberslo.01 mm) of chrysotile and a medium concentration (43 fiberslo.01 mm) of amosite. It is intended for use in evaluating the technique used to identify and count asbestos fibers by TEM.

6.2 Clinical Application Fields Robert FM Herber andJan P Straub

6.2.1 Introduction

Reference materials have been long used in clinical chemistry; the first biological reference material was developed by Paul Ehrlich in 1897 (Buttner 1995). The routine use of RMs in clinical chemistry started in the early 1970’s and was driven by


the need for the testing of patient samples to give both reliable and comparable results. Physicians use data from the laboratory to help decide whether the patient has a certain disease, or not, and patients move from hospital to hospital.

The direct and immediate use of laboratory data in medical diagnostic decision making is unique, so the proper use of reference materials in conjunction proficiency testing clinical chemistry is vital if false and mis diagnosis is to be avoided.

A second reason for using reference materials in clinical chemistry is to ensure values obtained are traceable to those in a recognized, authoritative reference material (Johnson et al. 1996). As a result, the assignment of values of secondary and tertiary reference materials, calibrants, controls, and proficiency samples should be performed as precisely as possible (Johnson et al. 1996). Surprisingly there is still debate on this topic, and on the need for clinical chemistry to incorporate the princi- pals of analytical quality assurance (Dybkaer et al. 1999).

A number of international organizations are active in the field of clinical chemistry reference materials and proficiency testing, these include:

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the International Federation of Clinical Chemistry (IFCC) the International Union of Pure and Applied Chemistry (IUPAC) the World Health Organization (WHO) Various External Quality Assessment Working Groups

These and other organizations have published a number of papers on this subject, (Dybkaer and Stornng 1995; Heuck and Magrath 1995; McQueen et al. 1995; Wagner 1997). In the United States, the National Committee for Clinical Chemistry Laboratory Standardization (NCCLS) edits in the National Reference System for the Clinical Laboratory series of standards and guidelines on reference for assigning the best reference quality analytical and characteristic values. In one of the guidelines (NCCLS 1995). it has been stated, that CRMs must be produced under conditions specified by the Food and Drug Administration’s current Good Manufacturing Prac- tice Guidelines. In addition, the council of the National Reference System for the Clinical Laboratory (NRSCL) may accept the CRM produced on base of information of the institutions to serve as a source of the CRM, and the description of the CRM. This last issue must imply the CRM name, batch number, labelling and units; source of the material; homogeneity of the CRM samples; and certified materials.

Recent developments in Europe mean that reference materials included in diagnostic kits are covered by the recent directive controlling the production and use of in vitro diagnostic devices, and must be licensed before use.

As in other reference materials, a hierarchy exists with three levels (Johnson et al.

1996).

Primary reference materials, i.e. international or national certified reference materials, CRMs) Secondary reference materials, i.e. manufacturers’ in-house calibrants and controls (including commercial reference materials) Tertiary reference materials, i.e. controls and working calibrants produced by the user

I *01 G.2 Clinical Application Fields

At the end of 1996, a collaboration agreement was signed between the European Commission and the International Federation of Clinical Chemistry (IFCC) for the joint IRMM/IFCC production and certification of clinical reference materials.

The certification of a cortisol reference serum panel came to an end with the introduction of IRMM/IFCC-4yat the end of 1999. It consists of 34 sera (80-750 nmol/L) and has been certified using ID-GC/MS as a reference method.

Ongoing projects include the certification of enzyme CRMs for GGT, LD, ALAT, CIC-MB, ASAT, ALP and a-amylase at 37T, according to adapted IFCC methods. The first four materials (IRMM/IFCC-452, 453, 454, 455) are expected to be released during 2000. Projects on the certification of reference materials for cardiac marker (myoglobin) and total protein concentration in serum are under discussion. Even so the number of available CRMs for clinical chemistry and occupational toxicology is still limited. This has to do with the complexity of physiological compounds (e.g. proteins), the instability (e.g. enzymes), or the volatility (e.g. solvents).

In clinical chemistry, a great number of components are to be determined. These components may be classified according to their physiological function. In occupational toxicology, a division into functional chemical components may be a better classification.

In Tables (3.3 and 6.4 RMs of three major producers are mentioned, i.e. the World Health Organization (WHO, International Standards), BCR (European Union, CRMs) and the National Institute of Standards and Technology (NIST, USA, SRMs). Some important national producers of clinical reference materials are: the Chemicals and Inspection Testing Institute (CITI, Japan), National Institute for Biological Standards and Control (NIBSC, UIC), and Deutsche Gesellschaft fiir Klinische Chemie (DGIK). There are numerous commercial producers of secondary reference materials.

6.2.2 Elements

Elements are mostly classified to their abundance in the earth crust. The most abundant elements are known as bulk elements (H, C, N, 0, F, Na, Mg, Al, Si, P, S, C1, K, Ca), the others are considered as trace elements, with the exception of Fe. (Geld- macher-von Mallinckrodt and Meissner 1994).

In case of clinical chemistry/occupational toxicology subdivisions are followed according to function:

Essential electrolytes Essential trace elements Elements therapeutically used Non-essential elements

Because the physiological function of the elements vary widely, and for a number of elements different compounds with different effects physiologically exist, this group of compounds is described more comprehensively in the next sections. In a recent review the current problems with e.g. the determination of some trace metals are illustrated (Herber 1999).


6.2.2.1 Essential Electrolytes In case of essential elements, the most important issue is deficiency. Deficiency may be diagnosed by determining the element or compound containing the element. Sometimes it will be necessary therapeutically to administer the element in ion form. In this case higher concentrations than the normal levels can be expected.

Sodium, Na(1) has a normal concentration in human serum of 136-145 mmol/L (Tohda 1994) and makes up about 90 % of the cations present. (Many extracellular body fluids possess ranges from 7 mmol/L [mature milk] via 33 [saliva] to 145 mmol/ L [bile]). The reference method for determination is potentiometry with ion-selective electrodes (PISE).

Potassium is abundant in animal and plant cells (Birch and Pradgeham 1994). Hypoltalemia (deficiency) and hyperlalemia (accumulation of K[I]) may both occur. As the normal range of K[I] in plasma is small, and the consequences of hyperltalemia fatal, the method of determination must be precise and accurate to detect lower and higher than normal levels (hypokalemia and hyperltalemia, respectively). The preferred method of determination is PISE.

Calcium exists in the human body as Ca(I1) protein-bound and free Ca (11) ions (Dilana et al. 1994). For total extracellular Ca in plasma, serum and urine a definitive isotope dilution-mass spectrometry (ID-MS) method exist. Free Ca(I1) in plasmalserum can be determined with PISE, but no definitive and reference methods exist. For Ca in faeces, tissue and blood flame atomic absorption (FAAS) is used widely.

Magnesium deficiency has been long recognized, but hypermagnesia also occurs (Anderson and Talcott 1994). Magnesium can be determined in fluids by FAAS, inductively coupled plasma atomic emission spectrometry (ICP-AES) and ICP-MS. In tissue Mg can be determined directly by solid sampling atomic absorption spectrometry (SS-AAS) (Herber 1994a). Both Ca and Mg in plasma/serum are routinely determined by photometry in automated analyzers.

Chloride can be determined by photometry, by a coulometric titration method or PISE.

There are no special problems with the reconstitution or handling of these kinds of materials for electrolytes. The concentration of electrolytes is high, and no contamination problems are to be expected. Many commercial suppliers deliver reference materials for electrolytes in serum and urine.

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6.2.2.2 Essential Trace Elements Iron is, as part of several proteins, such as hemoglobin, essential for vertebrates. The element is not available as ion but mostly as the protein ligands transferrin (transport), lactoferrin (milk), and ferritin (storage), and cytochromes (electron transport) (Alexander 1994). Toxicity due to excessive iron absorption caused by genetic abnormalities exists. For the determination of serum Fe a spectrophotometric reference procedure exists. Urine Fe can be determined by graphite furnace (GF)-AAS, and tissue iron by GF-AAS and SS-AAS (Alexander 1994; Herber 1994a). Total Iron Binding Capacity is determined by fully saturated transferrin with Fe(III), but is nowadays mostly replaced by immunochemical determination of transferrin and ferritin.


Copper appears as the a2-globulin ceruloplasmin in the human body (Sarkar 1994). Deficiency of this protein in serum is characteristic of both Menkes’ and Wil- son’s diseases. Wilson’s disease is an abnormal storage of Cu(I1) in body tissues. Cu(I1) in biological material can be determined by spectrophotometry or by FAAS, ceruloplasmin in seium by a spectrophotometric method.

Selenium is required, but levels must fall into a narrow window. Both deficiency and toxicity symptoms occur. The element is also used therapeutically in cancer treatment. It is the co-factor of the enzyme glutathione peroxidase which is thought to play an important role in oxygen toxicity. The determination of Se in blood or serum is not easy, as many incorrect, inaccurate and imprecise methods have been published (Magee and James 1994). A suggested procedure for Se in body fluids is based on GF-AAS (Thomassen et al. 1994). For tissues SS-AAS may be used (Her- ber 1994a). Recent developments by Turner et al. (1999) show that LC-ICP-MS is sensitive and reproducible at low levels.

Cobalt is present in animals in vitamin B12 (cyanocobalamine) and thus is essential for humans (Thunus and Lejeune 1994). The determination of Co has little significance for the diagnosis of deficiency of cyanocobalamine. Instead, cyanocobalamine itself must be determined in serum. The determination of methyl malonic acid in urine seems more reliable (McCann et al. 1996).

Chromium deficiency may be related to the glucose tolerance factor (Herold and Fitzgerald 1994). The determination of this deficiency, however, is questioned, because the lack of accuracy of the Cr determination in the earlier publications.

Deficiency of manganese may lead to vitamin K deficiency (Chiswell and Johnson 1994) and to problems in prenatal and neonatal development of the brain.

