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CCQM-K21: Key Comparison on the Determination of pp’-DDT in Fish Oil

Final Report March 2003

K S Webb, D Carter and C S J Wolff Briche

Laboratory of the Government Chemist, UK (Coordinating Laboratory) Introduction At the meeting of the CCQM held at Sèvres on 6 – 7 April 2000 it was decided to carry out a key comparison based on the determination of pp’-DDT in a fish oil matrix. This followed a successful pilot study on the determination of (pp’-dichlorodiphenyl) trichloroethane (pp’-DDT) in fish oil (CCQM-P21). The use of pp’-DDT has been banned in the majority of countries and the importation of goods containing pp’-DDT is, in some countries, subject to regulatory limits. As a member of the organochlorine class of pesticides it is very persistent with residues detectable many years after its use has ceased. Consequently its measurement is important, and pp’-DDT was selected for a pilot study and key comparison as an environmentally relevant trade related pesticide. An oil-based matrix was selected for the pilot study and key comparison since pp’-DDT accumulates preferentially in fat-type matrices and it is in such matrices that pp’-DDT measurements are usually made. For the pilot study CCQM-P21 participants used isotope dilution gas-chromatography-mass spectrometry (ID/GC/MS); consequently, participants were asked to use ID/GC/MS for this key comparison. The participants were: Australia, National Analytical Reference Laboratory (NARL) Canada, National Research Council of Canada (NRC) China, National Research Centre for Certified Reference Materials (NRCCRM) Germany, Bundesanstalt für Materialforschung und -prüfung (BAM) Japan, National Metrology Institute of Japan (NMIJ) Korea, Korea Research Institute of Standards and Science (KRISS) Russia, D. I. Mendeleyev Institute for Metrology of Gosstandart of Russia (VNIIM) United Kingdom, Laboratory of the Government Chemist (LGC) USA, National Institute of Standards and Technology (NIST) Pilot Study A pilot study (CCQM-P21) on the determination of pp’-DDT at two different levels in a fish oil matrix, with LGC as the coordinating laboratory, was held during 1999 - 2000. For CCQM-P21 participants were provided with two fish oil (dogfish liver oil) samples in duplicate. The fish oil contained a low natural level of pp’-DDT and an aliquot of this oil was also gravimetrically spiked with pp’-DDT. Thus two samples were sent to participants, one at the natural level (Sample A) and the other with a natural level plus

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fortification with pp’-DDT (Sample B). Participants were required to carry out measurements using their own calibration standards. However, in addition participants were provided with a pp’-DDT calibration standard solution so that they could make optional measurements based on the supplied standards. Participants were also provided with a pp’-DDT isotopic analogue (pp’-DDT-13C12) solution for spiking purposes. The nature of the fish oil matrix was such that that some form of clean-up procedure was required prior to analysis. Details of a suitable method based on gel permeation chromatography followed by use of a solid phase extraction (SPE) technique was made available to participants. Results were received from ten participants with all using ID/GC/MS, however, one participant used gas chromatography-electron capture detection for the measurement in the low level sample (Sample A). The mean mass fraction of pp’-DDT in the Sample A fish oil was 0.311 µg g-1 and for Sample B 4.669 µg g-1 (both with participants using their own calibration standards). At the lower level the results showed reasonable agreement (RSD 2.6%, own standard, RSD 1.6%, supplied standard). Agreement at the higher level was a little better (RSD 2.0%, own standard, RSD 1.2%, supplied standard). The gravimetric spiking of Sample B provided an opportunity to examine the correlation between participant’s measurements of Sample A and Sample B. This showed that the overall analytical data was confirmed by the gravimetric spiking to within 1%. Following discussion of the results amongst participants at the 2000 meeting of the CCQM Organic Working Group the CCQM directed the Organic Working Group to proceed to a key comparison. Key Comparison The key comparison involved sending two samples of fish oil to participants for measurement of the pp’-DDT levels. The fish oil material used for this key comparison was menhaden fish oil. Two aliquots of this oil were gravimetrically spiked with pp’-DDT. This enabled two samples to be sent to participants, Sample A (a low level of pp’-DDT) and Sample B (a level approximately 2.5 times higher than that of Sample A). Fortification was carried out by gravimetrically adding a solution of pp’-DDT in 2,2,4-trimethylpentane to the fish oil and mixing on a three dimensional rolling shaker for eight hours. No weight loss was observed following mixing which also resulted in the fish oil containing approximately 7% of 2,2,4-trimethylpentane by volume. A draft protocol was drawn up and circulated to prospective participants and to the Organic Working Group Chairman. Following the incorporation of comments the protocol was agreed and participation was finalised. Samples were circulated to the participants during October 2000. It was specified in the protocol that the samples could be safely stored at room temperature in the dark. Participants were responsible for the methods they used (but were requested to use ID/GC/MS at the measurement stage) and for providing their own calibration and isotopic analogue materials. It was suggested that, where appropriate, participants use the same method that they used for the pilot study on the determination of pp’-DDT in

