CCQM-K49 Key Comparison Essential and Toxic Elements in … · Thiago de Oliveira Araujo NRC Canada – Christine Scriver and Ralph Sturgeon NIM (China) – Jun Wang LNE (France)

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CCQM-K49 Key Comparison

Essential and Toxic Elements in Bovine Liver

Draft B - Final Report

June 2, 2008

Robert R. Greenberg

Analytical Chemistry Division

Chemical Science and Technology Laboratory National Institute of Standards and Technology

Gaithersburg, MD 20899-8395, USA

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With Contributions From:

INTI (Argentina) – Liliana Valiente and Margarita Piccinna NMIA (Australia) – Lindsey Mackay INMETRO (Brazil) – Maria Cristina Baptista Quaresma, Gaspar Barbosa Alexandre and Thiago de Oliveira Araujo NRC Canada – Christine Scriver and Ralph Sturgeon NIM (China) – Jun Wang LNE (France) – Guillaume Labarraque and Caroline Oster BAM (Germany) – Jochen Vogl, Wolfgang Birke, and Gundel Riebe PTB (Germany) – Reinhard Jaehrling and Olaf Rienitz HKGL (Hong Kong) – W. C. Sham and Y. C. Yip INRIM (Italy) – Luigi Bergamaschi NIMJ (Japan) – Kazumi Inagaki KRISS (South Korea) – Euijin Hwang and Yong-Hyeon Yim TUBITAK (Turkey) – Serpil Yenisoy Karakas, Oktay Cankur and Duran Karakas LGC (UK) – Ruth Hearn, Sheila Merson and John Entwisle. IAEA (UN) – András Törvényi, and Ales Fajgelj NIST (US) – Rolf Zeisler, Elizabeth Mackey, Rabia Spatz, Karen Murphy, and Mike Winchester

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1. Abstract A Key Comparison (CCQM-K49) of the determination of toxic and essential elements in bovine liver has been conducted under the auspices of the CCQM Inorganic Analysis Working Group (IAWG). All elements were present at naturally occurring levels, and in naturally occurring (non-spiked) forms in this material. Sixteen National Metrology Institutes (NMIs) submitted data for this study using a variety of analytical methods. Measurands for this study consisted of elements that were expected to be relatively easy to determine (Fe and Zn), moderately difficult to determine (Se, Cd and Pb), and very difficult to determine (Cr and As). The results of this comparison seem to bear these rankings out, with the possible exception that Se was more difficult to determine than Cd and Pb, perhaps due to the difference in the amount of experience for many NMIs with this element compared to Cd and Pb. However, Se seemed to be less difficult to determine than Cr and As based on the dispersion of the reported data and the typical expanded uncertainties reported by the NMIs. Results for this Key Comparison are highly encouraging in that all reported values, with only three exceptions, agreed within stated (expanded) uncertainties with the Key Comparison Reference Values (KCRVs), or were within an additional 1 % of the KCRV. Since this Key Comparison included 60 separate determinations of the studied constituents, 95 % of the results could be considered successful. 2. Introduction Accurate determination of toxic and essential elements in a food matrix is important for health and nutritional, as well as for environmental purposes. Beef liver is an important food source for many people around the world, and provides significant amounts of many essential elements. However, depending upon environmental conditions, bovine, and other animal livers (including human livers), can accumulate high levels of potentially toxic elements. The capability to accurately determine the content of the toxic elements is therefore important from toxicological and environmental viewpoints. A Key Comparison (CCQM-K49) and a parallel Pilot Study (CCQM-P85) of the determination of toxic and essential elements in bovine liver were conducted under the auspices of the CCQM Inorganic Analysis Working Group (IAWG). Seven elements were selected for this study: Fe, Zn, Se, Cd, Pb, Cr and As. Iron and Zn should be relatively easy to determine since their mass fractions are high, hundreds of mg/kg, and the matrix is relatively easy to dissolve. Selenium, Cd and Pb provide more of a challenge since their levels are lower, a few mg/kg for Se and slightly less than 0.1 mg/kg for Cd and Pb. However, Cd and Pb are frequently determined at these levels, and so analysts are likely to have more experience with these elements than with Se. Chromium and As present significant challenges. Both elements are at relatively low levels (several tens of µg/kg), and both are susceptible to volatility losses. In addition, blanks for Cr can be quite significant. All elements were present at naturally occurring levels, and in naturally occurring (non-spiked) forms in this material. A Pilot Study (CCQM-P85) of the same material has been run concurrently with CCQM-K49. Many of the CCQM-K49 participants have submitted results for additional elements to CCQM-P85, as well have some outside expert laboratories. In addition, the IAWG has designated the combined Key Comparison and Pilot Study as a “exemplary study” and requested that all NMIs with analytical capabilities for inorganic constituents in the matrix

