The opinions expressed in the following article are entirely those of the author and do not necessarilyrepresent the views of either The Royal Society of Chemistry or the Editor of The Analyst.

Perspective

Inorganic Certified Reference Materials in ‘water’What do we have, what do we need?†

Kees J. M. KramerMermayde, NL-1860 AC Bergen, P.O. Box 109, The Netherlands

An inventory was prepared of the Certified ReferenceMaterials (CRMs) available on the international marketfor the matrix ‘water’. There are different types or classesof water available, ranging from artificial (distilled,lyophilised) to more natural origin (rain-, river, lake,estuarine, sea-water). Determinants covering both majorand trace elements for each water class are summarised.The lists may suggest that most determinants/matriceshave been made available through the various suppliers ofCRMs. However, on looking at the reality of everydayanalytical performance in many routine water-testinglaboratories, the quality assurance of the analysis of asurprisingly large number of compounds is not supportedby the availability of dedicated CRMs. That these are notnecessarily obscure determinants is illustrated usingexamples from the field of environmental freshwatermonitoring practices, and from certain aspects of climateresearch analyses in the marine environment. It isconcluded that there is a need for an exchange ofinformation on the needs between the producers of CRMsand the routine analysts. This may lead to the availability,and the common use, of CRMs that support the qualityassurance of day-to-day routine analyses of water.

Keywords: Certified Reference Materials; water

Oceanic circulation is mainly driven by the density of the sea-water, which is essentially a function of temperature and theconcentration of salts it contains, the salinity. Already at the endof the 19th century, physical oceanographers realised that therewas a strong need for a means of analytical approach or, better,of calibration of their salinity measurements. The primarystandard for salinity is the potassium chloride solution, leadingto the Practical Salinity Scale which is based on conductivityand temperature.1 Based on the research carried out mainly byMartin Knudsen around the turn of the century, already in 1903the Standard Sea-Water Service was established in Christiania(now Oslo) with the task to produce and market ‘Standard Sea-water’ samples, sealed in special glass, as a primary standard forsalinity determination.20 No doubt this is the longest living andbest sold environmental (certified) reference material ever.

With this long tradition, one would have expected that in theanalysis of various aquatic compartments, freshwater or marine,the practical use of certified reference materials (CRMs) or of(laboratory) reference materials (LRMs or RMs) would besolidly in place (see, e.g., refs. 2 and 3 for definitions anduse).

Two decades ago, for all determinants except salinity, therewere no aquatic CRMs or RMs available, and hence its practicaluse was nil. Following the physical sciences, the developmentof the concept of the use of CRMs in environmental chemicalanalysis started about 25 years ago. As with so many newconcepts, for a long time the initiators and the audience were toa large extent limited to a relatively small group of experts,often from academic circles rather than from the appliedscientific and/or routine field. They were to be found inspecialised institutions (such as national bureaux of standardsand, metrological institutes) and only few institutions wereinvolved in the development of the concepts, the tools and theproduction/dissemination of the materials. Several initiatives,for example in the field of environmental monitoring, supporteda better dissemination of the knowledge on how to makeoptimum use of RMs and CRMs.4–8 However, despite theexistence of accreditation and proficiency testing schemes, theuse of CRMs was (and is!) not always widespread, certainly notto the level of the many small and medium sized (in-house)routine laboratories. This is partly due to the misunderstandingof the use of RMs versus CRMs, and therefore an over-estimation of the costs involved. RMs are intended for day-to-day use whereas, CRMs are, for example, to be used at monthlyintervals or even less.3 The (in-house made) RMs are sub-stantially cheaper than CRMs, as RMs have not been subject tocertification.

For the matrix ‘water’, the process of production and use wasalso delayed owing to the technical difficulties to be solved inthe production, the problems associated with stability andmaybe also to the homogeneity. Despite this, today we find asuite of different ‘water’ matrices on the CRM market, catering,it seems, for all requirements that we may have in the variousdisciplines of chemical analysis of waters.