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fish oil (CCQM-P21). Participants were supplied with duplicate vials of Samples A and B, each vial containing approximately 20 ml of sample. Participants were required to take two aliquots from each sample vial and analyse each aliquot in each of two instrumental runs (8 determinations in all for each sample). The samples contained 2,2,4-trimethyl pentane solvent. It was specified that care should be taken to avoid evaporative solvent loss during the sample handling stage and that the samples should be reported as received with no attempt made to correct for the presence of solvent in the samples. Participants were requested to report results on an absolute basis (corrected for chemical purity of their calibration standard material) together with the associated overall uncertainty. It was also necessary for participants to submit a full uncertainty budget. The mass fraction of pp'-DDT in the samples, in µg g-1, is given by:

b)spike(calisampleCM

le)spike(sampcalibcalibSMDDTpp MMR

MCMRC

××

×××=−′ (1)

where: RSM is the ratio of pp'-DDT/pp'-DDT-13C12 observed for the sample solution; RCM is the ratio of pp'-DDT/pp'-DDT-13C12 observed for the calibration

solution; Mcalib is the mass of the calibration solution taken for analysis; Ccalib is the mass fraction of pp’-DDT in the calibration solution in µg g-1; Mspike(sample) is the mass of the isotopically labelled spiking solution added to the

sample; Mspike(calib) is the mass of the isotopically labelled spiking solution added to the

calibration solution; Msample is the mass of the sample taken for analysis. The assumptions made here are (1) there is a negligible amount of the isotopically labelled analogue in the natural sample (2) pp’-DDT-13C12 is used as the isotopically labelled analogue and it is of high isotopic purity (it is readily available commercially with an isotopic purity better than 99%). Results Dates of study: April 2000 to March 2001. All of the participants submitted results; however, those of KRISS were at the low level (Sample A) only. Measurements were carried out during January 2001 for BAM, LGC, NIST and VNIIM, during February 2001 for NARL, NMIJ and NRC and during March 2001 for KRISS and NRCCRM.

