Report of key comparison CCQM K92

Transcription

1 Slovak Institute of Metrology Karloveská 63, SK Bratislava 4, Slovakia Report of key comparison CCQM K92 "Electrolytic conductivity at 0.05 S m -1 and 20 S m -1 Final report L. Vyskočil, M. Máriássy (SMU), Adrian Reyes, Marcela Monroy (CENAM), Alena Vospělová (ČMI), Bertil Magnusson, Rauno Pyykkö (SP), Elena Kardash (INPL), Fabiano Barbieri Gonzaga, I.C.S. Fraga, J.C. Lopes, W.B. Silva Jr, P.P. Borges, W.F.C. Rocha (INMETRO), Francesca Durbiano, E. Orrù (INRiM), Kenneth W. Pratt (NIST), Pia Tønnes Jakobsen, Hans Dalsgaard Jensen, Jørgen Avnskjold (DFM), L.A. Konopelko, Y.A. Kustikov, V.I. Suvorov (VNIIM), Song Xiaoping, Wang Hai (NIM), Steffen Seitz, Petra Spitzer (PTB), Vladimir Gavrilkin, Leonid Prokopenko, Oleksiy Stennik (Ukrmetrteststandart), Wladyslaw Kozlowski, Joanna Dumanska - Kulpa, Izabela Grzybowska (GUM), Yury A. Ovchinnikov (VNIIFTRI), Zsófia Nagyné Szilágyi, Judit Fükö (MKEH) July 2013

2 CCQM-K92 2 Abstract The aim of the key comparison CCQM-K92 was to demonstrate the capabilities of the participating NMIs to measure electrolytic conductivity of an unknown sample. Two samples with nominal electrolytic conductivity values of 0.05 S m -1 and 20 S m -1 have been prepared for comparison. For the first time conductivity value larger than those given in the IUPAC document [1] was measured in CCQM comparison. Thus no calibration standards with similar conductivity value were available. The comparison was an activity of the Electrochemical Working Group (EAWG) of the CCQM and was coordinated by SMU. In the comparison NMIs from fifteen countries took part. The higher conductivity (20 S m -1 ) was measured by ten participants. Good agreement of the results was observed for the majority of participants.

3 CCQM-K92 3 Contents ABSTRACT...2 INTRODUCTION...4 METROLOGY AREA...4 BRANCH...4 SUBJECT...4 TIME SCHEDULE...4 PARTICIPANTS...4 SAMPLE DESCRIPTION...5 SAMPLE PREPARATION AND DISTRIBUTION...5 REPLACEMENT SAMPLE PREPARATION...5 CHECK OF HOMOGENEITY...6 CHECK OF STABILITY...7 STATISTICAL TESTING OF STABILITY...9 RESULTS...10 SAMPLE WITH NOMINAL VALUE 0.05 S M SAMPLE WITH NOMINAL VALUE 20 S M DISCUSSION...14 THE FORMULAS FOR CALCULATION OF ESTIMATORS...14 CALCULATION OF THE DEGREES OF EQUIVALENCE...14 COMMUNICATION WITH THE PARTICIPANTS...15 REFERENCE VALUE FOR 0.05 S M Degrees of Equivalence S m REFERENCE VALUE FOR 20 S M Degrees of Equivalence - 20 S m CONCLUSIONS...19 ACKNOWLEDGMENT...19 REFERENCES...19 APPENDIX...20 ADDRESSES OF PARTICIPANTS...20

4 CCQM-K92 4 Introduction Metrology Area Amount of Substance Branch Electrochemistry Subject Determination of the electrolytic conductivity of two unknown samples with nominal value 0.05 S m -1 a 20 S m -1 (Water solution of KCl). Time schedule Dispatch of the samples 9 February 2011 Deadline for receipt of the report 25 April 2011 Discussion of results EAWG meeting, April 2011 Draft A report October 2011 Draft B report September 2012 Draft B report corrected February 2013 Participants Participants are listed in Table 1. VNIIM and VNIIFTRI measured one sample each, as their responsibilities are in different ranges in electrolytic conductivity. Table 1 Table of Participants N o Acronym Institute Country Contact Person 1 CENAM CENAM MEX Adrian Reyes, Marcela Monroy 2 CMI Český metrologický ústav CZE Alena Vospělová 3 DFM Danish Fundamental Metrology DNK Pia Tønnes Jakobsen 4 GUM Central Office of Measures POL Wladyslaw Kozlowski 5 INMETRO National Institute of Metrology, Quality and Technology BRA Fabiano Barbieri Gonzaga 6 INPL The National Physical Laboratory of Israel ISR Elena Kardash 7 INRiM Instituto Nazionale di Ricerca Metrologica ITA Francesca Durbiano 8 MKEH Hungarian Trade Licensing Office HUN Zsófia Nagyné Szilágyi 9 NIM National Institute of Metrology CHN Song Xiaoping 10 NIST National Institute of Standards and Technology USA Kenneth W. Pratt 11 PTB Physikalisch-Technische Bundesanstalt DEU Steffen Seitz 12 SMU Slovenský metrologický ústav SVK Leoš Vyskočil 13 SP SP Technical Research Institute of Sweden SWE Bertil Magnusson