Deficiency of molybdenum cofactor can lead to sulphite oxidase deficiency (Anke and Glei 1994).

Although vanadium seems to be an essential element, no deficiencies have been reported (Blotcky et al. 1994).

Tin is essential for animals, but the essentiality for humans is not clear (Anger and Curtes 1994).

Iodine is incorporated in thyroid proteins to form thyroxin and 3-I-thyroxine, both hormones essential for life. They are determined by immunochemical methods. Deficiency of I may lead to crop disease.

Fluorine as the anion F(1) is found in bone and tooth. Enhanced levels are toxic. F(1) can be determined by PISE.

There are a number of CRMs available for this group of elements in serum and urine (see Table 6.3). The most severe problems with the determination of these trace elements are contamination and loss. Therefore, strict protocols are necessary to prevent these problems. Contamination can be prevented by cleaning thoroughly all used utensils, and the use of highly purified chemicals. Loss is mostly due to exchange between the container walls and can be prevented by working at a pH<2.

6.2.2.3 Elements Therapeutically Used Lithium is therapeutically used in the prevention of major changes in mood which are characteristic of the affective disorders (Birch et al. 1994). The therapy can be


monitored by the determination of Li in serum, usually by F-AAS or flame emission photometry. As normal concentrations of Li in serum are very low, monitoring of the therapeutic high dose ( Li2C03, 30 mmol/day) is easy to perform. Concentra- tions of Li in serum must be in the range of 0.4-0.8 mmol/L. Higher levels of Li in serum may be toxic.

Gold is used therapeutically in chronic inflammations as rheumatic arthritis (Ishida and Orimo 1994). The dose is given in the form ofa gold complex, such as gold sodium thiomalate and Auranofin; toxic effects due to overdoses may appear. The most common method to monitor the therapeutic dose in serum or urine is GF-AAS.

Platinum is used therapeutically as cis-platin, carboplatin and iproplatin against tumors (Konig and Schuster 1994). Determination of Pt in serum must be carried out after enrichment procedures followed by GF-AAS.

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6.2.2.4 Non-Essential Elements These elements are sometimes called “toxic” elements. Although many elements belong to this group, a few only are encountered in the clinical or occupational laboratory. This is also reflected in the literature. For this reason only the most common elements are mentioned.

Lead has been known to be toxic since the Roman Empire. There are a number of acute effects known, e.g. anorexia, dyspepsia, constipation, colics, and toxic encepha- lopathy (Christensen and Kristiansen 1994). Most common effects to chronic exposure to lead are inhibition of heme synthesis, leading in severe cases to anemia, effects on the peripheral nervous system, and effects on the renal tubules. Exposure to Pb can take place both in the occupational and the general environment. Since the early 1980’s there have been many programs designed to reduce lead from the environment, including the removal of lead from gasoline, the banning of lead as a paint pigment, and replacement of lead water pipes.

The most common method used to monitor inorganic Pb is the determination of Pb in whole blood by GF-AAS. Exposure to organic lead (i.e. tetraethyl lead) can be monitored by the determination of Pb in urine by GF-AAS (Christensen and 10-is- tiansen 1994). Early effects of exposure to Pb on the heme synthesis can be monitored by determination of the inhibition of the enzyme 6-aminolevulinic acid dehydra- tase in whole blood or 6-aminolevulinic acid in urine by spectrophotometry.

Acute exposure to cadmium may lead to chemical pneumonitis and edema, but is rare nowadays (Herber 19g4b). Chronic exposure to Cd affects mostly the renal tubules and the lung. Exposure to Cd can take place both in the occupational and environmental area.

Since the 1980’s occupational and environmental exposure to Cd has been reduced due to banning of Cd in pigments, plastic softeners, fertilizers, and batter- ies. In some European countries (e.g. Sweden) Cd has been banned completely.

Monitoring of Cd exposure can take place by the determination of Cd in whole blood (reflects recent exposure) or urine (reflects body burden) by GF-AAS. Early effects can be monitored by the determination of a tubular protein (e.g. &microglobulin, retinol binding protein, a2-microglobulin) or the activity of an enzyme (e.g. N-acetyl @-D-glucosaminidase) in urine.

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Mercury exists as inorganic Hg (I) and Hg(I1) and as organic mercury. The toxic effects depend crucially on the binding form. In the past a number of local effects were reported when using sublimate (HgC12), e.g. effects on the oral cavity and the gastrointestinal tract. Exposure to high concentrations of mercury vapor may lead to a number of acute effects to the lungs. The central nervous system is the critical organ for the long-term exposure to mercury vapor or organomercury vapor compounds (Drasch 1994). Other effects are reported on the kidney (inorganic mercury) and on skin and mucous membranes (thiomersal). Incidence of amalgam contact allergy is rare. Biomonitoring of inorganic mercury can be performed by cold vapor atomic absorption spectrometry (CV-AAS) of mercury in urine. Organic mercury can be monitored by determination of mercury in blood by CV-AAS.

Aluminium is the most abundant element of the lithosphere. Although a large number of persons are exposed world-wide to Al, the incidence of pulmonary effects is low (Schaller et al. 1994). In the 1970’s the effect of A1 appearing in dialysis solutions on the central nervous system has become well known. increased Al could also be detected in several brain regions of patients with Alzheimer’s disease. For the determination in biological materials the most widely used method is GF-AAS.

From arsenic a number of different compounds exist, however, by far the most toxic forms are the inorganic As compounds (Stoeppler and Vahter 1994). In human environment exposure to As(V) is generally found. Acute exposure may lead to gastrointestinal effects, muscular cramps, and cardiac abnormalities but are rare nowadays. Long-term exposure through inhalation or ingestion may lead to a number of adverse health effects, including lung cancer, effects on the liver, the cardiovascular system, the heme system, and the nervous system. Exposure to inorganic As can be monitored by the determination of As in urine, but as all As species are excreted in urine, the determination of total As in urine gives an overestimation of the exposure. Instead a hydride AAS technique can be used to monitor the sum of

Tab. 6.3 and nonessential elements (3)

RMs for essential electrolytes ( I ) , essential and therapeutically used trace elements (2)

Category Producer Type of RM

1 NIST

BCR

Na, K, Ca, Mg and CI in serum, K, Ca, Mg and CI in serum, Ca in urine, C1 in serum Ca and Mg in serum

2

3

NIST

BCR

WHO

Cu and Se in urine, Fe in serum, F in urine, Li in serum, Au and Pt in urine Cu as ceruloplasmin and Fe as transferrine in serum, Li in serum Fe as ferritin in serum, Co as vitamin BIZ in serum

NIST

BCR

Pb in blood, As, Be, Cd, Cr, Cu, Mn. Ni and V in urine, Hg in urine Pb and Cd in lyophilized bovine blood


As(III), As(V), monomethyl arsonic acid, and dimethylarsenic acid, which gives a quick and reliable estimation of exposure to inorganic arsenic.

There are a number of other elements appearing from time to time in the laboratory. From these, chromium and nickel are most common. Both appear in enhanced concentrations in workers exposed to welding fumes, in galvanization processes, and in processing of ores. Prolonged exposure to Cr and/or N i causes cancer and affects the kidney. Preferred methods of determination of Ni and Cr in urine are GF-AAS. Because of the risk of contamination of the very low concentrations in urine, extreme precautions in sample handling and analysis must be carried out.

Table 6.3 lists reference materials for the elements mentioned in Sections 6.2.2.1-6.2.2.4.

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6.2.3 Organic Compounds

More than 70000 chemicals are recorded in the European Inventory of Known Chemical Substances and can be used in industry. As the majority are organic compounds, the importance of these compounds will be clear. Moreover, many of these organic compounds are solvents and volatile and may thus expose humans through the lungs or the skin, or are persistent and lipophilic and remain within the human body for many years as deposits in the fatty tissues.

6.2.3.1 Solvents Many organic solvents, including hydrocarbons, chlorinated hydrocarbons, alco- hols, esters, and ketones have the potential upon acute high level vapor exposure to cause narcosis and death (Andrews and Snyder 1996). Effects may be disorien- tation, euphoria, giddiness, confusion, paralysis, unconsciousness, convulsions and ultimately death. Distinct from the central nervous system (CNS) depression actions of solvents are specific toxicities associated with them (Andrews and Sny- der 1996). Examples of specific toxicities are: hemopoietic toxicity of benzene, (CNS) depressant effects of alkylbenzenes, hepatoxicity of certain chlorinated hydrocarbons, ocular toxicity of methanol, hepatoxicity and CNS depressant effects of ethanol, neurotoxicity of n-hexane and certain ketones, reproductive toxicity of ethylene glycol ethers, and carcinogenicity of dioxane. Because of the usage of solvents in many industries (i.e. paint, metal cleaning, glues, organic synthesis) and their volatile character, there is considerable exposure of workers to these solutions. In the general environment there may be sometimes exposure due to soil pollution.

Solvents or their metabolites are commonly determined by GC (Toltunaga et al. 1974) or GC-MS. In spite of the high importance of exposure to solvents, and the great number of determinations performed worldwide, reference materials for solvents in serum or urine are virtually nonexistent. There are a number of reference materials used in occupational hygiene, for example the ethanol in water standard from NIST (SRM 1828a) is commonly used in the clinical laboratory.

G.2 Clinical Application Fields I 207

6.2.3.2 Polyaromatic Hydrocarbons (PAH) PAHs, more correctly known as polyaromatic compounds (PACs) are common in the human environment, e.g. the exhaust of diesel engines, bitumen and asphalt production. Some of the PAHs are genotoxic and carcinogenic (e.g benz(a)pyrene). Even though PAHs are commonly determined by GC or HPLC, there are no matrix reference materials for PAHs in urine or serum. A number of reference materials certified for PAHs in animal tissue are available, but they are intended for environmental applications, see Section 3.4.