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The results are shown in tabular form in Tables 1a and 1b for Samples A and B respectively and graphically in Figures 1 and 2 for Samples A and B respectively. The uncertainty bars in Figures 1 and 2 represent expanded uncertainties. Figures 1 and 2 also show the key comparison reference value (KCRV) together with the upper and lower limits of the 95 % confidence interval (C. I.) of the KCRV as described in Appendix 1. The Tables and Graphs of Equivalence are shown in Appendix 2 as Tables 3a and 3b and Figures 3 and 4 respectively. Uncertainty budgets for each of the participating NMIs are shown in Appendix 3 (Tables 4 to 13). Discussion The results of this key comparison show an improvement over those for the corresponding pilot study (CCQM-P21). The low level (Sample A) mean value of 0.0743 µg g-1 is much lower (by a factor of ~4) than that of the low level pilot study value of 0.311 µg g-1, however, the RSD values are not radically different (3.5% for this key comparison and 2.6% for the pilot study). The high level (Sample B) mean value of 0.1655 µg g-1 was lower than that of the low value of the pilot study (by a factor of ~2) and an RSD of 0.99% was achieved for this key comparison. For the fish oil material used for this study there was a small, unquantifiable, natural level of pp’-DDT. Fortification was carried out such that for the low level sample (Sample A) distributed to participants the mass fraction of pp’-DDT in the oil was increased by 0.0686 ± 0.0007 µg g-1 (expanded uncertainty) and for the higher level sample (Sample B) by 0.1613 ± 0.0017 µg g-1 (expanded uncertainty). Hence, allowing for the uncertainties detailed above results for the lower level sample (Sample A) should not be less than 0.0679 µg g-1 and results for the higher level sample (Sample B) should not be less than 0.1596 µg g-1. This is the case for both Sample A and Sample B results. Indeed, subtraction of the fortified levels from the means of the participants results shows a natural level in the samples of approximately 0.004 µg g-1 – 0.005 µg g-1 of pp’-DDT and evidence of correlation between the Sample A and Sample B results. It should be noted that in this key comparison no participant withdrew or changed their results. No requests for follow up bilaterals were received. In terms of uncertainty the calculations were reasonably consistent. The principal components of the uncertainty budget were set out in the protocol together with guidance on how to estimate them. These were between batch precision for the method as a whole (encompassing ratio measurements for samples and calibration standards) (Type A) and mass fraction of pp’-DDT in the calibration standard solution (corrected for purity) (Type B). Some participants experienced large variations in their replicate measurements and this is reflected in their uncertainties. Minor sources of uncertainty included balance linearity when carrying out weighing by difference. It was recognised that not all participants would carry out their measurements in the same manner or use the same type of calibration procedure consequently participants were asked to identify other

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uncertainty components applicable to their own procedure. For some participants additional uncertainty components were identified as being relevant to that particular institute. These include an uncertainty contribution for sample preparation (Tables 4a and 4b), for sample and standard isotope ratios (Table 5), instrument repeatability (Tables 6a and 6b) and a blank correction (Tables 7a and 7b). Additional data relating to sample clean-up, measurement and calibration procedures are detailed in Table 2. There does not appear to be a correlation of any of these parameters with uncertainty, in part due to the relatively low number of participants in this comparison. Conclusions This key comparison has demonstrated the ability of participating NMIs to measure pp’-DDT to a level of 0.07 µg g-1 in an oil based matrix to a high degree of accuracy. This is an improvement over the corresponding pilot study (CCQM-P21), particularly when considering that the high level value of 0.1655 µg g-1 is considerably lower than that of the low value of the pilot study (0.311 µg g-1) whilst an RSD to within 1% was achieved at that level. The compound pp’-DDT is a typical organochlorine pesticide and this key comparison has shown that NMIs have the ability to measure such compounds at levels typically found in the environment. The compound (pp’-dichlorodiphenyl) dichloroethylene (pp’-DDE), a metabolite of pp’-DDT, was the subject of a previous key comparison (CCQM-K5). The compound pp’-DDT is technically more challenging than that of pp’-DDE since it can decompose during the measurement procedure. Consequently the success of this key comparison, combined with that of CCQM-K5 demonstrates a broad measurement capability by NMIs for organochlorine compounds in the environment. Acknowledgements The participation of scientists from BAM (Germany), KRISS (Korea), LGC (United Kingdom), NMIJ (Japan), NIST (USA), NRC (Canada), NRCCRM (China), VNIIM (Russia) and NARL (Australia) is gratefully acknowledged.