5 CCQM-K UMTS Ukrmetrteststandart UKR Vladimir Gavrilkin 15 VNIIFTRI National Research Institute Physicotechnical and Radio Engineering Measurements RUS Yury A. Ovchinnikov 16 VNIIM D.I. Mendeleyev Institute for Metrology RUS Prof. L.A. Konopelko Sample description Sample preparation and distribution Samples consisted of water solutions of potassium chloride. Reagent grade KCl and distilled water were used for the solution with electrolytic conductivity 20 S m -1. The 0.05 S m -1 solution was prepared by diluting the above solution with distilled water. Both solutions were prepared on February 2, The solutions were filled into 500 ml HDPE bottles (Nalgene), which were subsequently sealed into aluminium laminated plastic foil to prevent composition change of the solutions. The samples were distributed to the participants on February 9, 2011 by courier companies FedEx and DHL (Russia, Mexico). In one case (NIM, China) the sample was received damaged. A replacement bottle was sent immediately and was received intact. The sample sent to Moscow stuck at the customs and was later returned to SMU. The second shipment arrived at its destination. Replacement sample preparation Some participants reported instability of 0.05 S m -1 sample after opening, and the same effect was confirmed by the coordinating laboratory. Therefore a new batch of this solution was prepared from high-purity KCl and deionised water and the new samples were distributed to the participants free of charge. The stability of new samples after opening was satisfactory. Check of the bottle integrity Participants were requested to weigh the received bottles to verify that they were unchanged during the transport. The mass change was smaller than 0.05 g in all cases except VNIIM, where the difference amounted up to 0.5 g, and NIM that reported one leaking bottle with KCl crystallisation in the bag. NIM was sent a replacement bottle. Figure 1 Relative differences between the weights of bottles - 0,05 S m -1

6 CCQM-K92 6 Relative differences between the weights of bottles - 0,05 S m -1 0,010% 0,008% 0,006% 0,004% 0,002% 0,000% -0,002% DNK MEX CZE POL BRA ISR ITA ITA HUN CHN DEU SVK SWE UKR RUS USA -0,004% -0,006% -0,008% -0,010% Figure 2 Relative differences between the weights of bottles - 20 S m -1 Relative differences between the weights of bottles - 20 S m -1 0,010% 0,008% 0,006% 0,004% 0,002% 0,000% -0,002% -0,004% -0,006% -0,008% -0,010% DNK DNK MEX POL BRA ISR HUN CHN DEU UKR RUS Check of Homogeneity Homogeneity of the solution was checked after filling. To identify possible trends, solutions from the first and the last bottle were measured. Both results were identical within uncertainty of measurement. The data are depicted in figures 3 and 4.

7 CCQM-K92 7 Figure 3 20,34 Check of homogeneity for 20 S m -1 solution Check of Homogeneity for 20,0 S/m 20,32 Conductivity ( S/m) 20,30 20,28 20,26 20,24 20,22 First bottle Last bottle 20,20 Figure 4 0,05020 Check of homogeneity for 0.05 S m -1 solution Check of Homogeneity for 0,05 S/m 0,05015 Conductivity ( S/m) 0, , , , ,04990 First bottle Last bottle 0,04985 Check of Stability Several bottles were selected for stability measurements. Samples were measured in irregular intervals during 80 to 90 days. The measurement results for solution with nominal conductivity 0.05 S m -1 are given in figure 5 and table 2. Figure 5 The stability measurement for sample with nominal conductivity value 0.05 S m -1