6.2.3.3 Pesticides Pesticides are used to control pests in agriculture and animal breeding. It has been known since the 1950’s that pesticide contamination occurs worldwide (e.g. DDT). Many pesticides are neurotoxicants poisoning the nervous system. A number of pesticides are acetyl cholinesterase inhibitors (Serat and Mengle 1973). Generally, pesticides determination has been performed by GC since the IgGo’s (Morrison and Durham 1971; Fournier et al. 1978). There are no reference materials for pesticides in urine or serum, although as with PAHs there are a number biological matrices certified for the content of various pesticides available for environmental food and agriculture analysis and which may have some application in clinical chemistry.

6.2.3.4 Persistent Compounds Polychloro-benzenes, polybromo-benzenes, and dioxins (TCDD) are among these compounds. They were discovered when the analysis techniques improved. Espe- cially the development of GC-MS has contributed to the knowledge of the distribution of these compounds. Effects on humans are the development of chloracne, sup- pression of the immune system, and some compounds are probably carcinogens (Shaw 1993). As a consequence of the ubiquitous nature of PCBs, humans are exposed via many sources.

Other than NIST SRM 1589, PCBs in human serum, there are no reference materials for these compounds in urine or serum. A number of reference materials are available for environmental samples, food and agriculture.

6.2.4 Proteins and Enzymes

Proteins are essential to all living systems. Proteins are macromolecules and, like all biological macromolecules, polymers (Alberts et al. 1994). The structural units of proteins (monomers) are about 20 amino acids. Although no clear line exists, proteins are generally considered to have minimal chain lengths of about 50 amino acids, corresponding to molecular masses near 5000 daltons. The most complicated proteins contain several thousand amino acids and have molecular masses of several million daltons. The functional diversity ranges from:

Enzymes, which have catalytic properties Antibodies, which serve as a weapon in the defense arsenal of the organism

208 6 General Application Fields I Structural elements, e.g. to define and maintain the architectural construc- tion Transport devices, e.g. for ions, oxygen, and lipids Metabolic regulators, including hormones. Animal proteins are classified as follows: Albumins, characterized by their solubility in water, and in diluted aqueous salt solutions Globulins, soluble in diluted aqueous salt solutions, but insoluble or slightly soluble in distilled water Protamines, among the smallest proteins with a molecular mass of 5000 daltons. They have a high basicity and are found in sperm Histones, which also have a high basicity and are found in combination with nudeic acid Scleroproteins, insoluble in most solvents. Localized in connective tissue, bone, hair, and skin. The two principal classes are the collagens and keratins Nucleoproteins, nucleic acid Lipoproteins. The lipid moiety of the lipoproteins is quite variable, both qua- litatively and quantitatively Mucoproteins are carbohydrate in nature Chromoproteins are pigments

There are many proteins in the human body. A few hundreds of these compounds can be identified in urine. The qualitative determination of one or a series of proteins is performed by one of the electrophoresis techniques. Capillary electrophoresis can be automated and thus more quantified (Oda et al. 1997). Newer techniques also enable quantitative determination of proteins by gel electrophoresis (Wiedeman and Umbreit 1999). For quantitative determinations, the former method of decomposition into the constituent amino acids was followed by an automated spectrophotometric measurement of the ninhydrin-amino acid complex. Currently, a number of methods are available , including spectrophotometry (Doumas and Peters 1997) and, most frequently, ELISAs. Small proteins can be detected by techniques such as electrophoresis, isoelectric focusing, and chromatography (Waller et al. 1989). These methods have the advantage of low detection limits. Sometimes, these methods have a lack of specificity (cross-over reactions) and HPLC techniques are increasingly used to assess different proteins. The state-of-the-art of protein determination was mentioned by Walker (1996).

Enzymes are mostly determined by some spectrophotometric methods in clinical chemistry laboratories, but immunochemical and molecular biological techniques are finding their way into routine laboratory procedures.

Protein macromolecules present in biological fluids are almost invariably hetero- geneous in their characteristics. They may be products of more than one gene in the population (allotypes in the case of proteins; isoenzymes in the case of enzymes), or a single individual (isotypes of proteins, allelozymes of enzymes), or be subject to post-translational modification. The result of this inherent molecular heterogeneity is that different forms of the same protein may behave differently with respect to


binding to anti-sera, while certain enzyme isoforms may also display different catalytic properties. The heterogeneity spectrum of reference and control materials may differ from that of biological fluids, and this can lead to differing behavior in the determination. This again, may lead to the problem of method-dependent results (Moss and Whicher 1995). The solution may be a rigorous standardization. This has been done for enzyme determination, but other than BCR CRM 470 hardly at all for protein determination.

6.2.5 Lipids

Lipids in living systems are by solvents extractable compounds. Among the lipids are the fatty acids, glycerides, steroids, terpenes, and complex lipids as lipoproteins. Fatty acids can be compared with detergents and have the capacity, i.e. in the form of micelles to solubilize organic material.

Fatty acids play an important role as a risk factor for cardiovascular diseases, that is by forming plaques within the arteria. Low density lipoproteins (LDL) are seen as the most important risk factor. In the clinical chemistry laboratory, both LDLs and HDLs (high density lipids, considered as an anti-atherogenic factor) are determined. Most used methods are spectrophotometry and immunochemistry, in dedicated laboratories ultracentrifugation. A handbook on this material has been written by Rifai et al. (1997). Certified reference materials for the determination of lipids in serum are provided by NIST.

6.2.6 Other Compounds

There are numerous other compounds which can be determined in human body fluids. For some classes of compounds, e.g. nitrogen compounds, hormones, and sugars, a few reference materials are available.

Nitrogen compounds commonly determined are creatinine, urea, and uric acid. Creatinine is an end product of the energy process occurring within the muscles, and is thus related to muscle mass. Creatinine in urine is commonly used as an indicator and correction factor of dilution in urine. Creatinine in serum is an indicator of the filtration capacity of the kidney. Urea is the end product of the nitrogen urea cycle, starting with carbon dioxide and ammonia, and is the bulk compound of urine. The production of uric acid is associated with the disease gout. In some cases, it appears that the excess of uric acid is a consequence of impaired renal excretion of this substance.

Hormones are regulatory substances from small molecules (e.g. nucleotides and steroids) to large polypeptides (e.g. insulin).

Carbohydrates (sugars) catabolism provides the major share of the energy require- ment for maintenance of life and performance of work.

Table 6.4 lists examples of reference materials mentioned in Sections 6.2.4- 6.2.6.


Tab. 6.4 a n d purified materials (4)

RMs for proteins in serum ( I ) , enzymes in serum (2) , lipids a n d other in serum (3), pure I

Category Producer Type of RM

1

2

3

4

WHO

BCR

NIST BCR

WHO

NIST

BCR

WHO NIST

WHO

Alphafoetoprotein, Ancrod, Anti-D Immunoglobulin, Anti- thrombin 111 total, Apolipoprotein B, Haemoglobin A2 and F Lysate, Heparin, Protamine; Protein C, Fibrinogen, Plasmin; a-Thrombin, Antithrombins, 6-Thrornboglobulin, Haemiglo- bincyanide cxl-acid Glycoprotein, Albumin. Alphafoetoprotein, a,-anti-Chy- motrypsin, a,-anti-Trypsin, a2-Macroglobulin, Apolipoproteine A1 and A2, Complements C3 and C4, C-reactive protein, Hae- miglobincyanide, Haptoglobulin, Immunoglobuline A,G,M, Prostate specific antigen (PSA), Transthyretrin, Thrombopla- stine, Thyroglobulin Albumin Alanine transferase, Alkaline phosphatase, a-Amylase, Creatine kinase, Creatine kinase; y-Glutamyltransferase, Lactate Dehy drogenase isoenzyme 1, Prostatic Acid Phosphatase Plasminogen Activator Inhibitor-1, Prekallikrein Activator, Streptokinase, Streptokinase and Streptodornase, Tissue Plasminogen Activator, Urokinase Cholesterol, Cholesterol HDL and LDL, Glycerides, Total glycerides, Glucose, Fat soluble vitamins Cortisol, Progesterone, 17 6-Estradiol, Creatinine, Creatinine interfering substances Chorionic gonadotropin, Follicle stimulating hormone Urea, Uric add, Bilirubin, Cortisol, o-Mannitol. o-Glucose, Sodium pyvate , 4-hydroxy-3-methoxy mandelic acid, 4-Nitro- phenol, 17 Amino adds in HCl, Angiotensin-I, Tripalmitin, Bone meal (8 elements), Bone ash (8 elements), Lithium carbonate Luteinizing hormone, Thyroid stimulating hormone

6.3 Food/Biological Milan lhnat and Wayne R Wolf

6.3.1 introduction

Generation of data on the nutrient content of agricultural products and foods forms the basis for estimating nutrient intakes of populations via dietary surveys, nutritional labelling for consumer protection, nutrition education for consumer food choice, home and institution menu planning and food purchase, and for research in nutrient requirements and metabolism. toxicant chemical composition is used to

assess effects of farm management practices, crop culture, and food processing on chemical content and implications for human health.

I *11 6.3 Food/Biological

Accurate food composition data can only be obtained by utilization of sound analytical methodologies and quality assurance systems. The use of well defined RMs is a vital part of this quality assurance. A summary of procedures for RM selection and utilization is presented here as a guide for monitoring and maintaining analytical data quality in the determination of inorganic and organic measurands in food and biological materials. The aggregate of all steps such as sampling, sample manipulation and measurement, subsequent to the point at which the RM is introduced into the scheme of analysis, will be monitored.

6.3.2 Food Matrix Triangle

Much of the analytical data on the nutrient content of foods is generated using official methods of analysis (e.g. AOAC International). An evaluation of AOAC Methods of Analysis for Nutritional Labelling is available (Sullivan and Carpenter 1993). While these methods have often been studied for a variety of food matrices, applicability over the entire range of food matrices has not been formally studied in most cases. In addition, RMs are not available over the entire range of food matrices (Wolf

In order to define this variety of food matrices, chemical composition differences that primarily influence chemical analytical measurements have to be considered. Major food components determining basic chemical make-up are the proximate composition of fat, protein, carbohydrate, ash, and moisture. Variations in ash content in general have a minor influence on analytical methods for other constituents and impact of moisture content can be controlled. Thus the major components influencing analytical performance are the relative levels offat, protein, and carbohydrate.

