International Comparison CCQM-K41. Final Report. Page 1 of 55

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1 International Comparison CCQM-K41 Final Report Franklin R Guenther 1, Walter R Miller 1, David L. Duewer 1, Gwi Suk Heo 2, Yong-Doo Kim 2, Adriaan M.H. van der Veen 3, Leonid Konopelko 4, Yury Kustikov 4, Nina Shor 4, Chris Brookes 5, Martin Milton 5, Florbela Dias 6, Han Qiao 7 1 National Institute of Standards and Technology (NIST), Chemical Science and Technology Laboratory, 100 Bureau Drive Stop 8393, Gaithersburg, MD USA 2 Korea Research Institute of Standards and Science (KRISS), Division of Chemical Metrology and Materials Evaluation, P.O. Box 102, Yusong, Taejon, Republic of Korea 3 NMi Van Swinden Laboratorium B.V. (NMi VSL), Schoemakerstraat 97, 2628 VK Delft, the Netherlands 4 D.I.Mendeleyev Institute for Metrology (VNIIM), Research Department fot the State Measurement Standards in the Field of Physico-Chemical Measurements, 19, Moskovsky Prospekt, St-Petersburg, Russia 5 National Physical Laboratory (NPL), Teddington. Middlesex, TW11 OLW, UK 6 Instituto Português da Qualidade, IPQ, Monte da Caparica, Portugal 7 National Research Center for Certified Reference Materials (NRCCRM), No. 7, District 11, Heping Street, Beijing, P.R. Chine Field Amount of Substance: Gas Standards Subject Comparison of gas standards containing 10 μmol/mol hydrogen sulfide in a balance of nitrogen. Participants Table 1: list of participants in this key comparison. Acronym Country Institute KRISS KR Korea Research Institute of Standards and Science (KRISS), Division of Chemical Metrology and Materials Evaluation, P.O. Box 102, Yusong, Taejon, Republic of Korea IPQ PT Instituto Português da Qualidade, IPQ, Monte da Caparica, Portugal NIST US National Institute of Standards and Technology (NIST), Chemical Science and Technology Laboratory, 100 Bureau Drive Stop 8393, Gaithersburg, MD USA NMi-VSL NL NMi Van Swinden Laboratorium B.V., Delft, the Netherlands NPL UK National Physical Laboratory (NPL), Teddington. Middlesex, TW11 OLW, UK NRCCRM CN National Research Center for Reference Materials, Beijing, P.R. China VNIIM RU D.I.Mendeleyev Institute for Metrology (VNIIM), Research Department for the State Measurement Standards in the Field of Physico-Chemical Measurements, 19, Moskovsky Prospekt, St-Petersburg, Russia Page 1 of 55

2 Organizing body: CCQM Gas Analysis Working Group Background This key comparison was intended to compare the capabilities for the preparation and value assignment of gas standards for hydrogen sulfide in nitrogen (subsequently referred to as H 2 S), maintained at the participating national metrology institutes. The range of the nominal amount-ofsubstance fractions of the comparison standard is 10 μmol/mol, which is close to regulatory levels in most countries. Conduct of the Comparison The National Institute of Standards and Technology (NIST) procured ten 6-liter gas mixtures of 10 μmol/mol H 2 S in nitrogen from Scott Marin Gases, Riverside CA, USA. These gas standards were monitored for 6 months prior to the start of the key comparison exercise in order to assure stability. Each standard was analyzed and referenced to a nominal 10 μmol/mol NIST stable reference cylinder (SRC), which had been observed to be stable of many years. Prior to the start of the comparison, seven of the ten standards were selected for distribution to the participants based on stability over the 6-month evaluation period. A comparison to the NIST stable reference cylinder was performed prior to shipment of the cylinders to the participants. Each participating laboratory was shipped one 6-liter cylinder. This cylinder was to be analyzed by the receiving laboratory and then returned to NIST. NIST then reanalyzed the cylinder contents, again referenced to the SRC, to assure that the compounds remained stable throughout the comparison. The comparison was officially declared closed on April 1, All participating laboratories had submitted complete reports by this date. The report from NRCCRM had originally been reported as not received; however review of records show that the report was indeed received prior to April 1, As there is no gravimetric value for these comparison cylinders, a consensus reference value is calculated from the results received from the participants. NIST comparisons to the stable reference cylinder are used to normalize the participants data to remove cylinder to cylinder concentration differences. In effect the Key Comparison reference value is the calculated concentration of the SRC. NIST Instrumentation Non-dispersive Ultra-Violet Spectrometer (NDUV): This instrument (Western Research Series 900 Analyzer, model 922) was operated on the 0 25 mol/mol setting with a span concentration of mol/mol. The internal pump was adjusted to deliver a constant flow of 500 ml/min. An automated stream selection device was used to randomly select the flow from one of five cylinders. The regulator on each cylinder was adjusted to give a flow of approximately 600 ml/min. This flow was swept past the inlet of the instrument, where 500 ml/min was directed into the instrument port and 100 ml/min exhausted to vent. The sample line was purged for a minimum of 3 minutes. The analog signal (10 V output) from the instrument was averaged over two minutes for each reading. Figure 1 shows the reproducibility achieved using this instrument. A series of measurements of the SRC was done over a time period of one day. Figure 1 shows the response from 90 measurements from the NDUV. From this data it was determined that the combined uncertainty Page 2 of 55