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under investigation participate and submit results for Fe and Zn. The goal of this exemplary study was to enable comparison among a large portion of the NMIs in a single study, which has been difficult since the large number of studies currently being undertaken has resulted in a limited number of the NMIs participating in any single study. Results for the exemplary study will be presented in the report for CCQM-P85. 3. Participation in CCQM-K49 Sixteen NMIs registered and submitted results for CCQM-K49. Participants are listed in Table 1. 4. Samples The bovine liver for this study is the same material that will subsequently be certified as NIST SRM 1577c. Liver tissues were collected from 31 steers that were slaughtered at Texas A&M University School of Veterinary Medicine. The animals were slaughtered for the purpose of teaching students bovine anatomy and how to butcher. The meat from these animals was prepared for retail under the supervision of a State of Texas meat inspector to ascertain the health of each animal. Titanium bladed, Teflon handled knives were used for all tissue processing. The knives were rinsed with HPLC-grade water between livers and with HPLC-grade water and 95% alcohol at the end of each day. The thin fibrous tissue encapsulating each liver was removed when possible, as were other connective tissues, hepatic arterial tissue and large bile duct tissues. The livers were cut into 5 cm cubes and placed in Teflon bags; each liver yielded between 4 and 5 kg of processed tissue. The Teflon bags, containing the livers, were sealed, labeled, placed in plastic zip-lock bags, and stored in a walk-in meat freezer at approximately -20 C. The samples were shipped on dry ice to NIST the following week. Total liver collected was ≈ 120 kg (fresh weight). The tissue was homogenized at NIST with a food processor equipped with titanium blades. The resulting paste was poured into glass trays, frozen, and lyophilized. The dry material was blended in the food processor and then jet-milled. The resulting final product was radiation sterilized, bottled in 1640 20-g units and 200 5-g units, and stored at room temperature.

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Table 1. Participants in CCQM-K49, and Elements Registered

Institute Country Elements Registered

INTI Instituto Nacional de Tecnología Industrial

Argentina

Fe, Zn

NMIA National Measurement Institute, Australia

Australia

Fe, Zn, Se, Cd, Pb, As

INMETRO Inst. Nacional de Metrologia, Normalização e Qualidade Industrial

Brazil Fe, Zn, Pb, Cr

NRC National Research Council

Canada Fe, Zn

NIM Institute of Metrology P. R. China

China Fe, Zn, Se, Cd, Pb, Cr, As

LNE Laboratoire National de Métrologie et d'essais

France Fe, Zn, Cd, Pb

BAM Bundesanstalt für Materialforschung und -prüfung

Germany Zn, Cd

PTB Physikalisch-Technische Bundesanstalt

Germany Fe, Pb, Cr

HKGL Hong Kong Government Laboratory

Hong Kong Fe, Zn

INRIM National Institute of Metrological Research

Italy Fe, Zn, Se

NMIJ National Metrology Institute of Japan

Japan Fe, Zn, Cd, Cr

KRISS Korea Research Institute of Standards and Science

South Korea Fe, Zn, Se, Cd, Pb

TUBITAK UME TUBITAK National Metrology Institute

Turkey Cd, Pb, Cr, As

LGC Laboratory of the Government Chemist

United Kingdom

Fe, Zn, As

IAEA International Atomic Energy Agency

United Nations

Fe, Zn, Se, Cd, Pb, Cr, As

NIST National Institute of Standards and Technology

United States of America

Fe, Zn, Se, Cd, Pb, Cr, As

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5. Instructions A minimal set of instructions was sent to each participant by the coordinating laboratory. Because lyophilized bovine liver tissues are somewhat hygroscopic, it was recommended that moisture determinations be made on separate test portions taken at the same time as the portions to be analyzed. The recommended procedure is drying to constant mass at room temperature in a desiccator over fresh, anhydrous CaSO4 (e.g., DRIERITE®). This usually requires a minimum of 10 days. A sample size of 100 mg or larger is recommended for analysis. It was suggested that at least five replicate samples be analyzed in order to provide an opportunity to assess the impact of measurement replication on the overall analytical uncertainty. Participants were asked to provide the following information:

1. a complete description of the analytical methodology, including all relevant equations used

2. complete uncertainty budgets with all potential uncertainty components assessed for each measurand

3. individual values determined for the amount content or mass fraction of each measurand in each of the analytical portion measured

4. a single best-estimate of the amount content or mass fraction for each measurand in the comparison material (such as mean, weighted mean etc.)

5. a combined standard uncertainty for each measurand 6. an expanded uncertainty for each measurand 7. the k-value used to calculate the expanded uncertainty for each measurand 8. either one table for all elements or tables for each element summarizing the

information requested for items 4-7 6. Methods No method was prescribed for these analyses, however it was recommended that methods used be capable of achieving an expanded uncertainty of less than 5%. Sample digestion methods also were not prescribed; however, for methods requiring sample digestion, participants were cautioned about potential analyte loss, especially with dry-ashing techniques. Methods used in this study are listed in Table 2.