This contribution discusses whether we do indeed have theCRMs that we would like to have in the aquatic analytical field,with regard to both the matrix and the determinant(s).Therefore, first an overview is presented that summarises theaquatic CRMs for sale. Then, looking from the other side, theanalyses performed in many routine (monitoring) programmeswill be checked for the availability as CRMs. If they do notmatch, then the omission(s) could be seen as an invitation to theproducers to fill the gap(s), provided, of course, that such CRMswill be feasible in terms of production, homogeneity andstability.

Aquatic CRMs available

A number of organisations provide the service of makingavailable CRMs for the matrix ‘water’. The LGC9 lists 21 RMand CRM producers, and this list may not be exhaustive. In thislist, only a limited number supply for the matrix ‘water’. Thefollowing CRM water producers have been identified: Euro-

† Presented at the DG12 Workshop on Quality Control of Water Analysis, Lisbon,Portugal, June 18–19, 1997.

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pean Commission Reference Bureau of Standards (BCR,Belgium), International Atomic Energy Agency (IAEA, Aus-tria), National Institute for Standards and Technology (NIST,USA), National Research Centre for Certified ReferenceMaterials (NRCCRM, China), National Research Council(NRC, Canada), National Water Research Institute (NWRI,Canada) and, for IAPSO, the Standard Sea-water Service (UK).Almost all address inorganic constituents only and there arehardly any aquatic CRMs for organic constituents. The fewexceptions so far are certified for dissolved organic carbon(DOC) or pesticides.10

An overview of the Certified Reference Materials that are onthe international market is given in Table 1. To compile thistable the catalogues from the suppliers mentioned above,overviews and brochures were used.9,11–15

In Table 1, a distinction is made according to the name theproducers gave to their products. For example, only a fewmention only the matrix term ‘water’; usually there is a furtheridentification, such as ‘distilled’, or a type of natural origin, e.g.,‘natural’ or, more specific, ‘rain-’, ‘ground-’, ‘river’, ‘lake’ or‘sea-water’. Sometimes the location of sampling (near-shore,open ocean) is added to the name. Even freeze-dried (lyophi-lised) water has recently become available. A number of CRMsdo not contain the natural concentrations; they have beensubjected to additions (fortified); they may be a mixture(composite) or made for a purpose (simulated). For freshwaters, distinctions are sometimes made that lead to a range inthe hardness of the waters used.

In the second column of Table 1, the analytes are presented.Asterisks indicate that the name as provided by the supplier hasbeen abbreviated in this list for layout reasons. Categories fall ingeneral into two areas: trace elements and major elements/nutrients. The latter are sometimes supplied in both high andlow contents owing to the large differences found in nature. Thethird column provides the catalogue name and, the last columnthe producer.

An inventory of the determinants for these CRMs ispresented in the Tables 2 and 3. It seems that a wide variety ofanalyses are already covered. This is especially true for themajor elements in the matrices rainwater, lake water and, to alesser extent, river water, where we often found more than onesupplier. For trace elements only river water, estuarine waterand sea-water are covered to a reasonable extent but, except forsea-water, they are available from one producer only. Thecolumn Distilled/fortified consists in many cases of single-element CRMs.

At first glance, the coverage of the field seems reasonablywell filled for the major elements. The distinction between lakewater and river water may be artificial, and ‘natural’ water isundefined in this respect. Most determinants seem to be coveredfor the full range of aquatic matrices. A closer look, however,reveals some interesting observations (note that the capital Xdenotes availability with certified values and the lower-case x inparentheses identifies only recommended values).

For the major elements (Table 2), we see, for example, that:acidity is certified only for rainwater (this may be not surprising,because of the past boom in acid rain research); total carbondioxide, important in climate research, is not available as aCRM (only for sea-water and only recommended values);bromide (bromate) and iodide are not certified yet (expectedsoon for groundwater); for phosphate, only for estuarine wateris a CRM is available; all other materials provide recommendedvalues only; for boron, only materials with recommendedvalues are available; for sea-water and estuarine water, very fewof the major determinants are certified. Of course, a number ofthem are not of interest owing to the high salt content and theconstant ratios between the major elements in sea-water.However, considering the very large number of, e.g., nutrientanalyses carried out in the marine environment, it is surprising

to have no CRMs available for (total) N and P, nitrate, nitrite orsilicate; there are no CRMs for the relatively large market of