3 (k=1) of the ratio was 0.25 % relative. The uncertainty bars for 0.25 % relative are shown in Figure 1 with red lines. This uncertainty was applied to all ratios obtained using this instrument. Figure 1: NDUV Reproducability Signal (V) Run Electrochemical analyzer: This instrument (Interscan, model RM-17) was operated on the 0 50 mol/mol range with the span potentiometer set to This was done to adjust the instrument sensitivity such that the 10 mol/mol samples gave a response at 60 % of range. The internal sample pump was adjusted to deliver a constant flow rate of 100 ml/min. An automated stream selection device was used to randomly select the flow from one of five cylinders. The regulator on each cylinder was adjusted to give a flow of approximately 200 ml/min. This flow was swept past the inlet of the instrument, where 100 ml/min was directed into the instrument port and 100 ml/min exhausted to vent. The sample line was purged a minimum of 3 minutes. The analog output (10 mv) was averaged over two minutes for each reading. To measure the reproducibility of the Interscan, a series of measurements of the SRC was completed, and is show in Figure 2. This instrument does exhibit short term drift that requires correction. The sampling protocol used by NIST removes this short term drift by use of a control sample. For this project the control was the SRC. Figure 3 shows the method used to correct for this drift. In this figure five of the comparison cylinders are shown along with the SRC (labeled Control). As can be seen significant drift is being exhibited by the Interscan instrument. However, when the ratio of the sampled cylinder to the control is calculated, the drift is minimized and very good reproducibility is achieved (Table 2). A conservative estimate of 0.25 % relative was used for all ratios measured using the Interscan instrument. Figure 2: Interscan Reproducibility Response (mv) Run Page 3 of 55

4 Figure 3: Interscan Reproducibility data Response (mv) Control WS-10A FA02278 FA02282 FA02277 FF Run Table 2: Interscan Reproducibility Data Ratio Ratio Ratio Std Sample / Sample / Sample / Average Dev % RSD Sample WS-10 WS-10 WS-10 FA % FA % FA % FF % WS-10A % To test the linearity of the Interscan, a permeation system was adjusted to give concentration between 8 and 12 mol/mol hydrogen sulfide in nitrogen. In figure 4, the data shows that the Interscan is linear in this concentration range. Figure 4: Interscan Linearity y = x R 2 = Response Ratio Concentration ( μ mol/mol) NIST Stability Measurements NIST used a non-dispersive ultra-violet spectrometer (NDUV) and an electrochemical analyzer (Interscan) to measure the hydrogen sulfide in each cylinder. The response from the sampled Page 4 of 55

5 cylinder (r S ) and the response from the SRC (r R ) were measured and the response ratio calculated according to the following formula: r S r i = (1) rr This was done in order to remove any short term drift the instrument may exhibit and to reference each cylinder to the SRC. A sampling sequence of SRC, sample, SRC was used. The two measurements of the SRC were averaged to calculate r R. The response ratio was measured periodically prior to shipment of the cylinders to the participant in order to monitor stability. The response ratio was again measured once the cylinder was returned from the participants. Graphs of the response ratios over the duration of this study for each cylinder are shown in Appendix A, graphs 1 through 8. The calculated average of the ratios determined by NIST is shown in the graphs along with the expanded uncertainty (k=2). The position of the average along the x-axis is the actual date the participant analyzed the cylinder, as reported by the participant. The identification of the cylinder each NMI received and analyzed along with the average response ratio ( r i ) and associated expanded uncertainty (k=2) measured by NIST is given in Table 3. For each cylinder the average ratio was used in the calculation of the Key Comparison Reference value. No stability effects could be positively determined, as all ratios were within their uncertainty bars. Some minor stability issues may be apparent in the cylinders that traveled to IPQ and NRCCRM. However in all cases the average ratio compensates for any stability issues. An extra cylinder in the study was sent to NMi and returned without analysis at NMi. This cylinder was then reanalyzed at NIST to determine if any effects from travel could be detected. No travel effects were detected. Table 3: Study Cylinders Institute Cylinder Number Average Ratio to SRC ( r i ) KRISS FA ± IPQ FA ± NIST FF ± NMi-VSL FA ± NPL FA ± NRCCRM FF ± VNIIM FA ± Travel Cylinder FF ± Results All participating laboratories sent in their complete report prior to the April 1, 2005 deadline except VNIIM, which sent only their results table on April 1. A full report from VNIIM was subsequently received on May 13, Since the results table was received before the deadline, the full report has been accepted. The report from KRISS was received on March 30, 2005, however a subsequent report was received on April 1, 2005 with corrected values. Since this report with corrected values was received before the deadline, it has been accepted as the final report from KRISS. All final reports from the participants are attached as received in Appendix B. A summary of the reported results is given in Table 4, along with the NIST determined average response ratio to the SRC. The instruments and methods used by the participants are summarized in Table 5. Since all the cylinders contained a different concentration of hydrogen sulfide, and a gravimetric value was not available, a consensus value was determined for the Key Comparison Reference value (KCRV). To calculate the KCRV, the reported value from each participant was divided by Page 5 of 55

6 the NIST determined average response ratio. This calculation gives the concentration of the SRC, as would be determined by the participant. The equation used was: X = i SRC X r i i, (2) X i is the concentration reported by the participant, ri is the average response ratio for where cylinder the participant analyzed, and X i, SRC is the calculated concentration of the SRC. The uncertainty of this concentration u ) was calculated using: ( X i,src ( X i, SRC ) = X i, SRC u( X i) X i 2 u( ri ) + ri u (3) where ( X i ) the average response ratio measured by NIST. u is the participants reported uncertainty divided by k, and r ) 2 u is the uncertainty of Table 4 summarizes the results obtained from the NIST stability analyses and the reported values from the participants. The final two columns in the table lists the calculated value for the stable reference cylinder (SRC) using the participants and NIST data. This data is also graphically represented in Figure 5, with the reported values on the left in red and the calculated values for the SRC on the right. Table 4: Summary of values Cylinder NMI X i Reported Concentration ( mol/mol) U ( X i ) NIST Ratio Determination r i U r ) ( i ( i Calculated SRC Value ( mol/mol) X i, SRC U (,SRC ) (k=2) (k=2) (k=2) FA02288 KRISS FA02267 IPQ FF21074 NIST FA02295 NMi-VSL FA02283 NPL FF17172 NRCCRM FA02270 VNIIM X i Page 6 of 55