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Table 2. Analytical Methods used for CCQM-K49 Institute Dissolution Method Instrumental Method Calibration Method

INTI Microwave (HNO3/H2O2) FAAS External Standard Calibration

NMIA Microwave (HNO3/H2O2) ID-ICPMS Isotope Dilution

INMETRO Microwave (HNO3) ICPMS External Standard Calibration

NRC Microwave (HNO3/H2O2) ICPOES External Standard Calibration

NIM (China) Microwave (HNO3/H2O2)

Microwave (HNO3/H2O2)

ID-ICPMS - except As

ICP-MS - As

Isotope Dilution

External Standard Calibration

LNE Microwave (HNO3/H2O2) ID-ICPMS Isotope Dilution

BAM Microwave (HNO3) ID-TIMS Isotope Dilution

PTB Open/Quartz (HNO3)

Microwave (HNO3/H2O2)

ID-ICPMS - Cr

ID-ICPMS - Fe, Pb

Isotope Dilution

Isotope Dilution

HKGL Microwave (HNO3/H2O2) ID-ICPMS Isotope Dilution

INRIM None INAA Comparator Method

NMIJ MW (HNO3,HClO4,HF) ID-ICPMS Isotope Dilution

KRISS Open/Microwave (HNO3) ID-ICPMS Isotope Dilution

TUBITAK UME Microwave (HNO3) ICPMS Standard Additions

LGC Microwave (HNO3)

Microwave (HNO3)

ID-ICPMS - Fe, Zn

ICPMS collision cell - As

Isotope Dilution

Standard Additions

IAEA Microwave (HNO3/H2O2) ICPMS External Standard Calibration

NIST None

Open (HNO3/HF/HClO4)

Open/Microwave (HNO3)

Microwave/Open (HNO3)

INAA - Cr, Fe, Zn, Se

RNAA - As

ID-ICPMS - Zn, Cd, Pb

ICP-OES - Fe, Zn

Comparator Method

Comparator Method

Isotope Dilution

Standard Additions

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7. Results The participants’ results are summarized in Table 3-9. The Mixture Model Probability Density Function (MM-PDF) developed by David Duewar (applied using PDFMaker) was used to evaluate the data for each element in this study. At INMETRO’s request, their data for all elements were excluded from the KCRV calculation in view of instrument problems they observed after the measurement results were submitted. Note that although Tables 3-9 show the NIST results for multiple analytical techniques, only the single NIST combined value was used for data evaluation using PDFMaker. Graphical representations of the data (direct output of PDFMaker) are provided in Fig. 1-7. The Mixture Model Median was selected as the Key Comparison Reference Value (KCRV) for each constituent and the U95%-location (from PDFMaker) was selected as the Key Comparison Reference Uncertainty (KCRU). The KCRV and KCRU for each of the seven elements for this study are listed in Table 10, along with an estimate of the between-lab dispersion (sMMshorth). Another view of the results is presented graphically in Fig. 8-14. As expected, agreement among the labs was very good for Fe and Zn. Despite relatively small KCRUs (approximately 1% for both elements), all NMIs agreed with the KCRV within stated (expanded) uncertainties, with the exception of INMETRO for Fe, and NIM (China) for Zn. In fact, the Zn result for NIM (China) was within 0.7% of overlapping the KCRV with its expanded uncertainty. After discussion of the results of this study at the April 2007 meeting of the IAWG, NIM (China) found a problem with the calibration factor for the mass bias of the MC-ICP-MS for Zn. After correcting this problem, their measurement result of Zn in CCQM-K49 becomes 180.1 mg/kg ± 1.3 mg/kg (k=2). NIM's results presented in Tables 4 and 12, and in Figures 2 and 9, use the originally reported values. Agreement among NMIs was also very good for Cd and Pb. Again the KCRU was relatively small, about 2%. All NMIs agreed with the KCRV for Pb, within expanded uncertainties, with the exception of INMETRO. Although both LNE and TUBITAK UME missed agreeing with the KCRV for Cd, the LNE value missed overlap (within expanded uncertainties) by only 0.4%. It should be noted that the actual Cd mass fraction in the study material (KCRV = 97.6 µg/kg) turned out to be slightly higher than the estimated concentration that was listed in the measurement protocol (20 µg/kg to 80 µg/kg). Although it was expected that Se would not present too much of a challenge, only a relatively few (5) NMIs participated for this element. Although results for all NMIs agreed with the KCRV within expanded uncertainties, the KCRU was relatively larger (3.7%) than the previous four elements. Chromium and As were clearly difficult to determine. Only five NMIs participated for each of these elements, and the magnitude of the KCRUs was relatively high (6-7%). In addition, the expanded uncertainties for most of the participating labs were typically larger than for the previously discussed elements. However, it is encouraging to note that the results for all participating NMIs agreed with the KCRV, within stated uncertainties. Four NMIs did not submit results for one or two of the registered elements including: IAEA – Zn and Cr INMETRO – Cr KRISS – Se and Cd NMIA – As