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Table 1a. Results: Sample A Laboratory Mean Result

µg g-1 Std. Uncertainty

(u) µg g-1 Exp. Uncertainty

(U) µg g-1 BAM 0.0732 0.0007 0.0014 KRISS 0.0794 0.0007 0.0019 LGC 0.0756 0.0013 0.0027 NARL 0.0736 0.0009 0.0025 NMIJ 0.0711 0.0007 0.0013 NIST 0.0739 0.0004 0.0008 NRC 0.0725 0.0004 0.0008 NRCCRM 0.0724 0.0002 0.0004 VNIIM 0.0768 0.0004 0.0009 Overall mean of mean results = 0.0743 µg g-1 Std. Deviation of the mean = 0.00086 µg g-1. Degrees of freedom = 8 Coverage factor k = 2.306 Expanded uncertainty U = 0.0020 µg g-1 Table 1b. Results: Sample B Laboratory Mean Result

µg g-1 Std. Uncertainty

(u) µg g-1 Exp. Uncertainty

(U) µg g-1 BAM 0.1633 0.0015 0.0030 KRISS - - - LGC 0.1674 0.0025 0.0050 NARL 0.1644 0.0012 0.0030 NMIJ 0.1637 0.0025 0.0051 NIST 0.1673 0.0007 0.0017 NRC 0.1649 0.0009 0.0017 NRCCRM 0.1656 0.0003 0.0006 VNIIM 0.1670 0.0020 0.0050 Overall mean of mean results = 0.1655 µg g-1 Std. Deviation of the mean = 0.00058 µg g-1. Degrees of freedom = 7 Coverage factor k = 2.365 Expanded uncertainty U = 0.0014 µg g-1

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Table 2. Instrument types, calibration procedures and measurement parameters for pp’-DDT samples. Lab. Clean-Up Instrument Calibration

Method Quantitation

Ions Quantitation

Ions Ion Abundance Ion Abundance

Type pp’-DDT pp’-DDT-13C12 Ratio, Sample A Ratio, Sample B

BAM Alumina column Magnetic sector Bracketing 235 247 1.0 1.0

KRISS GPC + SPE Magnetic sector Bracketing 235 247 1.0

LGC GPC + SPE Magnetic sector Exact Matching 235 247 1.01 – 1.07 1.00 – 1.02

NARL GPC + SPE Magnetic sector (some Quadrupole)

Exact Matching 235 247 1.0 1.0

NMIJ GPC + SPE Magnetic sector Exact Matching 235 247 1.0 1.0

NIST GPC + SPE Quadrupole Bracketing Σ235 + 237 Σ247 + 249 1.01 1.01

NRC GPC + SPE Quadrupole Single Point Calib. Σ235 + 237 Σ247 + 249 1.47 – 1.70 1.34 – 1.96

NRCCRM GPC + Conc. H2SO4 Magnetic sector Bracketing 235 247 0.86 1.02

VNIIM Conc. H2SO4 Quadrupole Single Point Calib. 235 247 0.9 1.0 Note: GPC = Gel permeation chromatography SPE = Solid phase extraction HPLC = High performance liquid chromatography (preparative)

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Figure 1 Sample A Results showing Mean and Upper and Lower Limits of the 95% C. I. of the KCRV

0.068

0.070

0.072

0.074

0.076

0.078

0.080

0.082

Mea

sure

d ug

g-1

NIMC NRCCRM NRC NARLBAM NIST LGC VNIIM KRISS

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Figure 2 Sample B Results showing Mean and Upper and Lower Limits of the 95% C. I. of the KCRV

0.155

0.160

0.165

0.170

0.175

Mea

sure

d ug

g-1

BAM NIMC NARL NRCCRMNRC VNIIM NIST LGC

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Appendix 1 Key Comparison Reference Value (KCRV) It was proposed that the KCRV should be calculated as the mean of the results with the standard deviation of the mean taken as the standard uncertainty of the KCRV. This approach was agreed at a meeting of participants held at NIST (USA) in March 2001. The data contain a mix of degrees of freedom, consequently in order to calculate the coverage factor the Satterthwaite approximation is used, resulting in a coverage factor for Sample A of 2.306 (8 degrees of freedom) and a coverage factor for Sample B of 2.365 (7 degrees of freedom). For Sample A this calculation yields a KCRV of 0.0743 ± 0.0020 µg g-1 corresponding to a 95% confidence interval of 0.0723 µg g-1 to 0.0763 µg g-1. For Sample B the KCRV would be 0.1655 ± 0.0014 µg g-1 corresponding to a 95% confidence interval of 0.1641 µg g-1 to 0.1669 µg g-1. The Matrices and Graphs of Equivalence are shown in Appendix 2 as Tables 3a and 3b and Figures 3 and 4 respectively.