7 Table 5: Instruments and methods NMI Instrument Standards/Calibration Repeat Measurements 2 gravimetrically prepared primary gas Agilent 6890 GC-G sets of measurements, each standards, single point calibration. KRISS Atomic Emission Detector, consisting of 6 subsets each with 8 Standard within 0.05 μmol/mol of CP-SIL 5CB 25m column measures of PSM and sample sample IPQ NIST LIMAS11 NDUV Model RM17 electrochemical voltammetric sensor (Interscan) 3 primary gas standards prepared by NMi-VSL (25, 50, 150 mol/mol) and one primary gas standard prepared by IPQ (9.43 μmol/mol) 20 cm permeation tube, contained within thermostatically controlled environment. Manual weightings using Mettler AT261. Flow calibration using Molblocs. 3 sets of measurements, each consisting of an unknown number averaged results. 3 measurement periods, each consisting of 5 repeat cycles between 4 permeation generated concentrations, the sample, and two controls. NMi-VSL Model RM17 electrochemical voltammetric sensor (Interscan) Gravimetric primary standards at 10, 20, 40, 60, 80, and 100 μmol/mol. Quadratic fit using ISO sets of measurements, each consisting of average of 90 measurements of each cylinder. NPL Varian GC with Sulfur Chemiluminescence Detection, RH-1 60m column. Two methods of sequencing samples. 4 gravimetrically prepared primary standards in BOC Spectraseal and Scott Acculife cylinders (9.7 to mol/mol) Multiple replicates of single point calibrations against three primary standards. Each measurement run consisted of injections at 15 s intervals NRCCRM Agilent 4890 GC with flame photometric detection, GS- GASPRO 60m column 6 gravimetrically prepared primary gas standards. All standard between 9.45 and 9.58 mol/mol 3 sets of measurements, each consisting of 6 concentration determinations. VNIIM Crystal GC unknown detector, DB-1 60m column 2 sets of 3 permeation tubes certified using thermo-gravimetric instrument. Unknown flow calibration with nitrogen dilution. 7 independent measurements, each consisting of 5 sub-measurements of sample to permeation system. Calculation of Key Comparison Reference Value Figure 5a displays the values and their 95% uncertainty intervals for both the reported and SRCadjusted concentrations. The empirical probability density function (PDF) for the SRC-adjusted values, calculated assuming that the X i,src and the U 95 ( X i,src ) specify N(X i,src, U 95 ( X i,src )/2) normal kernel densities, is displayed at the right edge of the Figure. The solid horizontal line represents the median of the PDF (half of the PDF area is above the line, half is below). The dashed horizontal lines enclose 95% of the area of the PDF (2.5% of the area is above the upper dashed line, 2.5% of the area is below the lower dashed line). The remarkable overlap of six of the seven results and the relatively large uncertainty on the less-concordant NCCRM result strongly suggests that the consensus location for these data is about within the region 9.96 mol/mol to mol/mol. However, these data raise more general questions regarding the philosophical basis for assigning the consensus Key Comparison Reference Value (KCRV) and its associated 95% confidence interval, U 95 (KCRV), that could be significant for future comparisons. A number of scenarios need to be considered: 1) Ignore the U 95 ( X i,src ), treat as a Normal distribution.. The unambiguously most efficient estimates for the location and dispersion of a putatively representative, normally distributed set of data are the mean and the standard deviation. Under this assumption, the KCRV = mol/mol and U 95 (KCRV) = (t 0.05,5 )(0.187)/ 7 = (2.57)(0.187)/2.65 = mol/mol. 2) Ignore the U 95 ( X i,src ), identify and exclude statistical outlier X i,src. By inspection, the X NCCRM,SRC is not in the same population as the other six. Excluding this value, the mean and the standard deviation of the remaining six values give a KCRV = mol/mol and U 95 (KCRV) = (2.57)(0.029)/2.45 = mol/mol. Page 7 of 55