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Table 3. Measurement Results Reported by Individual NMIs/Laboratories for Fe in CCQM-K49

Participant Reported Value

(mg/kg)

Expanded Uncertainty

(mg/kg)


(%)

number of samples

k value

INTI (Argentina) 209 14 3.7 3 2.0

NMIA (Australia) 198.1 8.2 4.1 6 2.06

INMETRO (Brazil) 151.6 8.2 5.4 5 2.0

NRC (Canada) 207 9.1 4.4 8 2.0

NIM (China) 194.33 1.13 0.6 6 2.0

LNE (France) 196 3 1.5 5 2.0

PTB (Germany) 199.3 2.2 1.1 8 2.0

HKGL (Hong Kong) 199.2 4.8 2.4 5 2.0

INRIM (Italy) 206.7 8.1 3.9 6 2.0

NMIJ (Japan) 199.1 3.3 1.7 5 2.0

KRISS (South Korea) 197.78 0.68 0.3 5 2.04

LGC (UK) 197.5 3.8 1.9 9 2.0

IAEA (UN) 194 6 3.1 5 2.0

NIST (USA, Combined) 197.1 2.3 1.2 25 2.0

NIST – INAA 198.23 2.96 1.5 36 2.0

NIST – ICPOES 195.8 1.2 0.6 11 2.11

KCRV 198.1 2.2 1.1

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Table 4. Measurement Results Reported by Individual NMIs/Laboratories for Zn in CCQM-K49


(mg/kg) Expanded

Uncertainty (mg/kg)


(%)

number of samples

k value

INTI (Argentina) 175 9 5.1 3 2.0

NMIA (Australia) 182.1 6.2 3.4 6 2.06

INMETRO (Brazil) 181.1 4.8 2.7 5 2.0

NRC (Canada) 183 7.4 4.0 8 2.0

NIM (China) 177.6 1.21 0.7 6 2.0

LNE (France) 181 3 1.7 6 2.0

BAM (Germany) 184.4 1.0 0.5 6 2.0

HKGL (Hong Kong) 181.7 4.9 2.7 6 2.0

INRIM (Italy) 187.8 7.9 4.2 6 2.0

NMIJ (Japan) 182.6 3.7 2.0 5 2.0


LGC (UK) 182.0 4.2 2.3 12 2.0

IAEA (UN) NR*


NIST – INAA 180.02 2.63 1.5 25 2.0

NIST – IDICPMS 181.9 1.2 0.7 6 2.0

NIST – ICPOES 179.99 0.53 0.3 11 2.0

KCRV 181.9 1.9 1.0 * Indicates that this NMI registered for this element but did not submit data

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Table 5. Measurement Results Reported by Individual NMIs/Laboratories for Se in CCQM-K49


(mg/kg) Expanded

Uncertainty (mg/kg)


(%)

number of samples

k value

NMIA (Australia) 2.07 0.11 5.3 6 2.03

NIM (China) 2.067 0.027 1.3 6 2.0

INRIM (Italy) 2.02 0.06 3.0 6 2.0

KRISS (South Korea) NR*

IAEA (UN) 2.17 0.06 2.8 5 2.0

NIST (USA, INAA) 1.993 0.035 1.8 25 2.0

KCRV 2.056 0.077 3.7 * Indicates that this NMI registered for this element but did not submit data Table 6. Measurement Results Reported by Individual NMIs/Laboratories for Cd in CCQM-K49


(mg/kg) Expanded

Uncertainty (mg/kg)


(%)

number of samples

k value

NMIA (Australia) 0.1000 0.0062 6.2 6 2.18

NIM (China) 0.0975 0.0015 1.5 6 2.0

LNE (France) 0.0930 0.0026 2.8 6 2.0

BAM (Germany) 0.0978 0.0006 0.6 6 2.0

NMIJ (Japan) 0.0963 0.0021 2.8 5 2.0

TUBITAK UME (Turkey) 0.110 0.0025 2.3 5 2.0

IAEA (UN) 0.099 0.003 3.0 5 2.0


NIST – RNAA 0.0961 0.0022 2.3 7 2.0

NIST – IDICPMS 0.0971 0.00081 0.8 6 2.0

KCRV 0.0976 0.0016 1.6

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Table 7. Measurement Results Reported by Individual NMIs/Laboratories for Pb in CCQM-K49


(mg/kg) Expanded

Uncertainty (mg/kg)


(%)

number of samples

k value

NMIA (Australia) 0.0639 0.0037 5.8 6 2.12

INMETRO (Brazil) 0.05046 .000090 1.8 5 2.0

NIM (China) 0.0615 0.0042 6.8 6 2.0

LNE (France) 0.062 0.0014 2.3 6 2.0

PTB (Germany) 0.0624 0.0021 3.4 8 2.2



IAEA (UN) 0.0586 0.0030 5.1 5 2.0

NIST (USA, IDICPMS) 0.06282 0.00092 1.5 8 2.0

KCRV 0.0619 0.0012 1.9 Table 8. Measurement Results Reported by Individual NMIs/Laboratories for Cr in CCQM-K49