Southgate (1987) discusses the range of available RMs in terms of their fat, protein, and carbohydrate content. These constituents are presented graphically via a triangle wherein the relative position of each of these three proximate components is represented as IOO % at a separate apex and o % at the opposite side of an equilat- eral triangle as shown in Figure (5.1.

Drawing on this representation, an approach has been described to systematically describe selection of food products to evaluate the applicability of collaboratively studied methods over a range of food matrices (Wolf and Andrews 1995). A food matrix is described by its location in one of the nine sectors in the triangle. Foods falling within the same sector are chemically similar and thus should behave in a similar analytical manner. This same scheme can be used to select food matrices representing each sector for development of a series of RMs representing all foods.

In order to begin this selection process, the entire range offood matrices can be exam- ined. The proximate components of foods are plotted to determine into which of the nine sectors the foods fall. To develop an x/y plot of these sectors, values for x and yare assigned using the following equations based upon the% fat (a), % protein (b) and% carbohydrate (c) relative to the sum of these three components, normalizing these components to a dry weight, ash-free basis. Thus the s u m of a + b + cis IOO %.

1993).

212 G General Application Fields I Fat fOWo

Fig. 6.1 laborative study based on protein (Prot), fat and carbohydrate (Cho) content, excldding moisture and ash

Schematic layout o f food matrices suggested for a col.

y = a; x = (a + ab)/tan (60")

a = ( % fat x IOO)/ (% fat + % protein + % carbohydrate)

b= (% protein x IOO)/(% fat + % protein +% carbohydrate)

c = (% carbohydrate x IOO)/(% fat +% protein + % carbohydrate) = [IOO - (a + b)]

In some sectors, several materials may be necessary to account for differences in the type of protein, fat or carbohydrate. For example, some high-carbohydrate foods are high in sugar whereas others are high in starch or dietary fibre. As a preliminary approach, data contained in USDA databases on nutrient content of foods (USDA 1993) have been sorted and plotted using this food matrix organizational system (Wolf and Andrews 1995). These databases contain single ingredient items as well as multi-ingredient foods whose proximate content was determined by recipe. The normalized fat, protein and carbohydrate-by-difference data for 6675 foods are plotted in a scatter plot (Figure 6.2) on a dry weight basis. The data in each of the nine sectors were further analyzed to determine both the mean and the distance each food lies from the mean. Mean x and y values and the number of items for each sector are plotted in Figure 6.3, showing many more foods at the high end of the carbohydrate axis (Sector 5). The foods in each sector were then ranked by distance from the mean and cross checked with frequency-of-use data (USDA 1991).

I 213 6 3 Food/Biological

100

z

20

. -.. . ..\ . . . . . . * . . .

. :i. .: > . . ,. . ’.:. . . . . :- . . . ’......

0 20 40 60 80 100 Normalized Percent

Fig. 6.2 sumption Survey (USDA 1989-91)

Plot of6675 foods from the USDA Database for Food Con-

1 F

20 40 60

Fig. 6.3 Figure 6-2

Number offoods and mean point per sector from

The resulting tables (i.e. Table 6.5) list commonly consumed foods that are near the mean x and y for each sector. Commonly consumed foods are a real advantage when preparing RMs, because they tend to be readily available and inexpensive.

In Table 6.5 (sector 4), eggs, cheese, and chicken are commonly consumed foods and are possible candidates for RMs for foods falling into the proximate ranges for this sector (fat content 34-66 %, protein content 34-66 %, and carbohydrate content 0-33 %). Multi-ingredient items like soups, sandwiches and low-fat frozen dinners are the commonly consumed foods whose proximate contents are close to the mean for sector 7. These mixed dishes are possible candidates for RMs for foods with fat


Tab. 6.5 List of commonly consumed foods closest to the sector 4 mean (Wolf and Andrews 1995) I

Description Fat (57) Protein (55) Carbohydrate (57)

Egg, whole boiled 43.5 51.8 4.6 Cheese, swiss 46.3 47.9 5.7 Egg, whole poached 42.2 52.6 5.1 Egg, omelet/scrambled egg, no fat added 40.2 48.8 10.9 Chicken wing with skin, baked 43.7 51.5 4.8

content 0-33 %, protein content 34-66 %, and carbohydrate content 34-66 %. A list of key foods that supply 75 % of a given nutrient to the population has been developed (Haytowitz et al. 1996). It would be of interest to examine this list using this food matrix triangle approach to develop further recommendations for candidate RMs. The Standard Reference Materials Program of NIST has utilized this approach in setting priorities for development of several new food-based RMs. One outcome was the additional characterization of proximate contents for a number of RMs pre- sently available from NIST.

6.3.3 Available Reference Materials

Table 6.6 lists most of the available RMs, a listing of major producers and suppliers of all kinds of RMs is given in Chapter 8. Many materials have been characterized for elemental, isotopic and radionuclide content, but increasingly, materials are becoming available for a wide variety of organic measurands; see Section 2.1. An example of concentrations of nitrogen in biologicallfood RMs is given in Table 6.7. Tabulations as in Tables 6.6 and 6.7 (e.g. Ihnat 1988,1998b; International Atomic Energy Agency 1995; National Oceanic and Atmospheric Administration 1995) enable the analyst to locate materials of appropriate natural matrix composition and measurand concentration. In- dividual catalogues and reports (e.g. Bowman 1994; International Atomic Energy Agency 1998; Trahey 1998; Institute for Reference Materials and Measurements 1999) and appropriate websites should also be consulted.

6.3.4 Mode o f Application and Application Examples

A good presentation of general principles relating to RM and data quality concepts and use is given by Taylor (1993). Specific guidelines for the selection and utilization of RMs for monitoring and maintaining analpcal data quality in the measurement of inorganic measurands in plants and soils have been published (Ihnat 1993, 1998a, b). In order to properly use RMs, it is imperative that compliance with several preliminary requirements be established

(I) An appropriate analytical method must be applied to the task on hand by appropriately qualified and trained personnel.

6 3 Food/Bio/ogica/

Tab. 6.6 Examples of biological, food, agricultural and related RMs for chemical composition available from, principally, government agency suppliers (Ihnat 1988, 1992,1998a; International Atomic Energy Agency 1998; Institute for Reference Materials and Measurements 1999; National Oceanic and Atmospheric Administration 1995; Trahey 1998)4

RM group

Animal tissues

Foodstuffs

Plants

Biological waste materials

SupplieF:

BCR

NRCC

IAEA EPA NIST ARC BCR

IAEA LIVSVER NIES NIST

BCR

CANMET IAEA INCT NIES NIST BCR

Material

Bovine liver, pig kidney, mussel tissue (also for butyltin compounds), tuna fish (methylmernuy), tuna fish tissue (As speciation) Non-defatted lobster hepatopancreas, lobster hepatopancreas, dogfish liver, dogfish muscle Fish flesh Fish tissue Bovine liver, oyster tissue Animal muscle (pork), carrot powder, total diet, wheat flour Skim milk powder (elements), whole meal flour, bovine muscle, wholemeal flour, brown bread, cod liver oil (PCBs), rye flour, haricots verts (beans), pork muscle, mixed vegetables, carrot, bran breakfast cereal, unspiked milk powder (PCDDs, PCDFs), spiked milk powder (PCDDs, PCDFs), milk powder Rye flour, milk powder, whey powder Pork meat Tea leaves, rice flour, oyster tissue, wheat flour, rice flour Nonfat milk powder, spinach leaves, corn kernel, bovine muscle powder, whole egg powder, microcrystalline cellulose, wheat gluten, whole milk powder, durum wheat flour Aquatic phnts (Lugurosiphon major, Platihypnidium riparioides), olive leaves, beech leaves, hay powder, lichen, single cell protein, sea lettuce, rye grass, white glover, plankton Spruce twigs and needles Cotton cellulose, hay powder, grass Oriental tobacco leaves, Virginia tobacco leaves Pepperbush, chlorella, sargasso, Apple leaves, citrus leaves, pine needles, corn stalk Sewage sludge (PAHs), sewage sludge (domestic origin), sewage sludge (industrial origin), waste mineral oil (low level PCBs)

4 The majority of these RMs are available from the issuing organizations; several older materials may not be available from primary sources but may still be available in the secondary market (e.g. from existing stock in laboratories).

?<* For the suppliers EPA, ARC, LIVSVER, CANMET and INCT listed above that are not already mentioned in other chapters sources for further information are given in Chapter 8.

(2) Suitable quality control and quality assurance procedures should be in place and the analytical system must be in a state of statistical control.

(3) It must be ascertained that the method is measuring all of the measurand and the correct moiety.