8 3) Ignore the U 95 (X i,src ), estimate the Normal component of a mixture distribution. There are many different robust estimates for the location and dispersion of a set of values that contain a modest percentage of discordant values. 1 Three of the simplest are: a. The median and the median absolute deviation from the median (MAD), adjusted to estimate the standard deviation when the distribution is truly normal (MADe). 2,3 These estimators give KCRV = mol/mol and U 95 (KCRV) = (2.57)(0.038)/ 7 = mol/mol. b. Huber s Estimate Number 2, H15 and S15. 3 These estimators give KCRV = mol/mol and U 95 (KCRV) = (2.57)(0.042)/ 7 = mol/mol. c. The Least Power 1.5, L1 and sl1. 4 These estimators give KCRV = mol/mol and U 95 (KCRV) = (2.57)(0.074)/ 7 = mol/mol. There is no agreement on which of these (or other) robust estimators is best for any given set of data. Here, it appears that Huber s method gives slightly more influence to X NCCRM,SRC than the median and the MADe but somewhat less than does the Least Power ) Use the U 95 (X i,src ) as weighting functions, exclude statistical outliers. There are many different weighted mean estimates for the location and dispersion, all based on the assumption that there exists a functional relationship between the estimated measurement uncertainty and the bias between the reported and the true value. 1 These methods typically estimate the variability of the location estimate, not of the population of values (and there is little agreement on how best to estimate this variability). 5 The simplest method gives influence to values as the inverse-square of the uncertainties, giving for the six concordant values a KCRV = mol/mol and a U 95 (KCRV) = (2.57)(0.012) = mol/mol. The Mandel-Paule method limits the influence of under-estimated uncertainties; for these data, it gives KCRV = mol/mol and a U 95 (KCRV) = (2.57)(0.012) = mol/mol. 5) Use the U 95 (X i,src ) as weighting functions, do not exclude statistical outliers. The weighted mean estimates are not robust to outliers; however, with this data, the U 95 (X NCCRM,SRC ) is large and so will not be given much influence. Using all seven values, both the inverse-square and Mandel-Paule methods give a KCRV = mol/mol and a U 95 (KCRV) = (2.57)(0.017) = mol/mol. However, it should be realized that should the U 95 (X NCCRM,SRC ) be increasingly under-estimated, the value of the KCRV would be increasingly pulled towards the X NCCRM,SRC value = mol/mol and the U 95 (KCRV) towards (and beyond) the (uniformly-weighted) standard deviation, mol/mol. 6) Use the U 95 (X i,src ) as kernel densities, estimate the Normal component of a mixture distribution.. Assuming that the measurements can be validly represented as N(U 95 (X i,src ),U 95 (X i,src )/2) normal kernels, location and dispersion estimates can be 1 D.L. Duewer. A Robust Approach for the Determination of CCQM Key Comparison Reference Values and Uncertainties. Working document CCQM/04-15, BIPM, Analytical Methods Committee of the Royal Society of Chemistry, Technical Brief 6 (April 2001), Robust statistics: a method of coping with outliers, 3 S. Ellison, Robust Statistics Toolkit (RobStat.xla) Excel add-in, 4 F. Pennecchi and L. Callegaro. Between the mean and the median: the Lp estimator. Metrologia 2006;43: N.F. Zhang, The uncertainty associated with the weighted mean of measurement data. Metrologia 2006;43: Page 8 of 55

9 defined that are simultaneously robust to discordant X i,src and under-estimated U 95 (X i,src ). 1 The PDF-median, shown in Figure 5a, is itself a location estimate, giving a KCRV of mol/mol. While the empirical 95% confidence interval for the PDF provides a direct estimate of the dispersion of the population, 6 a more robust estimate is provided by the PDF-interquartile range (spdf-iqr), the interval spanning the central 50% of the PDF area, adjusted to estimate the standard deviation when the distribution is truly normal. 7 The spdf-iqr for these data is mol/mol, giving U 95 (KCRV) = (2.57)(0.072)/2.65 = mol/mol. However, the PDF-based dispersion estimates include both the variability among the X i,src and the U 95 (X i,src ). The U 95 (KCRV) estimates provided in the scenarios above only estimate the variability among the X i,src. To make the two types of estimate concordant, either the non-pdf dispersion estimates need to be expanded to include the U 95 (X i,src ) contribution or the PDF estimates need to be reduced. Given that the median U 95 (X i,src ) for these data is mol/mol (that is, larger than the spdf-iqr), it is clear that the U 95 (X i,src ) dominate the total uncertainty and reduction of the PDF-based estimates does not provide useful estimates of just the among-x i,src. The appropriate comparison would then be to the among-x i,src estimates of dispersion augmented with 2 2 the median U 95 (X i,src ): s + u ( X ) s total among i, SRC =. Note that all U 95 (KCRV) calculated from such augmented values will be somewhat larger than that calculated from the spdf- IQR. As a general principle, it is inappropriate to exclude particular data from a consensus estimate unless there is a defensible technical reason for doubting that it is in fact a valid member of the majority distribution of the data. However, it is also generally inappropriate to bias consensus estimate towards extreme values. While weighted estimates are defensible for these particular data since the least-concordant X i,src has an appropriately large U 95 (X i,src ), it seems preferable to use methods expected to perform adequately under more general conditions. Also, given that it is desired to use the information contained in the U 95 (X i,src ) estimates, is seems appropriate to include them in the dispersion calculation. The PDF-median and spdf-iqr fully utilize the dispersion and location information provided in reported U 95 (X i,src ) and are robust to extreme X i,src and to both over- and under-estimated U 95 (X i,src ). The recommended consensus KCRV for the SRC results is therefore the PDFmedian, mol/mol hydrogen sulfide in nitrogen. The recommended consensus U 95 (KCRV) is based upon the spdf-iqr, mol/mol hydrogen sulfide in nitrogen. This value is used in Table 6 to determine the degrees of equivalence. In Figure 5b the KCRV is plotted (black line) along with the 95% confidence interval for the KCRV (red lines) and the 95% confidence interval for the population (blue lines). The participants reported values are plotted on the left of the figure, and the calculated values for the SRC on the right. Degree of Equivalence The degree of equivalence for each participating laboratory was calculated with the equation: D i = X, z (6) i SRC c The uncertainty of the degree of equivalence was calculated using the equation: 6 P. Ciarlini, M.G. Cox, F. Pavese. G. Regoliosi. The use of a mixture of probability distributions in temperature interlaboratory comparisons. Metrologia, 2004, 41, Stuart, A., Ord, J.K. Kendall s Advanced Theory of Statistics. Volume 1. Distribution Theory. Sixth Edition, Chapter 10. Edward Arnold, London, Page 9 of 55