Table 1 Overview of inorganic CRMs for the matrix ‘water’

Water type Analyte(s) Catalogue Producer†

Lyophilised water—— CrIII/VI, Cr CRM544 BCR— Pesticides CRM606 BCR

Distilled water—Fortified Major elements* ION-92 NWRI

Water—— 2H IAEA-302 IAEA— 18O IAEA-304 IAEA— Anions GBW08606 NRCCRM— Single trace elements* GBW086xx NRCCRM— Metal elements GBW08608 NRCCRMFortified Trace metals TM-23–28 NWRIFortified Trace metals TM-DA-51–54 NWRI

Natural water—Composite,

naturalcoloured

Major elements ION-94 NWRI

— Mercury SRM1641c NIST— Trace elements (SRM1640)‡ NIST— Trace elements SRM1643d NIST

Rainwater—Simulated Major elements, salts

(low)CRM408 BCR

Simulated Major elements, salts(high)

CRM409 BCR

Simulated Major and traceelements*

SRM2694a NIST

Simulated Major elements GBW08627-9 NRCCRMCentrifuged Major elements* GRM-02 NWRI

Groundwater—Artificial major elements (high,

low)(CRM616-617)‡ BCR

Natural trace elements (high,low)

(CRM609-610)‡ BCR

Natural Br (high, low) (CRM611-612)‡ BCRFreshwater—

— Nitrate (low) CRM479 BCR— Nitrate (high) CRM480 BCR— Major elements (low) CRM398 BCR— Major elements (high) CRM399 BCR

Lake water—Fortified Major elements* ION-20 NWRIMedium hard Major elements* ION-95 NWRISoft Major elements* ION-911 NWRISoft natural Major elements* AUD-6 NWRISoft Major elements* HURON-03 NWRI

River water—Hard Major elements* ION-911 NWRIMedium hard Major elements* SOUR-01 NWRI

Estuarine water—— Trace elements SLRS-3 NRC— Trace elements CRM505 BCR— Trace elements SLEW-2 NRC

Sea-water—— Salinity Standard sea-

waterSSS

— Nutrients (low) OSI-LNS ?— Trace elements CRM403 BCR— Mercury CRM579 BCR

Near shore Trace elements CASS-3 NRCOpen ocean Trace elements NASS-4 NRC

* See text. † BCR, European Commission Reference Bureau ofStandards (Belgium); IAEA, International Atomic Energy Agency(Austria); NIST, National Institute for Standards and Technology (USA);NRC, National Research Council (Canada); NRCCRM, National ResearchCentre for Certified Reference Materials (China); NWRI, National WaterResearch Institute (Canada); SSS Standard Seawater Service (UK).‡ Submitted to the BCR Certification Committee.

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Table 2 Major 'elements' in water. Each capital X denotes that a certified value is available; lower-case (x) denotes that only recommended values areprovided

Lyophilised Distilled/fortified Natural Ground Rain Fresh Lake River Estuarine Sea

pH X X XXXX XXXXX XXConductivity X X XXXX XXXXX XXSalinity XAcidity XXXXAlkalinity X X XXXXX XXTotal CO2 (x)Turbidity X X X XXXXX XXColour X X X XXXXX XXF X XXXXX XXXXX XXCl XX X X* XXXXX X XXXXX XXBr X*

INO3 X (x) X* XXXXX X X XNO3 + NO2 X X X XXXXX X(x) XNH4 X X XXXXX XX(x)XX (x)(x)Total Kjeldahl

nitrogenX X X XXXXX XX

PO4 (x) X (x) (x)(x) (x)(x) XSi X X XXXXX XX XSO4 XX X X* XXXXX X XXXX XXHardness X X X XXXXX XXK X X XXXXX X XXXXX XXXNa X X X* XXXXX X XXXXX XXXCa X X X* XXXXX X XXXXX XXXMg X X X* XXXXX X XXXXX XXXB (x) (x)(x) (x)(x)DOC X X X XXXXX XXPesticides XDIC X X X XXXXX XX

* Submitted to the BCR Certification Committee.