216 6 General Application fields

Tab. 6.7 materials listed in increasing order of concentrationa)

Example of nitrogen concentrations in biological, food, agricultural and related reference I

Material

Microcrystalline Cellulose Corn Starch Corn Stalk Corn Bran Haricot beans Bush branches and leaves Pine Needles Rye flour Corn Kernel Rye bread flour Bush branches and leaves Pork meat Soft Winter Wheat Flour Spruce needles Olive Leaves Wheat bread flour Sea Lettuce Wheat flour Apple leaves Wheat flour Poplar leaves Beech leaves Hard Red Spring Wheat Flour Durum Wheat Flour Cabbage Citrus Leaves Peach leaves Tomato leaves Tea Aquatic Plant (I?. riparioides) Total diet Hay powder Aquatic Plant (L. major) Whole Milk Powder Kale Whole milk powder Tea Non fat milk powder Skim Milk Powder Spinach leaves Slum milk powder Whole Egg Powder Oyster tissue Bovine Liver Pork liver Single Cell Protein

Codeb)

NIST-RM-8416 NIST-RM-8432 NIST-RM-8412 NIST-RM-8433 BCR-CRM-383 GBW-07602 NIST-SRM-1575 BCR-CRM-381 NIST-RM-8413 CSRM-12-2-05 GBW-07603 LIVSVER-SMRI-941 NIST-RM-8438 BCR-CRM-101 BCR-CRM-062 CSRM-12-2-04 BCR-CRM-279 BCR-CRM-382 NIST-SRM-1515 GBW-08503 GBW-07604 BCR-CRM-100 NI ST-RM-8437 NIST-RM-8436 GBW-08504 NIST-SRM-1572 NIST-SRM-1547 NIST-SRM-1573a GBW-07605 BCR-CRM-061 NIST-SRM-1548 BCR-CRM-129 BCR-CRM-060 NIST-RM-8435 BOWEN’S KALE

GBW-08505 GBW-08509

NIST-SRM-1570a

BCR-CRM-380

BCR-CRM-063

BCR-CRM-O63R NIST-RM-8415 NIST-SRM-1566a NIST-SRM-1577a GBW-0855 1 BCR-CRM-273

Concentrationc)

200 670

6970 8840

10500 12000 12000 12500 13750 14000 15000 16800 17560 18890 19500 20000 20800 21200 22500 23900 25600 26290 26900 27070 28000 28600 29400 30300 33200 33500 34400 37200 41200 41820 42790 45000 48800 55100 58800 59000 62300 63000 68100

107000 108600 121000

I 217 6.3 Food/Bio/ogica/

Tab. 6.7 Continued

Material Code b,

Pork muscle Bovine Muscle Powder Prawn Wheat Gluten Human hair

BCR-CRM-384 NIST-RM-8414 GBW-08572 NIST-RM-8418 GBW-07601

Concentrationc)

137000 137500 143000 146800 149000

a) Information has been adapted from International Atomic Energy Agency (1995) and Ihnat (1988) as well as personal information and includes certified and informational concentration values.

b) Code is a combination of supplier code and identity assigned to the product.

c) Concentrations are reported as mg/kg on a dry basis.

This table is for information and discussion only; original certificates or information sheets provided with the Reference Materials must be consulted for actual concentrations and uncertainties.

6.3.4.1 The RM and the commodity undergoing analysis must be very similar with respect to matrix and measurand concentration and form (e.g. native form, speciation). By consulting information as in Table 6.6, giving a descriptive name of the product, select the RM(s) approximating the laboratory sample to be controlled with respect to matrix (i.e. by RM name). By consulting a measurand concentration table, as exemplified in Table 6.7 for nitrogen, independently select RMs based on concor- dance of the measurand concentration in the RM and the level anticipated in the sample. Use these two selection criteria to arrive at appropriate RMs. Several RMs, spanning the concentration range of interest is preferred, but this is not always possible due to inadequacy of the world RM repertoire.

Procedures for Reference Material Selection and Use

6.3.4.2

Following RM certificate instructions for material usage and handling, incorporate the RM into the scheme of analysis at the earliest stage possible, i.e. prior to the beginning of sample decomposition. Take it through the entire analytical procedure at the same time and under the identical conditions as the actual analytical samples in order to correctly monitor all the sample manipulation and measurement steps.

Procedures for Reference Material Utilization

6.3.4.3

Results from the analysis of the RM and the certified value and their uncertainties are compared using simple statistical tests (Ihnat 1993,1998a). If the measured concentration value agrees with the certified value, the analyst can deduce with some confidence that the method is applicable to the analysis of materials of similar composition. Ifthere is disagreement, the method as applied exhibits a bias; and underlying causes of error should be sought and corrected, or their effects minimized.

Performance Interpretation and Corrective Action

218 G General Appiication Fie/ds

6.3.4.4 Incorporation of RMs into schemes of analysis is still evolving. Official and recommended methods of analysis often still do not stipulate RMs as an integral part of the analytical method. An important major use of existing RMs is quality control of analysis and certification activities for the development ofnew RMs. In earlier years of RM development, and surprisingly even more recently, very little allusion is made to the use of existing RMs for quality control. Examples of recent usage are the certification activities by BCR (IRMM) (Quevauder et al. 1993; Pendlington et al. 1996; Lamberty and Kra- mer 1gg8), NIST (Donais et al. 1g97), IAEA (Horvat et al. 1997). and Agriculture and Agri-Food Canada (AAFC) (Ihnat 1990.1994). In some BCR work (Quevauviller et al. 1gg3), the report simply indicates that the performance of the method was verified by analyzing available RMs or other materials. In the BCR certification of several foods for dietary fibre (Pendlington et al. 1996), Rye Flour BCR-CRM-381 was used for quality control of one of the fibre methods, while in the certification of the trace elemental content of a replacement bovine liver, C R M - I ~ ~ R (Lamberty and Kramer 1gg8), the previous similar material, CRM-185, was used. In the NISTcharacterization ofthree mussel SRMs (1g74a, 2974 and 2976) for Hg and MeHg (Donais et al. 1gg7), previously analyzed SRM-2976 was used as a control for measurements on the other two materials. Additionally, Oyster Tissue SRM-1566a, Montana I Soil sRM-2710, and Lobster Hepato- pancreas NRCC-TORT-I were used as controls for all three tissues. The IAEA certification oftotal Hg and MeHg in mussel IAEA-142 (Horvat et al. 1gg7), involved Dogfish Muscle NRCC-DORM-I and DORM-2, Lobster Hepatopancreas NRCC-TORT-I and TORT-2, Non-defatted Lobster Hepatopancreas NRCC-LUTS-I, Marine Sediment NRCC-MES S-I, Tuna Fish Homogenate IAEA-350, Copepod Homogenate IAEA-MA-A- I, Oyster Tissue NIST-SRM-1566 and 1566a, Orchard Leaves NIST-SRM-1571, Albacore Tuna NIST-RM-50, and Human Hair BCR-CRM-397. The authors judged that only NIST-SRMs 1566 and 1566a fulfilled the matrix/concentration matching criteria exactly. RM development at Agriculture and Agri-Food Canada of 12 food RMs for NIST, incorporated existing RMs for quality control (Ihnat 1990,1994). Homogeneity assessment by solid sampling graphite furnace atomic absorption spectrometry of Pb and Cu in Bovine Muscle Powder 136 (initial assigned numbering), Wheat Gluten 184, Corn Bran 186, Durum Wheat Flour 187, and Whole Egg Powder 188 (Ihnat 1990) used Spiked Skim Milk Powder BCR-CRM-150, Wheat Flour N I S T - S R M - I ~ ~ ~ ~ , and Bovine Muscle BCR-CRM-184 for checking instrument performance and comparative behavior. In the subsequent full-scale inter-laboratory characterization campaign RMs included: Non Fat Milk Powder NIST-SRM-1549, Rice Flour NIST-SRM-1568, Orchard Leaves NIST-SRM-1571, Citrus Leaves NIST-SRM-1572, Tomato Leaves NIST-SRM-1573, Pine Needles NET-SRM-1575, Bovine Liver NIST-SRM-1577, Corn Stak NET-RM-8412, Corn Kernel NIST-RM-8413, Pepperbush NIES-CRM-I, Chlorella NIES-CRM-3, Tea Leaves NIES-CRM-7, Rice Flour NIES-CRM-10, Wheat Flour IAEA-V-Z/I, Animal Mus- cle IAEA-H-4, Rye Flour IAEA-V-8, Cotton Cellulose IAEA-V-9, and Bowen’s Kale.

Examples ofApplication o f R M s to Certification ofother R M s I

6.3.4.5 Several recent examples of the incorporation of food RMs in analytxal work are presented in Table 6.8. These applications do not necessarily adhere to the foregoing

Examples of Applying RMs in Analyses

Tab.

6.8

E

xam

ples

of

rece

nt a

ppli

cati

ons

offo

od R

Ms

for q

ualit

y co

ntro

l in

the

anal

ysis

of f

oods

and

foo

d pr

oduc

ts

Mat

rix,

mea

sura

nd

Met

ho&

<

Fe in

dup

lica

te d

iet s

ampl

es

A1 i

n te

a an

d c

offe

e C

d in

veg

etab

les

But

yric

aci

d in

edi

ble

fats

P,

S, K

Ca,

Ti,

Mn,

Fe,

Ni,

Cu,

Zn,

Se,

Rb,

Ba,

Pb

in te

a 55

maj

or a

nd tr

ace

elem

ents

in D

anis

h cr

ops

PCB

s in

cod

, mus

sel a

nd

sh

rim

p fr

om B

elgi

an c

onti

nent

al

shel

f I i

n D

anis

h da

iry

prod

ucts

A

s(II

1) a

nd A

s(V

) in

sea

food

ET

AA

S E

TA

AS

D-A

T-F

AA

S

GC

T

XR

F

GC

ICP-

MS

HG

AA

S

HR

-IC

P-M

S

K, M

g, C

a, M

n, Z

n, F

e, C

u, A

l, N

a, N

i, A

s, M

o, C

d IC

P-A

ES

FAA

S in

Vie

tnam

ese

rice

IC

P-M

S

Na,

Mg,

P, I

<, C

a, M

n, F

e, C

o, N

i Cu,

Zn

Se,

Mo

ICP-

AE

S in

soyb

ean

flou

r IC

P-M

S

As,

Cd,

Cr,

Cu,

Fe,

Mn,

Ni,

Pb, P

t, S

n, V

, Zn

IC

P-A

ES

in I

tali

an h

oney

Q

-IC

P-M

S H

R-I

CP-

MS

RM

use

d

NIS

T S

RM

156

7, W

heat

flou

r IA

EA

H-9

, Mix

ed h

um

an d

iet

GB

W 0

8571

, Mus

sel

BC

R C

RM

164

, Anh

ydro

us m

ilk

fat

GB

W 0

8505

, Tea

N

IST

SR

M 1

567a

, Whe

at fl

our

BC

R C

RM

349

, PC

Bs

in C

od li

ver o

il

BC

R C

RM

063

R, S

kim

milk

pow

der

NR

CC

DO

RM

-1 a

nd

DO

RM

-2, D

ogfi

sh m

uscl

e N

RC

C T

OR

T-2

, Lob

ster

hep

atop

ancr

eas,

B

CR

CR

M 2

78, M

usse

l N

IST

SR

M 1

56G

a, O

yste

r N

IES

CR

M 1

0, R

ice

flou

r

NIS

T S

RM

156

8a, R

ice

flou

r N

IST

SR

M 1

515,

App

le le

aves

B

CR

CR

M 2

81, R

ye g

rass

B

CR

CR

M 1

91. B

row

n br

ead

* M

etho

d ab

brev

iatio

ns: D

-AT-

FAA

S (d

eriv

ativ

e fla

me

AA

S with a

tom

tra

ppin

g), E

TAA

S (e

lect

roth

erm

al A

AS)

, G

C (

gas

chro

mat

ogra

- ph

y), H

GA

AS

(hyd

ride

gen

erat

ion

AA

S), H

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suggested mode of application principles, but exemplify current usage. Increasing interest in control of analytical data quality and awareness of the usefulness of RMs is leading to more routine use of RMs in daily analytical activities.