10 U ( Di ) 2 u( X i, SRC ) u( zc ) = (7) The degree of equivalence and uncertainty is summarized in Table 6, and graphically represented in Figure 6. The KCRV lies within the uncertainty bounds of all the participants value for the SRC. For all participants, except for NRCCRM, the agreement is excellent for this reactive compound, and demonstrates excellent comparability. While the value and uncertainty from NRCCRM does show that the KCRV falls within the extremes of the uncertainty bounds, the result shows evidence of a bias of approximately 0.5%. Table 6: Degree of Equivalence Calculated SRC Value KCRV Degree of Equivalence Cylinder NMI Value uncertainty Value uncertainty D U(D) FA02270 VNIIM FA02283 NPL FA02295 NMi FA02267 IPQ FA02288 KRISS FF21074 NIST FF17172 NCCRM Figure 5a: Graph of PDF median and 95% interval mol/mol (VNIIM) (NPL) (NMI/VSL) (IPQ) (KRISS:) (NIST) Reported Concentration (NRCCRM) VNIIM NPL NMI/VSL IPQ KRISS NIST NRCCRM SRC-Adjusted Concentration Page 10 of 55

11 Figure 5b: Graph of Results CCQM-K41: Hydrogen Sulfide 10 mol/mol nominal (VNIIM ) (NPL ) (NMi-VSL ) (IPQ ) (KRISS ) (NIST ) (NRCCRM ) Values as Reported VNIIM NPL NMi-VSL IPQ KRISS NIST NRCCRM KCRV Calculated Values Figure 6: Degrees of Equivalence 1.20 CCQM-K41: Degree of Equivalence (10 μmol/mol Hydrogen Sulfide) 1.00 Degree of Equivalence ( μ mol/mol) VNIIM NPL NMi IPQ KRISS NIST NCCRM Laboratory Page 11 of 55

12 Limits of Claims This Key comparison may be used to assess calibration and measurement capability (CMC claims for hydrogen sulfide in nitrogen or air, at a concentration between 1 mol/mol and 500 mol/mol. This Key comparison may also be used as evidence for CMCs of hydrogen sulfide in methane at the above concentrations, as long as the analytical method and instrumentation are similar to that used for nitrogen balance hydrogen sulfide gas mixtures. Coordinator Franklin R. Guenther National Institute of Standards and Technology (NIST) Gaithersburg, Maryland USA Project Reference: CCQM-K41 Completion Date: April 2005 Participant Contact List Florbela Dias Instituto Português da Qualidade (IPQ) Monte da Caparica Portugal Han Qiao National Research Center for Certified Reference Materials (NRCCRM) No. 7, District 11 Heping Street, Beijing, P.R. Chine Dr. Jin Seok Kim Korea Research Institute of Standards and Science (KRISS) Division of Chemistry and Radiation P.O. Box 102 Yusung Taejon, Korea Adriaan M.H. van der Veen Nederlands Meetinstituut (NMi) Schoemakerstraat 97 Postbus AR DELFT The Netherlands Dr. Leonid Konopelko D.I. Mendeleyev Institute for Metrology (VNIIM) 19, Moskovsky Prospekt St. Petersburg Russia Page 12 of 55

13 Dr. Martin J.T. Milton National Physical Laboratory (NPL) Environmental Standards Section Teddington Middlesex TW11 0LW England Dr. Franklin R. Guenther National Institute of Standards and Technology (NIST) Chemical Science and Technology Laboratory 100 Bureau Drive Gaithersburg, MD USA Page 13 of 55

14 Appendix A FA02288 (KRISS) Ratio April-04 August-04 November-04 February-05 May-05 September-05 Date Stability Data Average FA02267 (IPQ) Ratio April-04 August-04 November-04 February-05 May-05 September-05 Date Stability Data Average Page 14 of 55

15 FF21074 (NIST) Ratio April-04 August-04 November-04 February-05 May-05 September-05 Date Stability Data Average FA02295 (NMi-VSL) Ratio April-04 August-04 November-04 February-05 May-05 September-05 Date Stability Data Average Page 15 of 55

16 FA02283 (NPL) Ratio April-04 August-04 November-04 February-05 May-05 September-05 Date Stability Data Average FF17172 (NRCCRM) Ratio April-04 August-04 November-04 February-05 May-05 September-05 Date Stability Data Average Page 16 of 55

17 FA02270 (VNIIM) Ratio April-04 August-04 November-04 February-05 May-05 September-05 Date Stability Data Average FA02282 (Travel) Ratio April-04 August-04 November-04 February-05 May-05 September-05 Date Stability Data Average Page 17 of 55

18 Appendix B Participant: KRISS Confirmation form for the received cylinder Laboratory : KRISS Name of the contact person : Gwi Suk Heo address : heo@kriss.re.kr Date of reception : December, 2004 Cylinder number : FAO2288 Initial inner pressure of Cylinder as received * : 1100 PSIG Other remarks on the conditions of the cylinder (paint, packaging, and other any damages to the cylinder) : NO NOTICIABLE DAMAGE. IT COMES GOOD CONDITION. * Information on an inner pressure is important to confirm that no sample loss occurred in the course of transport. Page 18 of 55