(mg/kg) Expanded

Uncertainty (mg/kg)


(%)

number of samples

k value

INMETRO (Brazil) NR

NIM (China) 0.0564 0.0035 6.2 6 2.0

PTB (Germany) 0.0479 0.0023 4.8 9 2.3

NMIJ (Japan) 0.0510 0.0019 3.7 5 2.0


IAEA (UN) NR*

NIST (USA, INAA) 0.0530 0.0036 6.8 6 2.0

KCRV 0.0514 0.0033 6.4 * Indicates that this NMI registered for this element but did not submit data

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Table 9. Measurement Results Reported by Individual NMIs/Laboratories for As in CCQM-K49


(mg/kg) Expanded

Uncertainty (mg/kg)


(%)

number of samples

k value

NMIA (Australia) NR*

NIM (China) 0.0168 0.0025 14.9 8 2.0


LGC (UK) 0.0202 0.0017 8.4 8 2.4

IAEA (UN) 0.0194 0.0010 5.2 5 2.0

NIST (USA, RNAA) 0.0196 0.0014 7.1 8 2.0

KCRV 0.01965 0.00131 6.7 * Indicates that this NMI registered for this element but did not submit data Table 10. Summary of Central Indicators for CCQM-K49

Element KCRV (mg/kg)

MM median Dispersion (mg/kg)

sMMshorth KCRU (mg/kg) U95 (location)

KCRU (%) U95 (location)

Fe 198.1 3.6 2.2 1.1 % Zn 181.9 3.1 1.9 1.0 % Se 2.056 0.062 0.077 3.7 % Cd 0.0976 0.0020 0.0016 1.6 % Pb 0.0619 0.0015 0.0012 1.9 % Cr 0.0514 0.0027 0.0033 6.4 % As 0.01965 0.00106 0.00131 6.7 %

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8. Discussion Results for this Key Comparison are highly encouraging in that all reported values, with only three exceptions, agreed within stated (expanded) uncertainties with the KCRVs, or were with an additional 1 % of the KCRV. Since this Key Comparison included 60 separate determinations of the studied constituents, 95 % of the results could be considered successful. It was originally anticipated that this study contained elements that were relatively easy to determine (Fe and Zn), moderately difficult to determine (Se, Cd and Pb), and very difficult to determine (Cr and As). As stated previously, the results of this comparison seem to bear this out, with the possible exception that Se was more difficult to determine than Cd and Pb, perhaps due to the difference in the amount of experience that many NMIs had with this element compared to Cd and Pb. However, Se seemed to be less difficult to determine than Cr and As based on the dispersion of the reported data and the typical expanded uncertainties reported by the NMIs. It is important to consider the applicability of this study to other elements and other matrices, or “how far does the light shine?” It seems relatively straightforward to project that successful participation in this study should extend to the same elements at similar levels in animal tissue samples, or animal-based food products. The only limitation might be for As in marine tissue samples where As is typically present in organically bound forms that can be resistant to some acid decomposition procedures. In addition, these organically-bound forms may react differently in some analytical instruments compared to inorganic As. Such behavior should be considered depending upon the methodology used to determine this element in a marine tissue sample, unless extremely rigorous digestion methods are used. A key issue for consideration is “what constitutes similar levels?” Since the material studied in this comparison was a dried tissue sample, concentrations about a third as great in wet tissue samples, and an order of magnitude lower in biological tissue samples would actually represent the same level, when dried. In addition, it would seem reasonable to consider that the light should shine to levels a factor of about three to five times lower, since it does not appear that any of the methods used were seriously impacted by their instrumental detection limits. Another key issue is how far can we extend the matrix from animal tissue samples. Many plant tissues contain organic constituents, such as phytates, that can bind some elements and may make these elements respond differently in some analytical instruments. In addition, many plant materials contain small amounts of sand or soil, which can contain significant fractions of some of elements. Most silicate fractions do not dissolve unless HF acid is used. Thus it seems reasonable to extrapolate the results from this study to plant tissues if rigorous digestion methods are used, or if no sample digestion is required. It also seems possible to extend the light further by considering the level of difficulty of the elements (and levels), and the difficulty of the matrix itself for the analytical methods used. As stated previously, it appears possible to generalize the difficulty of the elements studied to many, if not most, modern analytical methods. NMIs that were successful at all levels of difficulty for the elements studied might be expected to be similarly successful for other elements at comparable levels of difficulty in a matrix of similar (or lesser) difficulty. Of course this assumes that the NMI has had previous experience with these additional elements, since little can be said about capabilities of laboratories with limited experience for a particular measurand. In a similar manner, NMIs that were successful for elements of a