I

6.4 Applications o f Reference Materials in the Geological Sciences

Jean Kane

6.4.1 Introduction

The geological sciences are involved in studying the naturally occurring materials of the earth and solar system: (I) to understand the fundamental processes of crustal formation on earth and solar system evolution, and (2) to evaluate the crustal materials of potential economic value to man. Prior to the I ~ ~ o ’ s , analyses were carried out exclusively using classical analytical techniques, with detection limits on the order of 0.01-0.1 % (mass fraction). The number of elements contained in any sample could be as extensive as the periodic table, but very few of these could be determined. The development of instrumental techniques revolutionized the analysis of geochemical samples, beginning in the 1930’s.

Natural matrix reference materials of geological samples to support geochemical analyses were among the earliest to have been produced by NBS or NIST. For example, an argillaceous limestone was certified in 1906, while zinc, manganese, and iron ores date to 1910. All of the geological reference samples developed prior to G-I and W-I (Ahrens 1951) support the economic valuation of ores for commerce; none support basic geochemical studies of crustal processes. Regardless, classic work of both Clarke and Washington (1924) and Goldschmidt (1929) in deriving the average abundances of igneous rocks in the earth’s crust was completed without reference sample support; that work has stood the test of time extremely well. The same can be said for the work of Goldschmidt and Thomassen (1924) in developing data for rare earth geochemistry.

A significant change in geochemical analysis, and in the demands for natural matrix reference samples to support the analysis of geochemical materials, came with the advent of instrumental methods of analysis. The historical roots of these instrumental methods date from the mid-1880’s to the early goo's, but only later were the methods used in routine rock analysis. This use of instrumental methods of analysis generated a demand for rock reference samples, that could be used for calibration purposes. The earliest of them were analyzed by classical methods to determine major and minor oxides

The development of G-I and W-I (Ahrens 1951; Fairbairn et al.1951; Stevens et al. 1gG0) was the response to this demand with respect to dc arc emission spectrography. As similar samples are used routinely in calibration for XRF and INAA analyses, many geological samples have been developed as reference materials since that time to support geoanalysis (Potts et al.Iggz). Just as the change from classical to instrumental methods of analysis changed the nature of demands for reference

I **' 6.4 Applications of Reference Materials in the Geological Sciences

samples, so the new methods changed the nature of geochemical research (Potts et al. 1993). As it became possible to determine many elements simultaneously, and at lower detection limits than were achieved with classical methods, it became possible to study previously hidden geological processes. That in turn generated new demands on analytical capabilities, to probe even further into unknown geological processes. The synergistic process continually redefines what is needed in the way of reference samples to support method validation and to provide calibration materials. Table 6.9 summarizes the history of the issuance of geochemical reference samples that was inspired by, and resulted in, production of these materials.

Tab. 6.9 Timeline of key geological reference materials"

Year issued

1906 1919 1910 pre-1918 1910 1950s

1967 1964,1980 1968,1984 1982 1970 1970 1971 1975 1975 1975 1975 1976 1981 1981 1984 1990 1994 1982 1988 1992 1982 1987 1987

Reference sample description

Argillaceous limestone Zinc ore Manganese ore Sibley iron ore Norrie iron ore Granite Diabase Columbia River basalt Essey-la-Cote basalt Kitamatsuura basalt Tholeiitic basalt Sphalerite concentrate Nickel ore concentrate Molybdenum ore Platinum ore Jasperoid hot springs deposit Copper mill head soils Hawaiian basalt Rhyolite Basalt Icelandic basalt Devonian Ohio shale Zinnwaldite Estuarine sediment Buffalo River sediment Contaminated soils Trace elements in glass Mean oceanic water Belemite

Designation

NBS 1 NBS 2 NBS 25 NBS 27 NBS 28 USGS G-1 USGS W-1 USGS BCR-1 CRPG BR and BE-N JGS JB-1, JB-la

JGS 19 JGS 20

MINTEK SARM-7

JGS JB-2

CANMET PR-1

USGS GXR-1, -3 USGS GXR-4 USGS GXR-2, -5, -6 USGS BHVO-1 NIST SRM 278 NIST SRM 688 USGS BIR-1 USGS SDO-1 IWG ZW-C NIST SRM 1646 NIST SRM 2704 NIST SRMs 2710,2711 NIST SRMs 610-617 IAEA VSMOW IAEA VPDB

* Over 300 geological RMs have been developed over the years. Those listed above have been mentioned in the text, and may be considered representative of the full number available. A complete listing may be found in Potts et al. (1992) or in the July 1994 special issue of Geo- standards Newsletter


The types of natural matrix materials available for geochemistq the means of production, and the applications of these materials in analytical problem-solving are highly varied. It is the purpose of this Section to briefly review these materials and their uses, citing a number of specific applications. Because reference samples for environmental analyses form the subject of another book (Zschunke ~ O O O ) , this particular application in using geological reference materials will receive only brief mention here, despite a very close link between geological and environmental RMs in terms of both exploration and global mapping applications, as discussed below. With apologies to the reader, space limitations dictate that only a few key references of the hundreds that might support this review can be included. Each cited reference contains many others that present the broader perspective.

I

6.4.2 Producers of Geochemical Reference Materials

Historically, national geological surveys around the world, working in collaboration with university laboratories, and not national metrology laboratories, have been the major producers of reference materials supporting studies in baseline geochemistry. This is seen in the history of the development of G-I and W-I by the United States Geological Survey (USGS). The initial cooperative investigation of analyses involved the Department of Geology at Massachusetts Institute of Technology, the Office of Naval Research in Washington, DC, Carnegie Institute of Washington, and the Geo- chemistry and Petrology Branch of USGS (Fairbairn et al. 1951; Stevens et al. 1960). The aim was to provide calibration samples for the developing technique of dc arc atomic emission spectrography. In the end, these samples were recognized as the first geochemical reference samples supporting the analysis of typical crustal rocks, rather than ores and concentrates.

Since then, numerous other natural rod< reference materials were developed by USGS, by the Centre de Recherches Petrographique et Geochimiques and Association National de la Recherche and by others (Potts et al. 1993) to assure the closest possible matrix match between calibration and analytical samples. In 1981 two rocks were issued by NBS as certified reference materials (Uriano 1981). Today the Japanese Geological Survey and the Chinese Institute of Geophysical and Geochemical Exploration are per- haps foremost among producers in terms of numbers of reference samples supporting geological studies that have been produced in the past decade or two.

Reference samples supporting mineral exploration came both from metrology laboratories in countries having extensive mineral potential (e.g. Canada, South Africa) and from geological surveys (e.g. USGS, British Geological Survey). More recently, the geological materials that metrology laboratories like NIST have certified as reference materials have focused on elements important to studies of environmental pollution. It should be noted that many of these environmentally toxic metals are also ore “pathfinder” elements, of great importance in geochemical exploration for untapped mineral resources.

For research analysis, the demand is generally in front of the availability of reference materials. For routine production analysis, this is less often the case, but in

I 223 6.4 Appfications ofRe&rence Materids in the Geobgical Sciences

some instances is still a problem. For example, rare earth elements and high field strength elements are crucial in understanding the evolution of crustal rocks from the mantle. While close to 300 reference samples have been developed since 1951 (Potts et al. 1993). few reference materials are yet available with well established reference values for these important elements, or for the platinum group elements so important in exploration programs today (Kane 1991; Potts and Kane 1992). Further, over IOO research and routine laboratories are performing microanalysis on geologic samples using the electron probe, the ion probe, laser ablation-mass spectrometry, etc. to determine these elements, but not a single reference material has been certified either in bulk rock or at microsample masses for these applications (Pearce et al. 1997; Potts 1997).

6.4.3 General Application: Calibration of Instrumental Measurements

The use of reference samples for method calibration and development/validation occurred hand-in-hand with the development of all modern instrumental methods of analysis. In fact, the two developments are intimately linked with one another. As already noted, G-I and W-I (Fairbairn et al. 1951; Stevens 1960) illustrate first instance of reference samples specifically developed for calibration purposes. Fol- lowing that, the use of BCR-I as a reference sample throughout the lunar program (Science 1970) is a prime illustration of the quality assurance and method validation applications in large-scale inter-laboratory measurement programs.

The Fairbairn et al. (1951) report on the analysis of G-I and W-I presents a comparison of data obtained by 34 chemists using classical methods of analysis and participating in “the first step in what is probably the most comprehensive study ever taken in rock analysis.” The report goes on to state that “The disparity in results is too great at this preliminary stage to justify the assignment of “correct” values for the composition of the samples.” Thus began the first comprehensive attempt to certify natural matrix geological materials for many commonly determined elements in each such sample. The process “to locate and correct discrepancies” and thus produce an “improvement of analytical procedures and a more accurate esti- mate of the actual composition” follows the process currently recommended in I S 0 Guide 35 (1989) for certifications of reference materials. The process continues today throughout the geoanalyhcal community, with varying degrees of success.