8 CCQM-K92 8 0,05020 Measurement of Stability for 0,05 S/m 0,05015 Conductivity S/m 0, , , , , Days Table 2 The stability Measurement for Sample with Nominal Value 0.05 S m -1 Days Date Bottle Conductivity (S.m -1 ) U (k=2) (S.m -1 ) B3 0, , B3 0, , B3 0, , B3 0, , B17 0, , B17 0, , B10 0, , B10 0, , The measurement results for solution with nominal conductivity 20 S m -1 are given in figure 6 and table 3. Figure 6 The stability measurement for sample with nominal conductivity value 20 S m -1

9 CCQM-K ,320 20,310 20,300 Measurement of Stability for 20 S/m Conductivity S/m 20,290 20,280 20,270 20,260 20,250 20, Days Table 3 The stability measurement for sample with nominal conductivity value 20 S m -1 Days Date Bottle Conductivity (S.m -1 ) U (k=2) (S.m -1 ) B9 20,288 0, B9 20,287 0, B9 20,287 0, B9 20,287 0, B9 20,288 0, B1 20,288 0, B1 20,288 0, B1 20,287 0, B1 20,287 0, B18 20,287 0, B18 20,287 0, B18 20,287 0, B24 20,288 0, B24 20,288 0,012 Statistical testing of stability The statistical testing of stability is based on the fact, that for a stable sample the is the trend statistically not significant. Either a test of correlation coefficient can be used the slope of a regression line can be tested. The procedure for the test of the slope is following: Using least-squares regression the slope b 1 of the regression line and residual variance s R are calculated. Test criterion t is calculated as follows:

10 CCQM-K92 10 ( x x) 2 b1 i t = (1) sr In the statistical tables for critical values of Student distribution a critical value t α (n-2) for (n- 2) degrees of freedom at significance level α=0,05 (95 % probability) is looked up. If the value of the test criterion does not exceed the critical value, the slope is statistically not significant. Table 4 Results of Statistical Testing of Stability Sample Value of Test. Criterion t Critical Value Degrees of Freedom Significance Level 0,05 S/m 0,779 2, ,05 20,0 S/m 1,241 2, ,05 Verdict No trend was observed No trend was observed As can be seen from the data in table 4, for both solutions the stability during the given time period was confirmed. Results Sample with nominal value 0.05 S m -1 The measurement conditions and methods used at different institutes are given in Table 5. The results of measurements of the new sample with nominal conductivity of 0.05 S m -1 are given in Table 6 and displayed graphically in Figure 7. Four laboratories from 15 used a primary measurement procedure. Table 5 Conditions of Measurement at Various Institutes S m -1 Institute Country Date of report Traceability Measurement frequency [Hz] DFM DNK Primary CRM DFM Jones type cell CENAM MEX SMU CRM Jones type cell CMI CZE Primary measurement Removable central part 1000 GUM POL DFM CRM Jones type cell INMETRO BRA Primary measurement Piston type INPL ISR SMU CRM Four electrode DC cell DC method

11 CCQM-K92 11 INRIM ITA Primary measurement Removable central part MKEH HUN OIML R56 Four electrode DC cell DC method NIM CHN IUPAC Jones type cell PTB DEU Primary measurement Piston type SMU SVK IUPAC Jones type cell 1000 SP SWE IUPAC WTW TetraCon 325? UMTS UKR Primary CRM UMTS Jones type cell 1000 VNIIFTRI RUS VNIIFTRI CRM Jones type cell? NIST USA Primary NIST CRM Daggett type cell Table 6 Results for sample with nominal value of electrolytic conductivity 0.05 S m -1 Institute Country EC 0,05 S/m u (k=1) INRIM ITA 0, , INMETRO BRA 0, , CMI CZE 0, , INPL ISR 0, , MKEH HUN 0, , GUM POL 0, , SMU SVK 0, , VNIIFTRI RUS 0, , DFM DNK 0, , NIST USA 0, , NIM CHN 0, , PTB DEU 0, , CENAM MEX 0, , SP SWE 0, , UMTS UKR 0, , Figure 7 The plot of results for sample with nominal conductivity value 0.05 S m -1 (standard uncertainty given)