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Appendix 2 Table 3a Matrix of Equivalence for Sample A Measurand: Mass fraction of pp’-DDT in fish oil KCRV 0.0743 ± 0.0020 µg g-1

KCRV Di Ui

BAM -0.0011 0.00230 KRISS 0.0051 0.00241 LGC 0.0013 0.00319 NARL -0.0007 0.00277 NMIJ -0.0032 0.00226 NIST -0.0004 0.00206 NRC -0.0018 0.00209 NRCCRM -0.0019 0.00201 VNIIM 0.0025 0.00208

BAM KRISS LGC NARL NMIJ NIST NRC NRCCRM VNIIM Dij Uij Dij Uij Dij Uij Dij Uij Dij Uij Dij Uij Dij Uij Dij Uij Dij Uij

BAM -0.006 0.002 -0.002 0.003 0.000 0.003 0.002 0.002 -0.001 0.002 0.001 0.002 0.001 0.001 -0.004 0.002KRISS 0.006 0.002 0.004 0.003 0.006 0.003 0.008 0.002 0.006 0.002 0.007 0.002 0.007 0.002 0.003 0.002LGC 0.002 0.003 -0.004 0.003 0.002 0.003 0.005 0.003 0.002 0.003 0.003 0.003 0.003 0.003 -0.001 0.003NARL 0.000 0.003 -0.006 0.003 -0.002 0.003 0.003 0.003 0.000 0.002 0.001 0.003 0.001 0.003 -0.003 0.003NMIJ -0.002 0.002 -0.008 0.002 -0.005 0.003 -0.003 0.003 -0.003 0.001 -0.001 0.002 -0.001 0.001 -0.006 0.002NIST 0.001 0.002 -0.006 0.002 -0.002 0.003 0.000 0.002 0.003 0.001 0.001 0.001 0.001 0.001 -0.003 0.001NRC -0.001 0.002 -0.007 0.002 -0.003 0.003 -0.001 0.003 0.001 0.002 -0.001 0.001 0.000 0.001 -0.004 0.001NRCCRM -0.001 0.001 -0.007 0.002 -0.003 0.003 -0.001 0.003 0.001 0.001 -0.001 0.001 0.000 0.001 -0.004 0.001VNIIM 0.004 0.002 -0.003 0.002 0.001 0.003 0.003 0.003 0.006 0.002 0.003 0.001 0.004 0.001 0.004 0.001

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Table 3b Matrix of Equivalence for Sample B Measurand: Mass fraction of pp’-DDT in fish oil KCRV 0.1655 ± 0.0014 µg g-1

KCRV Di Ui

BAM -0.0022 0.0032 LGC 0.0019 0.0051 NARL -0.0011 0.0032 NMIJ -0.0018 0.0052 NIST 0.0018 0.0020 NRC -0.0006 0.0021 NRCCRM 0.0001 0.0014 VNIIM 0.0016 0.0046

BAM LGC NARL NMIJ NIST NRC NRCCRM VNIIM Dij Uij Dij Uij Dij Uij Dij Uij Dij Uij Dij Uij Dij Uij Dij Uij

BAM -0.004 0.006 -0.001 0.004 0.000 0.006 -0.004 0.003 -0.002 0.003 -0.002 0.003 -0.004 0.005LGC 0.004 0.006 0.003 0.006 0.004 0.007 0.000 0.005 0.003 0.005 0.002 0.005 0.000 0.006NARL 0.001 0.004 -0.003 0.006 0.001 0.006 -0.003 0.003 -0.001 0.003 -0.001 0.003 -0.003 0.005NMIJ 0.000 0.006 -0.004 0.007 -0.001 0.006 -0.004 0.005 -0.001 0.005 -0.002 0.005 -0.003 0.007NIST 0.004 0.003 0.000 0.005 0.003 0.003 0.004 0.005 0.002 0.002 0.002 0.002 0.000 0.005NRC 0.002 0.003 -0.003 0.005 0.001 0.003 0.001 0.005 -0.002 0.002 -0.001 0.002 -0.002 0.005NRCCRM 0.002 0.003 -0.002 0.005 0.001 0.003 0.002 0.005 -0.002 0.002 0.001 0.002 -0.001 0.005VNIIM 0.004 0.005 0.000 0.006 0.003 0.005 0.003 0.007 0.000 0.005 0.002 0.005 0.001 0.005