19 Measurement report: Hydrogen sulfide in nitrogen Laboratory Cylinder number : KRISS : FAO2288 NOMINAL COMPOSITION : mol/mol Measurement Date Result (umol/mol) stand. uncertainty (% relative) number of submeasurements No x 4 No x 2 No x 3 No x 3 No x 4 Note: Please copy this table as many times as needed for reporting additional measurements Result: with purity correction of H2S (99.6 ± 0.3%) Gas mixture Result (assigned value) Coverage factor Assigned expanded uncertainty (*) Hydrogen sulfide umol/mol umol/mol Reference Method: Describe your instrument(s) (principles, make, type, configuration, data collection etc.): HP6890 GC-G2350 AED (Agilent, USA) were used for analysis. Gas switching valve at 100 o C temp was used with 1 ml sample loop. Sample gas was continuously passed through sampling loop during the analysis. Sample flow-rate was controlled using MFC located at front of sampling valve. CP-SIL 5CB(Varian) GC column was used(25 m x 0.53 mm id x 5 um thickness with dimethylsilicon). GC oven temperatue was set at isothermal condition of 35 o C (4 min). Column flow was 5 ml/min and EPC used for constant column flow. High purity Helium was used as carrier gas. Sample gas was split 5:1 at VI inlet before transferring to GC column. AED transferline temp was set 250 o C and cavity temp was 250 o C. High purity Helium was used as AED discharge gas, which was supplied with EPC control. AED cavity pressure was maintained at 1.5 psi. High purity hydrogen used for ADE with EPC controlled pressure at 8.6 psi. High purity oxygen was used for AED with EPC controlled pressure at 17.5 psi. AED signal was acquired by Agilent Chemstation and GC-AED data was processed using Chemstation software. Sulfur emission line of 181 nm was monitored for sulfur analysis by AED. Calibration Standards: Describe your Calibration Standards for the measurements (preparation method, purity analyses, estimated uncertainty etc.): Page 19 of 55

20 Purity of hydrogen sulfide (from Aldrich) was checked by several measurement techniques. Gas MS was used for impurity analysis of moisture (4390 ppm), helium (<1 ppm)and argon(23 ppm), GC-MS was used for identification of sulfur impurities, isopropylthiol (64 ppm) and diisopropyl sulfide(2.4 ppm), which were quantified by GC-AED. GC-AED also used for analysis of other impurities, nitrogen (54 ppm), hydrogen (2 ppm), oxygen (<1 ppm), carbon dioxide(30 ppm), carbon monoxide(<1 ppm), COS(32 ppm), methane(<1 ppm), and total sulfur(except the two sulfur compounds, 1 ppm). GC-FID was used for analysis of propane (108 ppm), propylene (70 ppm), and i-butane (9.5 ppm). FTIR was used for analysis of moisture (2155 ppm) to confirm the gas MS data. The two results gave different values for the moisture content. Gas MS data of moisture was used for purity calculation of H2S with uncertainty of 0.2%. Other uncertainty contribution to purity measurement of H2S was counted as 0.!%. Therefore, total of 0.3% of uncertainty was assigned to H2S purity result of 99.6%. KRISS primary reference gases(cylinder number, MD2547, MD2611, MD5850, MD5875) with 2% concentrations of H2S had been prepared by gravimetry; MD2547 ( %), MD2611 ( %), MD5850 ( %), MD5875 ( %). The 2% H2S in cylinder MD 2547 and MD 2611 were diluted to 10 ppm at Acculife cylinder which has specially treated inner surface for sulfur compounds. Scott cylinder number D and D were filled with 10 ppm H2S from dilution of MD2547 of 2% H2S. Cylinder number D and D were filled with 10 ppm H2S from dilution of MD2611 cylinder of 2% H2S; D (9.996 ppm), D ( ppm), D ( ppm), D ( ppm). D and D were selected as KRISS reference standard gas for K-41 inter-comparison work. Dilution system for making 10 ppm level H2S standard gases had been check for its cleanness (H2S contamination free) with flushing the system with N2 and collecting and analyzing the flushed N 2 which was collected in 6 L of Silco canister with pressure of 15 psig. The amounts of nitrogen used for balance gas were measured by gravimetry using high precision gas balance (Mettler, Switzerland) with readability of 1 mg and capacity of 10 kg. Luxfer cylinder (Australia) with fine-polished internal surface with stainless steel (SS) valve was used for the preparation of 2% level of H2S gas standards. For 10 ppm level of H2S gas standard, Acculife cylinder from Scott (Netherlands) cylinders were used. High purity nitrogen was used as balance gas (H2S impurities in the high purity nitrogen were checked using GC-AED) and The micro gas balance and gas balance was calibrated by E 2 grade calibration weight before starting measurement. Tare cylinder was used for buoyancy correction of gas weight measurement. Homogeneity of 2% level H2S gas standards has been check by GC-SCD (GC column used, 30 m x 0.32mm x 4 um, 5 ul of injection loop used for gas switching injection valve, 100 o C, sample split 30 : 1 at split injector, oven temp of 40 o C (4 min, isothermal), SCD burner temp 787 o C(pressure 252 psi), reactor temp 800 o C, SCD pressure 7.4 torr, column flow 2 ml/min, sample gas flow-rate of 60mL/min). Homogeneity of 10 ppm level H2S gas standards has been check by GC-AED at the same condition described above. Stability of 2% H2S standard gas was evaluated by comparing other KRISS H2S PRMs which was prepared in 2000 and New PRMs and old PRMs gave the same AED response factors with difference of 0.2%. Stability of 10 ppm H2S standard gas(prepared ) was evaluated by comparing with newly prepared 10 ppm PRM(prepared ). Old PRMs and new PRM gave the same AED response factors with difference of 0.2%. Loss of H2S due to adsorption to inner surface of cylinder was evaluated by distributing equal amount of 10 ppm H2S to other empty cylinder, then second cylinder again was distributed to another empty cylinder. The three cylinders were analyzed and compared their AED response factors to check the adsorption loss of H2S. Result showed that 0.015% loss at first distribution, 0.017% loss at second distribution. Instrument Calibration: Describe your Calibration procedure (mathematical model/calibration curve, number and concentrations of standards, measurement sequence, temperature/pressure correction etc.): Page 20 of 55