12 CCQM-K ,0503 CCQM-K92 (Electrolytic Conductivity) - Nominal Value 0.05 S/m 0,0502 Electrolytic Conductivity / S m -1 0,0501 0,0500 0,0499 0,0498 ITA BRA ISR CZE HUN POL SVK RUS (VNIIFTRI) DNK USA CHN DEU MEX SWE UKR 0,0497 Sample with nominal value 20 S m -1 The measurement conditions and methods used at different institutes are given in Table 7. The results of measurements of the sample with nominal conductivity of 20 S m -1 are given in Table 8 and displayed graphically in Figure 8. Three laboratories from 10 used a primary measurement procedure. Table 7 Conditions of Measurement at Various Institutes - 20 S m -1 Institute Country Date of registered mail Traceability Measurement frequency [Hz] CENAM MEX SMU CRM Jones type cell GUM POL DFM CRM Jones type cell INPL ISR SMU CRM Four electrode DC cell DC method DFM DNK Primary CRM DFM Jones type cell VNIIM RUS IUPAC Jones type cell 1000 NIM CHN IUPAC Jones type cell MKEH HUN OIML R56 Four electrode DC cell DC method PTB DEU Primary measurement Piston type UMTS UKR Primary CRM UMTS Jones type cell 1000 INMETRO BRA Primary measurement Piston type

13 CCQM-K92 13 Table 8 Results for sample with nominal value of electrolytic conductivity 20 S m -1 Institute Country EC 20 S/m u (k=1) CENAM MEX 20,123 0,025 GUM POL 20,279 0,011 INPL ISR 20,280 0,014 DFM DNK 20,283 0,007 VNIIM RUS 20,290 0,007 NIM CHN 20,300 0,006 MKEH HUN 20,306 0,005 PTB DEU 20,308 0,007 UMTS UKR 20,344 0,004 INMETRO BRA 20,412 0,423 Figure 8 The plot of results for sample with nominal conductivity value 20 S m -1 (standard uncertainty given) CCQM-K92 (Electrolytic Conductivity) - Nominal Value 20 S/m 20,45 Electrolytic Conductivity / S m -1 20,40 20,35 20,30 20,25 20,20 MEX POL ISR DNK RUS (VNIIM) CHN HUN DEU UKR BRA 20,15 20,10

14 CCQM-K92 14 Discussion Nominal values of electrolytic conductivity of the samples were 0.05 S m -1 and 20 S m laboratories took part in the measurement of the 0.05 S m -1 sample. Sample with nominal value of electrolytic conductivity 20 S m -1 was measured by 10 laboratories. The Formulas for Calculation of Estimators κ Arithmetic Mean i κ = (2) n ( ) ( ) κi κ Standard Deviation of Arithmetic Mean uam = (3) n n 1 2 WM = wi xi Weighted Mean κ (4) 1 ui Calculation of Weights for Weighted Mean w = i (5) 2 1 ui wi xi xr Uncertainty of Weighted Mean uwm = (6) n 1 w 2 2 ( ( ) ) ( ) i Uncertainty of Median 1,858 u = median( κ ~ κ ) (7) i n 1 Calculation of the Degrees of Equivalence The degrees of equivalence for each participant, D i, and its standard uncertainty, u(d i ), are given by Eq 8 and Eq 9, respectively: ( KCRV) D κ (8) i = i

15 CCQM-K92 15 u 2 2 D = uκ + u KCRV i i (9) The standardized deviations E n are given by formula (10) E n = κ KCRV i U 2 κ i + U 2 KCRV (10) Communication with the participants DFM and NIST highlighted the instability of the first (0.05 S m -1 ) sample INRIM and UMTS were requested to check their results; no numerical error was found, but new results were sent in after recalibration of the cells. These new data are given in discussion only, as the original data have to be used. VNIIM was asked to correct the result for bottle weighing; corrected mass was sent. VNIIFTRI was requested to check its results; VNIIFTRI has found a mistake by transfer of value constant from primary to secondary cell and provided new results. CMI requested to postpone the deadline for internal reasons. Reference Value for 0.05 S m -1 Basic statistical data. Arithmetic mean S m -1 Standard uncertainty S m -1 Median S m -1 Standard uncertainty S m -1 The consistency information for different datasets is given in table 9. Table 9 Chi square values for nominal value S m -1 (values in bold are critical values)