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Figure 3Degrees of Equivalence for Sample A

-0.0080

-0.0060

-0.0040

-0.0020

0.0000

0.0020

0.0040

0.0060

0.0080

BAM KRISS LGC NARL NMIJ NIST NRC NRCCRM VNIIM

Equi

vale

nce

(Di /

µg g

-1)

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Figure 4Degrees of Equivalence for Sample B

-0.0080

-0.0060

-0.0040

-0.0020

0.0000

0.0020

0.0040

0.0060

0.0080

BAM LGC NARL NMIJ NIST NRC NRCCRM VNIIM

Equi

vale

nce

(Di /

µg g

-1)

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Appendix 3 Uncertainty Budgets for Participating NMIs

Table 4a BAM – Sample A Parameter Uncertainty

Type Expanded

Uncertainty µg g-1 Degrees

of Freedom

Method precision A 0.000545 3 Calibration solution B 0.000215 Large Sample preparation B 0.000366 Large Standard uncertainty 0.0007 Coverage factor 2 Combined expanded uncertainty 0.014 Mean value of result 0.0732 Table 4b BAM – Sample B Parameter Uncertainty

Type Expanded


of Freedom

Method precision A 0.001144 3 Calibration solution B 0.0004792 Large Sample preparation B 0.0008165 Large Standard uncertainty 0.0015 Coverage factor 2 Combined expanded uncertainty 0.003 Mean value of result 0.1633

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Table 5 KRISS – Sample A Parameter Uncertainty

Type Standard


of Freedom

Method precision A 0.00065 2 Prep. of calibration mixture (1) precision

A 0.00002256 Large

Prep. of calibration mixture (2) precision

A 0.00002684 Large

Ratio calibration mixture (1) A 0.0000223 4 Ratio calibration mixture (2) A 0.00005316 4 Ratio sample A 0.000151 4 Balance precision B 0.00000268 Large Balance precision to include dilution

B 0.00003768 Large

Concentration standard solution B 0.00014985 Large Combined standard uncertainty 0.00068 Coverage factor 2.776 Combined expanded uncertainty 0.0019 Mean value of result 0.0794

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Table 6a LGC – Sample A Parameter Uncertainty

Type Relative

Uncertainty Degrees

of Freedom

Method precision A 0.0094 3 Instrument repeatability A 0.0128 4 Balance linearity, calibration solution

B 0.00004 Large

Calibration solution concentration

B 0.0067 Large

Balance linearity, sample spike B 0.00003 Large Balance linearity, calibration spike

B 0.00003 Large

Balance linearity, sample mass B 0.00004 Large Combined relative standard uncertainty 0.0172 Combined standard uncertainty 0.0013 µg g-1

Coverage factor 2 Combined expanded uncertainty 0.0027 µg g-1 Mean value of result 0.0756 µg g-1

Table 6b LGC – Sample B Parameter Uncertainty

Type Relative

Uncertainty Degrees

of Freedom

Method precision A 0.0056 3 Instrument repeatability A 0.0121 4 Balance linearity, calibration solution

B 0.00003 Large


B 0.0067 Large


B 0.00003 Large

Balance linearity, sample mass B 0.00003 Large Combined relative standard uncertainty 0.015 Combined standard uncertainty 0.0025 µg g-1

Coverage factor 2 Combined expanded uncertainty 0.005 µg g-1 Mean value of result 0.1674 µg g-1

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Table 7a NARL – Sample A Parameter Uncertainty