Table 3 Trace elements in water. Each capital X denotes that a certified value is available and lower-case (x) denotes that only recommended values areprovided

Lyophilised Distilled/fortified Natural Ground Rain Fresh Lake River Estuarine Sea

Ag (x)Al X X X* X X XX X (x)As X X* X X (x)XXBa X XBe X XBi (x)Cd XX X* X XX XXXCo X X X XXCr XX X X XXCrIII/VI XCu XX X* X XX XXXFe X X* X X X XXHg X X XLaLi (x)XMn X X* X X X XXMo X X (x) XXXNi XX X XX XXXPb XX X* X X XXXSb X XSe X X(x)Sn (x)Sr X (x)Ti (x)U (x) (x) (x) X(x)V X X (x)Zn XX X X XXX

* Submitted to the BCR Certification Committee.

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mineral waters (public health concern), with their often specificcharacteristics in ‘mineral’ content.

If we have a look at the natural waters for the trace elements(Table 3) we find: aluminium, iron and manganese arerepresented in a wider set of matrices (again, probably becauseof the acid rain related activities); silver, bismuth, tin, titaniumand uranium are provided only as recommended values(uranium in sea-water has been certified); neither certified norrecommended values are available in an aquatic matrix for therare earth elements (given as lanthanum in the table) and allother elements not on the list (such as Au, Cs, Ga, Ge, In, Ir, Os,Pd, Pt, Rh, Ru, Sc, Ta, Tl, Tc, W, Y, Zr).

Of course, the question of whether we really need CRMs forthese more ‘obscure’ elements such as In, Rh, Tc or Zr may beasked. However, on the other hand, most of the elements listedas not available as aquatic CRMs, are widely and increasinglyused in today’s industry, e.g., in electronic components and incatalysts. The reality is that if there are no regulations or policydemands for such elements (or other compounds), there is,except for fundamental scientific work, hardly any interest fromthe side of chemical analysts to analyse aquatic media for them.As a consequence, it is unlikely that there will be a market forthese products, unless the less favoured elements are certified inaddition to the more common elements in a multi-elementCRM. As the production and homogeneity/stability testingcosts often dominate the definition of the price of CRMs, thecertification of the less common elements during production orin existing CRMs should be supported.

Do we need more aquatic CRMs?

Can we say, therefore, that all routine environmental analyses inwater are covered by one or more reference materials thatprovide certified or at least recommended values? In order toanswer this question, we should look in more detail at the suiteof analyses that are performed in the day-to-day reality of(routine) laboratories in the ‘water’ field.

Important reasons for the analysis of water include: supportfor (EC) directives (environmental quality, drinking water,bathing water, aquaculture); national policy-related objectives(monitoring programmes for groundwater, freshwater, marinewaters); fundamental/applied research (for example, climateprogrammes, acid rain programmes).

The variety of objectives leads automatically to a wide suiteof determinants that may require suitable CRMs. Obviously, forbathing water or sea-water there will be a different set ofdeterminants than for drinking water (the latter usually require,e.g., the determination of more than 100 pesticides and relatedsubstances). As an illustration, this contribution focuses in moredetail on (surface) water quality objectives for Europe. This isan area of analytical activity that requires large numbers ofsamples to be collected and analysed daily.

The (draft) EC water quality objective,16 intended to providea classification of ecological freshwater quality, requires thefollowing variables to be monitored:(A) oxygen regime

(O2 dissolved, saturation; BOD5; COD-Mn);(B) eutrophication parameters

(total N, total P, chlorophyll a);(C) acidification

(pH);(D1) heavy metals and cyanide

(Al, As, Cd, CrVI, Cu, Pb, Hg, Ni, Zn, CN);(D2) other harmful substances

(dieldrin, chlordane, DDT and metabolites, endrin,heptachlor, lindane, malathion, parathion, PCP,PCBs, toxaphene);

(E) radioactivity(not yet specified);

(F) microbiological parameters(faecal coliforms, faecal streptococci).