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moderate or easy level of difficulty in this comparison might be expected to be similarly successful for additional elements of equal difficulty in a matrix of similar difficulty. It is also important to consider the difficulty of the sample matrix for this comparison. Bovine liver, and animal tissues in general, are relatively easy to dissolve. Typically, open or microwave dissolution procedures successfully dissolve this material using nitric acid alone, and with the addition of hydrogen peroxide or perchloric acid, all constituents normally present can often be successfully mineralized. Added complexity can come from residual carbon remaining in the digest solution. The most notable effect being the enhancement of As and Se signals if measured by some non-nuclear methods. Moreover, the relatively high levels of a number of elements including Fe, Zn, Cu, Na, K, Mg, Ca, Cl, Br, P, S, etc. present challenges in terms of interferences and inter-element effects. Although the difficulty of the bovine liver matrix should be judged individually for each analytical method, as a general rule of thumb this matrix can be considered easy-to-moderately difficult for most modern, non-nuclear, methods of analysis, and moderately difficult-to-difficult for most nuclear based methods mainly due to the high levels of Na, Cl, Br and P. These elements produce elevated levels of background radiation (noise) under the peaks of interest for many other elements. The bovine liver matrix of this comparison does not appear to shine much light on “Amount of Substance Categories” 1-9; however, it should cover a significant portion of Category 10 (Biological fluids and materials) with the possible exception of 10.5 (Bone). The bovine liver matrix also is a direct fit for Category 11 (Food) with the exception of 11.3 (GMOs). In addition, if an NMI has aggressive digestion capabilities and experience, the light may shine to some matrices in Category 12 (Fuels), with the possible exception of 12.2 (Petroleum Products), Category 13 (Sediments, Soils, Ores and Particulates), with the possible exception of 13.3 (Ores), and Category 14 (Other), with the exceptions of 14.5 (Thin Films), 14.6 (Coatings), 14.9 (Adhesives) and possible exception of 14.8 (Rubber). 9. Equivalence Statements The degree of equivalence and its uncertainty between an NMI result and the KCRV is calculated according to the following equations: Di = (xi – xR) Ui

2 = (ki2 ui

2 + kR2 uR

2) where Di is the degree of equivalence between the NMI result xi and the KCRV xR, and Ui is the expanded uncertainty of Di calculated by both the combined standard uncertainty ui of xi and the standard uncertainty uR of xR. Equivalence statements in both absolute and relative values (to the KCRV) are given in Tables 11-17. 10. Summary Sixteen National Metrology Institutes (NMIs) submitted data for this Key Comparison using a variety of analytical methods. The Mixture Model Probability Density Function (MM-PDF) developed by David Duewar (applied using PDFMaker) was used to evaluate the data for each element in this study. The Mixture Model Median was selected as KCRV for each constituent and the U95%-location was selected as the KCRU.

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Results for this Key Comparison are highly encouraging in that all reported values, with only three exceptions, agreed within stated uncertainties with the Key Comparison Reference Values (KCRVs), or were within an additional 1 % of the KCRV. Since this Key Comparison included 60 separate determinations of the studied constituents, 95 % of the results could be considered successful. Measurands for this study consisted of elements that were expected to be relatively easy to determine (Fe and Zn), moderately difficult to determine (Se, Cd and Pb), and very difficult to determine (Cr and As). The results of this comparison seem to bear these rankings out, with the possible exception that Se was more difficult to determine than Cd and Pb, perhaps due to the difference in the amount of experience for many NMIs with this element compared to Cd and Pb. However, Se seemed to be less difficult to determine than Cr and As based on the dispersion of the reported data and the typical expanded uncertainties reported by the NMIs.

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Table 11. Equivalence Statements - Fe

NMI Reported

Value

(mg/kg)


(mg/kg)

Di (mg/kg)

Ui (mg/kg)

Di (%)

Ui (%)

INTI 209 14 10.9 14.2 5.5% 7.2% NMIA 198.1 8.2 0 8.5 0.0% 4.3% INMETRO 151.6 8.2 -46.5 8.5 -23.5% 4.3% NRC 207 9.1 8.9 9.4 4.5% 4.7% NIM 194.33 1.13 -3.77 2.5 -1.9% 1.2% LNE 196 3 -2.1 3.7 -1.1% 1.9% PTB 199.3 2.2 1.2 3.1 0.6% 1.6% HKGL 199.2 4.8 1.1 5.3 0.6% 2.7% INRIM 206.7 8.1 8.6 8.4 4.3% 4.2% NMIJ 199.1 3.3 1 4.0 0.5% 2.0% KRISS 197.78 0.68 -0.32 2.3 -0.2% 1.2% LGC 197.5 3.8 -0.6 4.4 -0.3% 2.2% IAEA 194 6 -4.1 6.4 -2.1% 3.2% NIST 197.1 2.3 -1 3.2 -0.5% 1.6% Table 12. Equivalence Statements - Zn

NMI Reported

Value

(mg/kg)


(mg/kg)

Di (mg/kg)

Ui (mg/kg)

Di (%)

Ui (%)