It is important in this regard to recognize two things. First, IS0 Guide 32 (1993) recommends using at least ten reference samples to establish a calibration line which is the least squares fit of their signals and concentrations. Few method protocols specify the use of so many standards in defining the calibration line. Typically only one standard is used in instrumental neutron activation analysis; the software used with some commercial inductively coupled plasma spectrometric instruments is based on two-point calibration. However, the calibration error must be incorporated into the overall uncertainty of the measurement; and that calibration error will be relatively high unless uncertainties for reference material values are very small and/or many such samples are used in defining the calibration line. Second, there


are not enough reference samples characterized for some elements to meet the I S 0 Guide requirements for calibration with reference samples in many cases. And yet that i s a key application of these materials in geoanalysis.

Examples of using reference samples for calibration can be found in several chapters of the USGS Methods for Geochemical Analysis (Baedecker 1987). Solid reference sample powders are used in calibrating the dc arc emission, energy-dispersive X-ray and instrumental neutron activation analyses described, while acid-dissolved rock reference samples are used for ICP emission analyses and fused reference samples are used for wavelength-dispersive X-ray analyses.

I

6.4.4 General Application: Method Development and Validation

Identification of sources of analpcal bias in method development and method validation i s another very important application of reference materials in geochemical laboratories. USGS applied simplex optimization in establishing the best measurement conditions when the ICP-AES method was introduced as a substitute for AAS in the rapid rock procedure for major oxide determinations (Leary et al. 1982). The optimized measurement parameters were then validated by analyzing a number of USGS rock reference samples for which reference values had been established first by classical analyses. Similar optimization of an ICP-AES procedure for a number of trace elements was validatedby the analysis of USGS manganese nodule P-I (Montaser et al. 1984).

Another excellent example of the use for method development and validation appears in Morrison and Richardson (1996). Their laboratory was analyzing many samples of Li ore and related samples for Ba, among other elements, using a routine XRF procedure. The reference sample chosen as a control sample for the run was the zinnwaldite ZWC (Govindaraju et al. 1gg4), for which analyses produced a value approximately twice the reference value. Investigation ofthat result identified a Rb overlap in the X-ray spectrum that had not previously been observed in use of the method.

Similarly, some INAA data contributed to the derivation of a reference value for Ba in SDO-I were biased high by an interference from Io3Ru (Wandless 1993). The lo3Ru is a fission product of U, whose concentration of 40 pg/g i s relatively high in SDO-1. In this case, no appropriate reference sample was available for analysis to control the SDO-1 results; the interference was identified through the disagreement between INAA data and data produced using XRF and ICP-AES methods on the same sample. A bias-free method again resulted when analysis of an atypical type led to detection of a rarely encountered but sizeable spectral overlap. Once identified, correction was straightforward.

6.4.5 General Application: Quality Control in Multilaboratory, or Long-Term Within Laboratory, Studies

Frequently, many laboratories around the world are joint participants in major geochemical studies. One example already mentioned i s the lunar program of almost

I 225 G.4 Applications of Reference Materials in the Geological Sciences

thirty years ago (Science 1970). In such studies, it is important that all laboratories involved analyze a common sample. This allows true variability between samples for the program to be distinguished from analytical variability due to method discrepancies between laboratories.

BCR-I, a Columbia River basalt developed by USGS, was the prime sample used for this purpose in the lunar program. While many participating laboratories reported data for BCR-I, there was little overlap between laboratories in the elements determined. As a result the use of the sample contributed more to extending the characterization of BCR-I than to providing control oflunar program analytical data (Flanagan 1976). BCR- I and other basalts, (e.g. BHVO-I, BIR-I, BR, BE-N, JBI, JBIa, JB2, and JB-3) continue to be used for this purpose: they are particularly appropriate control samples in studies of large igneous provinces, including continental flood basalts. These studies will be discussed for the specific application of petrogenic modelling below.

In global mapping programs, extensive analytical data from many laboratories, that may or may not be in harmony, is used (Xie 1995). These mapping programs are direct outgrowths of geochemical exploration programs. They aim to uni@, in a single international database, all exploration data developed throughout the world, in order to obtain a consistent global overview of mineral occurrences. In this regard, reference samples provide a means of normalizing all data to a common basis, to provide a coherent world-wide map. Once the procedure is established, the mapping could cover environmental pollution as well as mineral source identification. The difficulty in such data normalization is that the same reference sample is not necessarily used in, or even available to, all laboratories throughout the long life of the mapping program.

Similarly, within laboratory, use of a common reference sample throughout the life of an analytical program spanning months or years, assures coherent data over the life of the program. General quality assurance and control using reference materials, as carried out at the Ontario Geological Survey, is described by Richardson et al. (1996), Likewise, the use of an in-house reference basalt BB-I is described in Taggart et al. (1993). Specific applications of this use of reference materials supporting a variety of geochemical studies are discussed below.

6.4.6 Specific Application: Geochemical Exploration

Applications of geological reference samples to mineral prospecting and economic evaluation of ore potential is the only application with a history dating back before the issuance of G-I and W-I in 1951. It is an area in which data quality or lack thereof has serious economic impacts, hence the very early development of certified reference materials mentioned previously. An extensive study of the state of ore analysis was undertaken by the Institute of Geological Sciences (now the British Geolo- gical Survey). Nineteen ores and concentrates, of varied matrix, were distributed to 38 laboratories; more than 1532 results were received (Lister and Galagher 1970).

The data showed many analytical discrepancies that highlighted the need for ore reference samples of different matrices than those already available and/or certified


for additional elements. An outgrowth of that survey was another conducted almost immediately by IGS for the purpose of developing reference ores (Lister 1g77), and concurrently, the development of reference ores by both South Africa (Steele et al. 1975) and Canada (Faye 1971).

Mineral exploration, the search for economic ore deposits, requires somewhat different reference samples than those used in ore valuation. Soil or sediment and water samples are frequently used in the search when mineralized areas of abundant outcrop or those covered only by thin locally derived overburden are being eval- uated. In such cases, it is virtually impossible not to detect the mineralization from an analysis of ore elements in these types of samples. Later, as the mineral deposits closest to the surface were exploited and then played out, new deposits occurred at progressively greater depths, and these sample types were less and less effective as markers in the search (Hoffman 1989).

New exploration techniques, and new reference materials in support of them, were needed. One major change was in the use of ore pathfinder elements, rather than the ore elements themselves, for exploration purposes. For example, instead of analyzing samples for the primary Au ore element, samples were analyzed for As, Hg, and W pathfinders that pointed to “hidden” gold deposits. The pathfinder elements occur in association with ore veins, but have a much broader spread than the mineralized area itself. However, measurement of the pathfinder elements requires methods with better detection limits than were needed in earlier exploration programs, as the pathfinders typically are not as enriched as the ore elements, in comparison to baseline crustal levels.

Another major change was the shift from extensive use of field laboratory exploration techniques to the laboratory techniques like ICP-AES and INAA. These produce a higher quality data than had resulted from the dc arc and other field techniques, with respect to both repeatability of measurement and improved detection limits. The metrology laboratory certifications for As and Hg in soils and sediments as key environmental toxins provided strong support to mineral exploration programs.

The GXR samples illustrate both sound use and serious misuse of reference samples developed specifically for mineral exploration. The series was developed in an expanded USGS program to identify exploration targets as likely sources of strategic minerals, and thus intended primarily for calibration and/or control of dc arc emission “six-step” field analyses (Alcott and Laltin 1975). These field analyses provided data with a ‘33 % relative standard deviation. Reference values with such wide uncertainty intervals were adequate in establishing a yes/no conclusion regarding the presence of an ore element at an economically recoverable concentration, so long as the concentration was well below or well above the cutoff value. The GXR samples were also analyzed extensively by AAS following an aqua regia leach procedure that efficiently attacked sulfide minerals, but not silicates, thereby highlighting primary mineralization patterns (Ward et al. 1969). These data contributed extensively to establishing the reference values for the ore elements. Used in control of similar analyses, these samples played a very important role in supporting exploration programs.

However, laboratories later began to use the GXR samples for very different purposes. Control of INAA and XRF determinations of the ore elements was sometimes

I

I 227 6.4 Applications of Reference Materials in the Geological Sciences

attempted, but was inappropriate as these techniques measure total, not sulfide-specific, concentrations of the ore elements. Additionally, uncertainties of the reference values exceeded those of the XRF and INAA measurements in-laboratory, further confounding the use of the materials for calibration and/or control. Serious problems resulted from this misapplication of the GXR reference samples in analytical laboratories. A further misapplication occurred when the materials were used for controlling the analysis of additional elements that could be measured by XRF, in particular for the major oxides. Homogeneity of the materials had been established as adequate for analysis of the ore elements. However, that conclusion could not be extended to all elements that later were measured in the samples (Kane et al. 1992).

Also consider the use of NIST sediments 1646, 2704, and soils 2709-2711 in exploration geochemistry. These samples were certified largely in view of the demand for samples to support monitoring of toxic elements in environmental samples. However, many of the elements certified overlap either the list of primary ore elements or the list of “pathfinder” elements. Thus, these samples may legitimately be used in a very different application than the one that prompted certification. The sample matrix is ideal for the alternative application, and so is the suite of certified elements.

Assume that without the proper use of reference samples in an exploration program, a site is purchased that is in fact barren. Hill (1974). for example, cites a 20 % added analytical cost for quality control and quality assurance. He further cites a possible cost of $220 million for purchasing and developing a mine site. The analytical expense for QA\QC based on use of reference samples is trivial in comparison to the potential loss, if the analyses of exploration survey samples are faulty and the mine worthless as a result.