Before commenting, we can expand this EU list to a morecomplete list that covers Europe at large, by including theparameters to be monitored in the countries of the Danube riverbasin (totalling 11 countries, from its source in Germany to themouth in the Black Sea). All variables that have to be measuredby the national monitoring programmes in these countries of theDanube river basin17 have been summarised. The following listis a sum of all parameters for the 11 countries (individualcountries will usually have a selection only), and is to be read asbeing additional to the list for EU countries mentioned above.

Additional water quality parameters for Danubian countriesare: temperature; conductivity; alkalinity; TOC, DOC, phyto-plankton biomass; hardness, Ca, Mg, CO3

22, HCO32, CO2; Fe,

Mn, Ag, B, Ba, Be, Mo, Se, U, V, 226Ra; K, Na, Cl2, SO422,

free residual Cl2, H2S, S22; suspended particulate matter,turbidity, transparency; colour, odour; surfactants; non-polarextractable organic compounds, total organochlorines.

Taking the two lists together, a comparison with Tables 2 and3 indicates that many parameters have so far been covered bycertified RMs, or at least with recommended values. Keeping inmind that these analyses are obliged to be carried out throughnational and/or international legislation, it is surprising to seethat a number of the analyses are still not supported by CRMs,such as: total organic carbon (TOC), biological and chemicaloxygen demand; chlorophyll a; the carbonate system (CO3

22,HCO3

2, CO2, total CO2); cyanide; sulfur species, other thansulfate; except for seven pesticides, all organic compounds,including surfactants.

Another example of a field with large numbers of samples tobe analysed is climate research. Climate research often involvesmulti-national (marine) monitoring and research programmeswith a wide variety of processes studied. They involve, forexample, the production of biomass [nutrients, dissolved andparticulate organic carbon (DOC, POC), chlorophyll a and thepigment spectrum], the carbon dioxide system and other tracegases (such as dimethyl sulfide). Tracers (or, e.g., isotope ratios)are commonly used in climate research. Examples include 39Ar,226,228Ra, 222Rn, 228,230Th, 3H, 3He, 13C/12C, 14C/12C and 18O/16O. Hardly any of these determinants has been covered by asuitable CRM.

It may be surprising that despite the very large number ofanalyses carried out routinely all over the world, so many CRMsare not available. Several reasons for this ‘omission’ can beidentified.

First, there may be a practical problem, in that there has notbeen developed a suitable method to produce a certain materialthat can be used as a CRM, e.g., owing to sampling problems,problems with homogeneity, stability, or certification. Thedemand for (ultra) trace concentrations, and consequently thehandling of (very) large volumes during preparation, placepractical limitations on the production of many liquid CRMs for(in)organic constitutuents. In addition, especially the long-termstability (related to the shelf-life of the material) poses problemsin many cases. At present it is not realistic to ask for CRMs for,e.g., H2S and sulfide, free residual chlorine or cyanide, as thereseem to be too large practical constraints. However, thedevelopment and/or application of new approaches, such aslyophilised solutions (Dyg et al.18 for CrIII/VI; Barcelo et al.,19 forpesticides) or the development of single-use CRMs has led tothe preparation of CRMs that were thought not possible in thepast.3 The lyophilisation approach could possibly even beextended to bacteria in water matrixes. Also, the feasibility ofthe development of dedicated preservatives needs furthertesting.

Second, the use of CRMs (and LRMs) is an approach that,despite their availability for over 20 years, has not alwaysreceived attention by an audience beyond the (scientifically/

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metrologically oriented) analytical chemists. It takes time fortypically field-oriented and (in-house) routine laboratories toadapt their standard methodologies (‘we have done theseanalyses for years, hence our analyses are OK’).

Third, education and dissemination of the knowledge on howto use LRMs and CRMs could be better developed. Even todaymany analysts argue that they cannot use reference materialsbecause they are too expensive (meaning that they cannot useCRMs as LRMs). The use of LRMs and CRMs is not yet astandard part of analytical thinking in all laboratories.

Finally, it seems that the selection of the aquatic CRMsavailable today is to a considerable extent the responsibility ofproducers rather than of (potential) users. The lack of traditionin the use of CRMs with many users is certainly one of thereasons for the less favourable communication.