Type Relative

Uncertainty Degrees

of Freedom

Method precision A 0.01126 4 Balance linearity, calibration solution

B 0.00032 Large


B 0.00217 Large


B 0.00032 Large

Balance linearity, sample mass B 0.00032 Large Blank correction B 0.003 Large Combined relative standard uncertainty 0.01187 Combined standard uncertainty 0.0009

Coverage factor 2.78 Combined expanded uncertainty 0.0025 Mean value of result 0.0736

Table 7b NARL – Sample B Parameter Uncertainty

Type Relative

Uncertainty Degrees

of Freedom


B 0.00032 Large


B 0.00215 Large


B 0.00032 Large

Balance linearity, sample mass B 0.00032 Large Blank correction B 0.003 Large Combined relative standard uncertainty 0.00716 Combined standard uncertainty 0.0012


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Table 8a NMIJ – Sample A Parameter Uncertainty

Type Standard


of Freedom


B 0.0000048 Large


B 0.000025 Large


B 0.0000024 Large

Balance linearity, sample mass B 0.0000071 Large Combined standard uncertainty 0.00066

Coverage factor 2 Combined expanded uncertainty 0.0013 Mean value of result 0.0711

Table 8b NMIJ – Sample B Parameter Uncertainty

Type Standard


of Freedom


B 0.000011 Large


B 0.000058 Large


B 0.0000055 Large



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Table 9a NIST – Sample A Parameter Uncertainty

Type Standard


of Freedom

Measurement of samples A 0.000265 3 Measurement of calibration standards

A 0.000006 3

Concentration of calibration solution

B 0.000221 Infinity

Combined standard uncertainty 0.000346 Coverage factor 2.31 Combined expanded uncertainty 0.0008 Mean value of result 0.0739

Table 9b NIST – Sample B Parameter Uncertainty

Type Standard


of Freedom

Measurement of samples A 0.000550 3 Measurement of calibration standards

A 0.000013 3

Concentration of calibration solution

B 0.000501 Infinity

Combined standard uncertainty 0.000744 Coverage factor 2.23 Combined expanded uncertainty 0.0017 Mean value of result 0.1673

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Table 10a NRC – Sample A Parameter Uncertainty

Type Standard


of Freedom


B 0.00001359 Large


B 0.00005308 Large


B 0.00001410 Large



Table 10b NRC – Sample B Parameter Uncertainty

Type Standard


of Freedom


B 0.00003123 Large


B 0.0001158 Large


B 0.00003152 Large



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Table 11a NRCCRM – Sample A Parameter Uncertainty

Type Standard


of Freedom

Method precision A 0.00011 3 Balance linearity, calibration solution (higher weight ratio)

B 0.0000038 Large

Balance linearity, calibration solution (lower weight ratio)

B 0.0000031 Large


B 0.00011 Large

Balance linearity, sample spike B 0.00001 Large Balance linearity, calibration spike (higher weight ratio)

B 0.0000032 Large

Balance linearity, calibration spike (lower weight ratio)

B 0.0000021 Large



Table 11b NRCCRM – Sample B Parameter Uncertainty

Type Standard


of Freedom

Method precision A 0.00013 3 Balance linearity, calibration solution (higher weight ratio)

B 0.0000042 Large

Balance linearity, calibration solution (lower weight ratio)

B 0.0000096 Large


B 0.00026 Large

Balance linearity, sample spike B 0.000012 Large Balance linearity, calibration spike (higher weight ratio)

B 0.0000039 Large

Balance linearity, calibration spike (lower weight ratio)

B 0.0000081 Large



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Table 12a VNIIM – Sample A Parameter Uncertainty

Type Standard


of Freedom


B 0.00007 Large


B 0.00018 Large


B 0.00006 Large

Balance linearity, sample mass B 0.00002 Large Dilution B 0.00002 Large Combined standard uncertainty 0.0004


Table 12b VNIIM – Sample B Parameter Uncertainty

Type Standard


of Freedom


B 0.00212 Large


B 0.01051 Large


B 0.00232 Large

Balance linearity, sample mass B 0.00117 Large Dilution B Large Combined standard uncertainty 0.002


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