INTI 175 9 -6.9 9.2 -3.8% 5.1% NMIA 182.1 6.2 0.2 6.5 0.1% 3.6% INMETRO 181.1 4.8 -0.8 5.2 -0.4% 2.8% NRC 183 7.4 1.1 7.6 0.6% 4.2% NIM 177.6 1.21 -4.3 2.3 -2.4% 1.2% LNE 181 3 -0.9 3.6 -0.5% 2.0% BAM 184.4 1 2.5 2.1 1.4% 1.2% HKGL 181.7 4.9 -0.2 5.3 -0.1% 2.9% INRIM 187.8 7.9 5.9 8.1 3.2% 4.5% NMIJ 182.6 3.7 0.7 4.2 0.4% 2.3% KRISS 182.42 0.82 0.52 2.1 0.3% 1.1% LGC 182.0 4.2 0.1 4.6 0.1% 2.5% IAEA NR NIST 180.6 1.5 -1.3 2.4 -0.7% 1.3%

Page 18 of 34

Table 13. Equivalence Statements - Se

NMI Reported

Value

(mg/kg)


(mg/kg)

Di (mg/kg)

Ui (mg/kg)

Di (%)

Ui (%)

NMIA 2.07 0.11 0.014 0.134 0.7% 6.5% NIM 2.067 0.027 0.011 0.082 0.5% 4.0% INRIM 2.02 0.06 -0.036 0.098 -1.8% 4.7% KRISS NR

IAEA 2.17 0.06 0.114 0.098 5.5% 4.7% NIST (Combined) 1.993 0.035 -0.063 0.085 -3.1% 4.1% Table 14. Equivalence Statements - Cd

NMI Reported

Value

(mg/kg)


(mg/kg)

Di (mg/kg)

Ui (mg/kg)

Di (%)

Ui (%)

NMIA 0.1000 0.0062 0.0024 0.0064 2.5% 6.6% NIM 0.0975 0.0015 -0.0001 0.0022 -0.1% 2.2% LNE 0.093 0.0026 -0.0046 0.0031 -4.7% 3.1% BAM 0.0978 0.0006 0.0002 0.0017 0.2% 1.8% NMIJ 0.0963 0.0021 -0.0013 0.0026 -1.3% 2.7% KRISS NR

TUBITAK UME 0.110 0.0025 0.0124 0.0030 12.7% 3.0% IAEA 0.099 0.003 0.0014 0.0016 1.4% 1.7% NIST 0.0966 0.0013 -0.0010 0.0021 -1.0% 2.1%

Page 19 of 34

Table 15. Equivalence Statements - Pb

NMI Reported

Value

(mg/kg)


(mg/kg)

Di (mg/kg)

Ui (mg/kg)

Di (%)

Ui (%)

NMIA 0.0639 0.0037 0.0020 0.0039 3.2% 6.3% INMETRO 0.05046 0.00009 -0.0114 0.0012 -18.5% 1.9% NIM 0.0615 0.0042 -0.0004 0.0044 -0.6% 7.1% LNE 0.062 0.0014 0.0001 0.0018 0.2% 3.0% PTB 0.0624 0.0021 0.0005 0.0024 0.8% 3.9% KRISS 0.0613 0.0012 -0.0006 0.0017 -1.0% 2.7% TUBITAK UME 0.0616 0.0024 -0.0003 0.0027 -0.5% 4.3% IAEA 0.0586 0.003 -0.0033 0.0032 -5.3% 5.2% NIST 0.06282 0.00092 0.0009 0.0015 1.5% 2.4% Table 16. Equivalence Statements - Cr

NMI Reported

Value

(mg/kg)


(mg/kg)

Di (mg/kg)

Ui (mg/kg)

Di (%)

Ui (%)

INMETRO NR

NIM 0.0564 0.0035 0.0050 0.0048 9.7% 9.4% PTB 0.0479 0.0023 -0.0035 0.0040 -6.8% 7.8% NMIJ 0.0510 0.0019 -0.0004 0.0038 -0.8% 7.4% TUBITAK UME 0.0510 0.0017 -0.0004 0.0037 -0.8% 7.2% IAEA NR

NIST 0.0530 0.0036 0.0016 0.0049 3.1% 9.5%

Page 20 of 34

Table 17. Equivalence Statements - As

NMI Reported

Value

(mg/kg)


(mg/kg)

Di (mg/kg)

Ui (mg/kg)

Di (%)

Ui (%)

NMIA NR

NIM (China) 0.0168 0.0025 -0.00285 0.0028 -14.5% 14.4% TUBITAK UME 0.0205 0.0009 0.00085 0.0016 4.3% 8.1% LGC 0.0202 0.0017 0.00055 0.0021 2.8% 10.9% IAEA 0.0194 0.0010 -0.00025 0.0016 -1.3% 8.4% NIST (Combined) 0.0196 0.0014 -0.00005 0.0019 -0.3% 9.8%