6.4.7 Specific Application: Petrogenic Modelling Based on Bulk Rock Analysis

Among the quality control uses of reference samples, petrogenic studies to understand the genesis of large igneous provinces and zones of mineralization during earths long history were cited. This application is one which illustrates the synergy of developing analytical methodology and geochemical models for earth processes particularly well. Clarke and Washington (1924) published the first attempt at cal- culating average crustal abundances of major and minor oxides in crustal rocks. Shortly thereafter, Goldschmidt (1929) published results of a similar calculation, based on the analysis of different suites of rock. In both cases, the data used was obtained entirely using classical methods of analysis, and was limited to the 12 most abundant oxides that form the rock matrix. At about the same time, Goldschmidt and Thomassen (1924) used X-ray diffraction to make the first extensive geochemical study of the rare earth elements.

Modern geochemical studies use data for a much larger suite of elements, determined at much lower concentrations, to model the tectonic movements of continental plates, and to understand the sources of magma generated in that process (e.g. Lightfoot 1993; Sutcliffe 1993). The key elemental suites include the “incompatible”


rare earth elements and the high field strength elements. Enrichment and depletion patterns of these elements in igneous rocks as compared to average crustal abundances "fingerprint" the source areas for different volcanic events. Major oxide patterns are also informative in distinguishing magma types.

The USGS basalts BCR-I, BHVO-I and BIR-I are among the most frequently used reference samples for analyses performed by XRF, INAA, and ICP-MS. The reference values available in many cases do not meet the Uriano and Gravatt (1977) criterion of being known with three to ten times greater certainty than the data produced in routine analysis. Until metrology laboratories develop a certified reference basalt, with values for these critically important elements, the situation is unlikely to change. Reference values developed through inter-laboratory programs, and based on the agreement in results between two or more different methods of analysis, have not produced values with uncertainties that can be achieved in metrology laboratories based on definitive methods (Kane 1992; Kane and Potts 1997).

Isotopic compositions are also critical in these petrogenic modelling studies, to provide ages of the different magmatic episodes. Among the most important ones are 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, 143Nd/144Nd, and 147Sm/144Nd. NBS-certified isotopic reference materials are available for control of the Sr and Pb ratio measurements. USGS Columbia River basalt BCR-1 is used extensively in controlling Nd and Sm isotopics. While the material was not issued for this purpose, in 1990, approximately 50 % of all Nd isotopic ratio measurements reported in the geological literature were for BCR-1, despite the fact that, at the time, it had not been distributed by USGS for about ten years. Similarly, the La Jolla sample is used for this purpose (Wasserburg et al. 1981).

I

6.4.8 Specific Application: Petrogenic Modelling Based on Microanalysis

Microanalytical techniques are currently being used almost as extensively in petrogenic modelling studies as bulk rock methods. The lack of suitable reference materials for this application is particularly acute. Again the lack of participation by national and international metrology laboratories in resolving the problem must be noted. At this time, geochemical laboratories rely on the NIST glasses SRMs 610-617 for the purpose (Pearce et al. 1997; Kane 1998). Although the reference values available are not entirely adequate, in the absence of any alternative they provide needed support to an emerging analytical approach that is of growing importance in geochemistry (Potts 1997).

6.4.9 Application: Studies of Paleoclimates

There are a number of light stable isotope measurements that provide very important data in the study of paleoclimates to better understand and interpret anthropo- genic contributions to present-day climate change (Fritz and Fontes 1980). These measurements involve the determination of carbon and oxygen isotopes in fresh-

I 229 G. 5 References

water shells; the ratios give an indication of water temperature at the time the shells formed. Similarly deuterium in organic matter i s an indicator of paleoclimate fac- tors. The principle collection of light stable isotope ratio reference materials was first developed at NBS (Mohler 1960). These were augmented by the work of The International Atomic Energy Agency’s Consultancy Group on Stable Isotope Ref- erence Samples for Geochemical and Hydrological Investigations (Hut 1987). Important contributions include the absolute reference values of isotopic ratio standards VSMOW for hydrogen and oxygen isotopics, and Vienna PeeDee Belemite for carbon isotopics. The group has further determined isotopic values expressed as parts per thousand difference from these standards for a number of other materials. All are of value to geochemistry laboratories engaged in studies of changes in the earth’s environment over geological time.

6.4.1 0 Summary

The above discussion touches rather briefly on some key applications for the use of reference samples in geology and geochemistry. Many others could be cited, but space restrictions prohibit doing so. Regardless, it has been seen that every change in measurement capability over the past fifty years has led to new and unmet demands for reference values in natural matrix samples. These values might be for elements previously not considered measurable, or for elements at progressively lower and lower concentration ranges. As the needed reference values have become available, even when not fully up to I S 0 standards for reference value quality, geochemical interpretation of the earth’s crustal processes has moved forward, sometimes quite dramatically. Further progress i s essential, but great pride can be taken in accomplishments to date regarding reference sample production and continual data quality improvement in the geosciences.

6.5 References

AHRENS LH (1951) A story of two rocks. Geostds News1 1:157-161. ALBERTS B, BRAY D, LEWIS J , RAFF M, ROBERTS K, WATSON JD (1994) Molecular biology of the cell.

Garland, New York, Chapter 3, p 89 ff. ALCOTT GH, LAKIN HW (1975) The homogeneity of six geochemical exploration reference sam-

ples. In: ELLIOTT IL, FLETCHER WK, eds. Geochemical Exploration 1974. Proc 5th International Geochemical Exploration Symposium, pp 659-681.

ALEXANDER NM (1994) Iron. In: SEILER HG, SICEL A, SICEL H, eds. Handbook on metals in din- ical and analytical chemistry. Dekker, New York.

ANDERSON KA, TALCOTI PA (1994) Magnesium. In: SEILER HG, SIGEL A, SIGEL H, eds. Hand- book on metals in clinical and analytical chemistry. Dekker, New York.

ANDREWS LS, SNYDER R (1996) Solvents. In: KLAASSEN CD, ed. C A S A R E ~ and Doul’s Toxicology. McGraw-Hill, New York.

ANGER JP, CURTES JP (1994) Tin. In: SEILER HG, SIGEL A, SICEL H, eds. Handbook on metals in clinical and analytical chemistry. Dekker, New York.

230 6 General Application Fields

ANKE M, GLEI M (1994) Molybdenum. In: SEILER HG, SIGEL A, SIGEL H, eds. Handbook on metals in clinical and analytical chemistry, Dekker, New York.

BAEDECKER PA, ed. (1987) US Geological Survey Bulletin 1770 Methods of Geochemical Analysis, Department of the Interior, Washington DC.

BIBAK A, BEHRENS A, STURUP S , KNUDSEN L, GUNDERSEN V (1998) Concentrations of 55 major and trace elements in Danish Agricultural crops measured by inductively coupled plasma mass spectrometry. 2. Pea (Pisurn sativum Ping Pong). J Agric Food Chem 463146-3149.

BIRCH NJ, PRADGEHAM C (1994) Potassium. In: SEILER HG, SIGEL A, SIGEL H, eds. Handbook on metals in clinical and analytical chemistry. Deldter, New York.

BIRCH NJ, PRADGEHAM C, HUGHES MS (1994) Lithium. In: SEILER HG, SIGEL A, SICEL H, eds. Handbook on metals in clinical and analytical chemistry, Dekker, New York.

BLOTCKY AJ, DUCKWORTH WC, HAMEL FG (1994) Vanadium. In: SEILER HG, SIGEL A, SIGEL H, eds. Handbook on metals in clinical and analytical chemisby. Deltker, New York.

BOWMAN WS (1994). Catalogue of Certified Reference Materials, CCRMP 94-1E. Canadian Certi- fied Reference Materials Project, Natural Resources Canada, Ottawa.

BUTLER OT, HOWE AM (1999) Development of an international standard for the determination of metals and metalloids in workplace air using ICP-AES: evaluation of sample dissolution procedures through an interlaboratory trial. J Environ Monit 123-32.

B U ~ N E R J (1995) The need for accuracy in laboratory medicine. Europ J Clin Chem Clin Bio- chem 33:981-988.

CAROLI S, FORTE G, IAMICELI AL, GALOPPI B (1999) Determination of essential and potentially toxic trace elements in honey by inductively coupled plasma-based techniques. Talanta 50327-336.

CHISWELL B, JOHNSON D (1994) Manganese. In: SEILER HG, SIGEL A, SIGEL H, eds. Handbook on metals in clinical and analytical chemistry. Dekker, New York.

CHRISTENSEN JM, BYRIALSEN I<, VERCOUTERE K, CORNELIS R, QUEVAUVILLER PH (1999) Certifica- tion of Cr(VI) and total leachable Cr contents in welding dust loaded on a filter (CRM 545). Fresenius J Anal Chem: 363:28-32.

CHRISTENSEN JM, KRISTIANSEN J (1994) Lead. In: SEILER HG, SIGEL A, SIGEL H, eds. Handbook on metals in clinical and analytical chemistry, Dekker, New York.

CLARKE FW, WASHINGTON HS (1924) The composition of the earth's crust. US Geological Survey Professional Paper 127, 117 pp.

DILANA BA, LARSSON L, OHMAN S (1994) Calcium. In: SEILER HG, SIGEL A, SIGEL H, eds. Hand- book on metals in clinical and analytical chemistry. Dekker, New York.

DONAIS MI<, SARASWATI R, MACKEY E, DEMIRALP R, PORTER B, VANGEL M, LEVENSON M, MANDIC V, AZEMARD S, HORVAT M, MAY K, EMONS H, WISE S (1997) Certification of three mussel tissue standard reference materials (SRM) for methylmercury and total mercury content. Frese- nius J Anal Chem 39424-430.

DOUMAS BT, PETERS T Jr. (1997) Serum and urine albumin: a progress report on their measurement and clinical significance. Clin Chim Acta 258:3-20.

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