In conclusion, there are a number of CRMs available todayfor the analysis of inorganic compounds in the matrix ‘water’.Despite this, there seem to be many routine analyses (e.g., in thefield of environmental quality control) that are as yet notsupported by the availability of CRMs. If analysts active in thefield of (routine) chemical analysis became more aware of theneed and the advantages of the use of CRMs in their qualityassurance schemes, they might request more proactively theavailability of certain CRMs (and LRMs). It will be the task ofthe producers/suppliers of CRMs to listen to the needs of thoseactive in practical (routine) analytical work. Certainly not least,it will be the task of the entire analytical chemical community todisseminate further relevant information on the adequate use ofLRMs and CRMs.

References

1 The Practical Salinity Scale 1978 and the International Equation ofState of Seawater 1980, Technical Papers in Marine Science, No. 36,UNESCO, Paris, 1981.

2 Terms and Definitions Used in Connection with Reference Materials.ISO Guide 30. International Organization for Standardization,Geneva, 1992.

3 Quevauviller, Ph., and Maier, E. M., Production of CRMs forEnvironmental Matrices, Report No. EUR 18157EN of the European

Commission, ed. Kramer, K. J. M., EC-SM&T Programme, EuropeanCommission, Brussels, 1998.

4 Vijverberg, F. A. J. M. and Cofino, W. P., Control Procedures: GoodLaboratory Practice and Quality Assurance, ICES Techniques inMarine Environmental Sciences, No. 6, ICES, Copenhagen, 1987.

5 Reference Methods and Materials: a Programme of Support forRegional and Global Marine Pollution Assessments, in UNEP/IAEA/IOC Report, UNEP, Nairobi, 1990.

6 Griepink, B., Maier, E. A., Quevauviller, Ph., and Muntau, H.,Fresenius’ Z. Anal. Chem., 1991, 339, 599.

7 Hamilton, E.I., Mar. Pollut. Bull., 1991, 22, 51.8 Marschal, A., Calibration of Chemical Analyses and Use of Certified

Reference Materials, Draft ISO Guide 32, ISO/REMCO N262 Rev.,International Organization for Standardization, Geneva, 1993.

9 The Office of Reference Materials. Certified Reference MaterialsCatalogue, Issue No. 3, Laboratory of the Government Chemist,Teddington, 1997.

10 Wise, S. A., Schantz, M. M., Parris, R. M., Rebbert, R. E., Benner, B.A., and Gills, T. E., 1992, 20, M57; Wells, D. E., Analyst, 1998, 123,983.

11 Standard and Reference Materials for Marine Science, rev. edn., IOCManuals and Guides, No. 25, UNESCO, Paris, 1993.

12 Analytical Quality Control Services (AQCS), Intercomparison Runswith Reference Materials, IAEA, Vienna, 1992.

13 Survey of Reference Materials for Trace Elements. Environmentaland Biological matrices. IAEA TecDocs 854 and 880 [(paper andInfoSelect Database (diskette)], IAEA, Vienna, 1996.

14 Rasberry, S. D., Worldwide Production of Certified ReferenceMaterials, ISO/REMCO, Status Report, International Organizationfor Standardization, Geneva, 1994.

15 BCR Reference Materials 1997. Institute for Reference Materials andMeasurements (IRMM/MRM), Geel, 1997.

16 ECE Standard Statistical Classification of Ecological FreshwaterQuality (Draft). CES 668/1990, 1990.

17 Water Quality Targets and Objectives for Surface Waters in theDanube Basin. Project EU/AR/203/91, Inception Report, VITUKI,Budapest, 1995.

18 Dyg, S., Cornelis, R., Griepink, B., and Quevauviller, Ph., Anal.Chim. Acta, 1994, 286, 297.

19 Barcelo, D., House, W. A., Maier, E. A. and Griepink, B., Int. J.Environ. Anal. Chem., 1994, 57, 237.

20 Wallace, W. J., The Development of the Chlorinity/Salinity Conceptin Oceanography, Elsevier, Amsterdam, 1974.

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