21 Two primary reference gas prepared as above was selected as standard for CCQM-K41 work, and one point calibration was used for the analysis since the prepared concentrations are very close to CCQM-K41 sample s concentration. At the same time, GC-AED analysis of H2S gave good linearity with passing origin always. KRISS H2S CRM conc.(umol/mol) k Uexp(umol/mol) Rel U(%) D D Analysis of KRISS primary reference gases and CCQM sample were repeated 8 times alternatively, and these are counted as one subset of measurement. Total of 6 subsets of measurement had been repeated which are counted as one set of measurement. Total of 5 sets of measurements had been repeated. Each analytical result of CCQM sample was obtained from the bracketed measurement of KRISS CRM to correct drift of GC-AED response. Lab temperature were kept 24 o C +_ 1 o C and atmospheric pressure were between 1000 ~ 1015 hpa. Since no appreciable change in temp and pressure were noticed, no correction for the temperature and pressure were made for the measurement. Sample Handling: How were the cylinders treated after arrival (stabilized) and how were samples transferred to the instrument (automatic, high pressure, mass-flow controller, dilution etc).: After receiving sample cylinder, box cartoon was opened, and cylinder was stored at room temperature before analysis (for 2 months). The sample cylinder was connected to GC-AED. The sample gas was transferred (with flow-rate of 100 ml/min) to gas sampling valve of GC. MFC was mounted between sample inlet-line and gas sampling valve to control constant flow of sample to the valve. Uncertainty: There are potential sources that influence the uncertainty of the final measurement result. Depending on the equipments, the applied analytical method and the target uncertainty of the final result, they have to be taken into account or can be neglected. Describe in detail how estimates of the uncertainty components were obtained and how they were combined to calculate the overall uncertainty: In support of this action, a list of potential uncertainty sources is given. This list may not be complete and is compiled from ISO-Standards, ISO-6142 and ISO a. Uncertainty related to the balance and mass pieces Readability of balance. 1 mg for gas balance, 0.01 mg for micro gas balance Accuracy of balance including linearity. 2 mg for gas balance, 0.04 mg for chemical balance Incorrect zero point. Negligible Drift (thermal and time effects). Negligible Instability due to draught. Negligible Location of cylinder on the balance pan: Negligible Always keep the cylinder positioned at the center of weighing pan. Balance has automatic centering function Errors in the mass pieces used. Not used Buoyancy effects on the weights used: Buoyancy was corrected using tare cylinder at each weighing procedure b. Uncertainties related to the gas cylinder Page 21 of 55

22 Mechanical handling of cylinder due to: loss of metal, paints or labels from surface of cylinder; Negligible loss of metal from threads of valve/fitting; Negligible dirt on cylinder, valves or associated fitting. Negligible Adsorption/desorption effects on the external cylinder surface. Negligible Weighing room was well air conditioned and kept temperature and humidity constant so that no absorption/desorption effects on the external cylinder surface. Buoyancy effects resulted from: the cylinder itself; differences in temperature of the cylinder from surrounding air due to e.g. filling with gas; After filling the cylinder with N2, the cylinder was stood at room temp until it cool down to room temp, and also kept at the weighing room for more than 4 hours before weighing change of cylinder volume during filling; Negligible Change of cylinder volume was checked by measuring the diameter of cylinder, but very little change was observed. change of density of air due to changes in temperature, air pressure, humidity, and carbon dioxide content. Temperature and humidity were constant during the weighing of cylinder. Buoyancy effect by air pressure change was corrected by using tare cylinder with same shape and weight. CO2 content of weighing room was also analyzed, and CO2 effect was negligible. Uncertainty in determination of external cylinder volume. Negligible c. Uncertainties related to the component gases Residual gas in cylinder. Cylinder used for KRISS CRMs for H2S were evacuated under oil-less high vacuum system (consisting turbo-molecular pump with diaphram pump backup). Leakage resulting from; leakage of air into the cylinder after evacuation; Negligible Leakage of the cylinder was check by reweighing the cylinder after evacuation (one day later). No leak was noticed leakage of gas from the cylinder valve during filling; Negligible Leakage of cylinder also was check by pressurizing the filling system and monitoring pressure change for a day. No pressure change was observed. escape of gas from cylinder into transport lines. Negligible Gas remaining in transfer system when weight loss method is used. Weight loss method does not used. Absorption/reaction of components on internal cylinder surface. Loss of 10 ppm level of H2S by adsorption or reaction on the surface of cylinder has been checked by filling to new evacuated cylinder with same specification. Absorption less than 0.1% could not be checked by analysis. Therefore, 0.1% uncertainty was counted as a loss due to absorption. Reaction between components. : No No other component except H2S and N2 was not found from H2S CRM. Impurities in the balance gase, N2 used. Less than 1 ppb of H2S High purity nitrogen with % purity was obtained from gas company, and the purity was checked by KRISS. Moisture, CO2, O2, Ar, CH4 were analyzed. Using the same analysis system, GC-AED, H2S was check down to ppb level. Impurities in H2S, 0.4% Insufficient homogenization. Negligible KRISS CRMs were sufficiently mixed after preparation using rolling mixer, then stood for a day at room temp before use. Uncertainty of molecular mass. Negligible Page 22 of 55