Page 21 of 34

Figu

re 1

- Fe

in C

CQ

M-K

49

Page 22 of 34

Figu

re 2

- Zn

in C

CQ

M-K

49

Page 23 of 34

Figu

re 3

- Se

in C

CQ

M-K

49

Page 24 of 34

Figu

re 4

- C

d in

CC

QM

-K49

Page 25 of 34

Figu

re 5

- Pb

in C

CQ

M-K

49

Page 26 of 34

Figu

re 6

- C

r in

CC

QM

-K49

Page 27 of 34

Figu

re 7

- A

s in

CC

QM

-K49

Page 28 of 34

140

150

160

170

180

190

200

210

220

INM

ETRO

- B

razil

IAEA

(Seib

ers

dorf

)

NIM

- C

hin

a

LN

E -

Fra

nce

NIS

T -

USA

LG

C -

UK

KRIS

S -

Kore

a

NM

I -

Austr

alia

NM

IJ -

Japan

HKG

L -

Chin

a

PTB -

Germ

any

INRIM

- Ita

ly

NRC -

Canada

INTI -

Arg

enti

na

CCQM-K49 - Iron

Fe mass fractionKCRV+ U(95%)- U(95%)F

e m

ass

fra

cti

on (

mg/kg)

+ 1.1 %

- 1.1 %

Figure 8. Fe in CCQM-K49

Page 29 of 34

160

165

170

175

180

185

190

195

INTI -

Arg

enti

na

NIM

- C

hin

a

NIS

T -

USA

LN

E -

Fra

nce

INM

ETRO

- B

razil

HKG

L -

Chin

a

LG

C -

UK

NM

I -

Austr

alia

KRIS

S -

Kore

a

NM

IJ -

Japan

NRC -

Canada

BA

M -

Germ

any

INRIM

- Ita

ly

CCQM-K49 - Zinc

Zn mass fractionKCRV+ U(95%)- U(95%)

Zn m

ass

fra

cti

on (

mg/kg)

+ 1.0 %

- 1.0 %

Figure 9. Zn in CCQM-K49

Page 30 of 34

1.80

1.90

2.00

2.10

2.20

2.30

NIS

T -

IN

AA

INRIM

- Ita

ly

NIM

- C

hin

a

NM

I -

Austr

alia

IAEA

(Seib

ers

dorf

)

CCQM-K49 - Selenium

Se mass fractionKCRV+ U(95%)- U(95%)

Se m

ass

fra

cti

on (

mg/kg)

+ 3.7 %

- 3.7 %

Figure 10. Se in CCQM-K49

Page 31 of 34

0.07

0.08

0.09

0.10

0.11

0.12

LN

E -

Fra

nce

NM

IJ -

Japan

NIS

T -

USA

NIM

- C

hin

a

BA

M -

Germ

any

IAEA

(Seib

ers

dorf

)

NM

I -

Austr

alia

UM

E -

Turk

ey

CCQM-K49 - Cadmium

Cd mass fractionKCRV+ U(95%)- U(95%)C

d m

ass

fra

cti

on (

mg/kg)

+ 1.6 %

- 1.6 %

Figure 11. Cd in CCQM-K49

Page 32 of 34

0.045

0.050

0.055

0.060

0.065

0.070

INM

ETRO

- B

razil

IAEA

(Seib

ers

dorf

)

KRIS

S -

Kore

a

NIM

- C

hin

a

UM

E -

Turk

ey

LN

E -

Fra

nce

PTB -

Germ

any

NIS

T -

USA

NM

I -

Austr

alia

CCQM-K49 - Lead

Pb mass fractionKCRV+ U(95%)- U(95%)

Pb m

ass

fra

cti

on (

mg/kg)

+ 1.9 %

- 1.9 %

Figure 12. Pb in CCQM-K49

Page 33 of 34

0.035

0.040

0.045

0.050

0.055

0.060

PTB -

Germ

any

NM

IJ -

Japan

UM

E -

Turk

ey

NIS

T -

USA

NIM

- C

hin

a

CCQM-K49 - Chromium

Cr mass fractionKCRV+ U(95%)- U(95%)

Cr

mass

fra

cti

on (

mg/kg)

- 6.4 %

+ 6.4 %

Figure 13. Cr in CCQM-K49

Page 34 of 34

0.010

0.015

0.020

0.025

NIM

- C

hin

a

IAEA

(Seib

ers

dorf

)

NIS

T -

USA

LG

C -

UK

UM

E -

Turk

ey

CCQM-K49 - Arsenic

As mass fractionKCRV+ U(95%)- U(95%)A

s m

ass

fra

cti

on (

mg/kg)

+ 6.7 %

- 6.7 %

Figure 14. As in CCQM-K49

Documents

CCQM-K49 Key Comparison Essential and Toxic Elements in … · Thiago de Oliveira Araujo NRC Canada – Christine Scriver and Ralph Sturgeon NIM (China) – Jun Wang LNE (France)