23 d. Uncertainties related to the analysis Repeatability and selectivity of the analyzer. Repeatability of GC-AED for 10 ppm level of H2S analysis was 0.2 ~ 0.4 %. Appropriateness of the calibration curve: response model and its residuals; Negligible mismatch of the sample gas and the calibration gas. Negligible Uncertainty related the corrections for the sampling: change in atmospheric pressure, temperature, sample flow rate, and sampling time. 0.1% Uncertainty sources with small contribution are not listed on following tables although the sources had been counted for uncertainty budget calculaltions. Uncertainty table: Hydrogen sulfide in N2 Uncertainty source Estimate X I Uncertainty of analysis, analytical response of sample, A sample Uncertainty of analysis, analytical response of standard, A x Factor related to purity of pure H2S chemical, fimp Factor related to adsorption loss in preparation of 10 ppm standard gas, fads10 Factor related to preparation homogeneity of 10 ppm standard gas, fhomo10 Factor related to stability of 10 ppm standard gas, fstab10 Factor related to preparation homogeneity of 2% standard gas, fhomo2 Factor related to stability of 2% standard gas, fstab2 x I Weighing uncertainty of 2% standard gas in preparation of 10ppm std gas, W g balh2s210 Uncertainty related to micro gas balance, Wug Uncertainty related to gas balance, Wg Uncertainty related to handling of sampling cylinder in micro balance measurement, Whadug2 Uncertainty related to handling of cylinder in weighing of std gas cylinder, Whad2 Assumed distributio n t- distrubuti on t- distrubuti on Standard uncertainty u(x i) Sensitivity coefficient c I Contribution to standard uncertainty u I(y) umol/mol x x normal normal t- distrubuti on normal t- distrubuti on normal t- distrubuti on 43 x 10-6 g mg normal 0.05mg 32 x mg normal 10 mg 522 x mg normal 0.05 mg 32 x mg normal 5 mg 522 x Page 23 of 55

24 Coverage factor or degree of freedom: k=2.0 or dof=193 Expanded uncertainty: 0.15 umol/mol Optional You may provide additional data like the raw measurement data, information on your measurement procedure etc: Preparation of 10 umol/mol level of H2S CRM and Analysis of K-41 sample. Model equation for CRM preparation and analyis C sample = (A sample /A x * x H2S10 ) * f press ; x H2S10 = (n H2S210 / n tot10 * ) * (f ads10 * f homo10 * f stab10 ); n tot10 = n H2S210 + n N212 + n N2dil ; n H2S210 = (m H2S210 / M toth2s10 ) * (x H2S2 /100) ; n N212 = (m H2S210 / M toth2s10 ) * (x N21 /100) ; n N2dil = m N2dil /M N2 ; M toth2s10 = M H2S * (x H2S2 /100) + M N2 * (x N21 /100) ; m H2S210 = (W balh2s210 + W ug / W hadug2 / ) ; m N2dil = (W baln2dil + W g / W had2 / 1000) ; x H2S2 = (n H2S2 / n tot2c * 100 ) * f purity * f homo2 * f stab2 ; x N21 = (n N21 / n tot2c * 100 ) ; n tot2c = n H2S2 + n N21 ; n H2S2 = m H2S2 / M H2S ; n N21 = m N21 / M N2 ; m H2S2 = (W balh2s2 + W g / W had2 / 1000) ; m N21 = (W baln21 + W g / W had2 / 1000) ; Page 24 of 55

25 List of quantities: Quantity Unit Definition C sample ppm conc of CCQM-41 from analysis A sample A x peak area from sample analysis peak area from standard analysis x H2S10 ppm conc of KRISS H2S std gas f press factor for pressure difference in sample introduction n H2S210 mole mole of H2S in 10 ppm std gas (kriss) n tot10 mole total mole of gases in 10 ppm H2S std gas f ads10 f homo10 f stab10 factor related to loss of H2S by adsorption in 10 ppm std gas uncertainty related to prep (homogeneity) of 10 ppm std gas uncertainty related to stability of 10 ppm H2S std gas n N212 mole mole of N2 contained 2% H2S used in preparation of 10 ppm H2S n N2dil mole mole of N2 used for preparation of 10 ppm H2S(as dilution gas) m H2S210 g wt(g) of 2% H2S gas taken for prep of 10 ppm gas M toth2s10 MW of 2% H2S x H2S2 % mole conc of H2S at 2% H2S gas x N21 % mole conc of N2 at 2% H2S gas m N2dil g wt of N2 dil gas in prep of 10 ppm gas M N2 M H2S MW of N2 MW of H2S W balh2s210 g wt of 2% H2S std gas taken for prep of 10 ppm gas W ug ug uncertainty related to chemical balance measurement W hadug2 ug uncertainty related to handling of cylinder in balance measurement W baln2dil g wt of N2 taken for prep of 10 ppm gas W g mg uncertainty related to chemical balance measurement W had2 mg uncertainty related to handling of cylinder in balance measurement n H2S2 mole mole of H2S used in 2% std gas n tot2c mole total mole of gases in 2% std gas f purity f homo2 f stab2 uncertainty of H2S purity uncertainty related to prep (homogeneity) uncertainty related to stability of 2% H2S std gas n N21 mole mole of N2 used in prep of 2% std gas m H2S2 g wt of H2S in prep of 2% std gas m N21 g wt of N2 used in prep of 2% std gas W balh2s2 g wt of H2S in prep of 2% std gas W baln21 g wt of N2 used in prep of 2% std gas Page 25 of 55

26 Uncertainty budget: Quantity Value Standard uncertainty Degrees of freedom Sensitivity coefficient Uncertainty contribution Corr.- coeff. Index A sample ppm A x ppm x H2S ppm ppm f press ppm n H2S mole n tot mole mole mole f ads ppm f homo ppm f stab ppm n N mole n N2dil mole mole mole m H2S g g M toth2s x H2S % % x N % % m N2dil g g M N ppm M H2S ppm W balh2s g g ppm W ug 0.0 ug 50.0 ug ppm W hadug2 0.0 ug 50.0 ug ppm W baln2dil g g ppm W g 0.0 mg 10.0 mg ppm W had2 0.0 mg 5.00 mg ppm n H2S mole mole n tot2c mole mole f purity ppm f homo ppm f stab ppm n N mole mole m H2S g g m N g g W balh2s g g ppm W baln g C sample ppm ppm g ppm Page 26 of 55