16 CCQM-K92 16 Participants Degrees of freedom χ 2 - calculated χ 2 tabulated 95% probability Weighted mean Stand. uncertainty (Birge treatment) Birge Ratio All 14 78,437 23,685 0, , ,37 1,30 ITA excluded 13 52,656 22,362 0, , ,01 1,31 ITA, UKR excluded 12 22,171 21,026 0, , ,36 1,32 ITA, UKR, HUN excluded 11 12,627 19,675 0, , ,07 1,34 Numbers given in bold are tabulated data for 95 % probability and corresponding degrees of freedom. If ITA, UKR, HUN are not taken into account, the chi-squares value is smaller than the critical value. As a reference value KCRV = S m -1 (u = S m -1 ) was agreed. Degrees of Equivalence S m -1 Table 10 Degrees of Equivalence S m -1 Institute Country D i S/m U Di S/m INRIM ITA -0, , INMETRO BRA -0, , CMI CZE -0, , INPL ISR -0, , MKEH HUN -0, , GUM POL -0, , SMU SVK -0, , VNIIFTRI RUS -0, , DFM DNK -0, , NIST USA 0, , NIM CHN 0, , PTB DEU 0, , CENAM MEX 0, , SP SWE 0, , UMTS UKR 0, , Figure 9 Degrees of Equivalence for sample with nominal conductivity value 0.05 S m -1

17 CCQM-K ,0003 CCQM-K92 Degrees of Equivalence S/m 0,0002 Degrees of Equivalence 0,0001 0,0000-0,0001-0,0002-0,0003 ITA BRA ISR CZE HUN POL SVK RUS (VNIIFTRI) DNK USA CHN DEU MEX SWE UKR Reference Value for 20 S m -1 Basic statistical data. Arithmetic mean S m -1 Standard uncertainty S m -1 Median S m -1 Standard uncertainty S m -1 The consistency information for different datasets is given in table 11. Table 11 Chi square values for nominal value 20 S m -1 (values in bold are critical values) Participants Degrees of freedom χ 2 - calculated χ 2 tabulated 95% probability Weighted mean (S.m -1 ) Stand. uncertainty (Birge treatment) Birge Ratio All 9 192,287 16,919 20,3120 0,0096 4,62 1,37 UKR excluded 8 63,101 15,507 20,2945 0,0073 2,81 1,39 UKR, MEX excluded 7 15,528 14,067 20,2964 0,0039 1,49 1,42

18 CCQM-K92 18 Numbers given in bold are tabulated (critical) data for 95 % probability and corresponding degrees of freedom. If MEX, UKR are not taken into account, the chi-squares value is still slightly larger than the critical value. However, any further exclusion does not improve the chi-square value. As a reference value KCRV = S m -1 (u = S m -1 ) was agreed. Degrees of Equivalence - 20 S m -1 Table 12 Degrees of Equivalence 20 S m -1 Institute Country D i U Di S/m S/m CENAM MEX -0,173 0,051 GUM POL -0,017 0,023 INPL ISR -0,016 0,029 DFM DNK -0,013 0,015 VNIIM RUS -0,006 0,015 NIM CHN 0,004 0,014 MKEH HUN 0,009 0,013 PTB DEU 0,012 0,016 UMTS UKR 0,048 0,010 INMETRO BRA 0,115 0,845 CCQM-K92 Degrees of Equivalence - 20 S/m 0,20 0,15 0,10 Degrees of Equivalence 0,05 0,00-0,05-0,10-0,15 MEX POL ISR DNK RUS (VNIIM) CHN HUN DEU UKR BRA -0,20 Figure 8 Degrees of Equivalence for sample with nominal conductivity value 20 S m -1

19 CCQM-K92 19 Posterior work reported by DFM: DFM has since submitting K92 results and Draft A, examined the detailed frequency behaviour of its conductivity cells (cf. presentation EAWG/12-07 at CCQM-EAWG, Paris, April 2012). On this basis, we have shifted the frequency range used for extrapolation towards higher frequencies (towards lower phase angles) for measurements of high conductivity in the secondary cell, which provided traceability to the cell used at 20 S/m. The cell constant of the cell used in K92 at 20 S/m has thus been reevaluated and would today give a result with DoE of ± Conclusions Sixteen laboratories took part in the comparison, 15 measured sample with nominal conductivity of 0,05 S/m and 10 laboratories measured sample with nominal conductivity of 20 S/m. A good agreement of the results was observed for most laboratories. In some cases excessive uncertainty was due to measurement of very small resistance (less than 0,1 Ω) due to low cell constant of the conductivity cells used. In the case of measurements of sample with conductivity ~20 S/m in secondary cells there could be some problems with calibration, as CRMs with such a high conductivity are not commonly available. These measurements thus can be classified as extrapolation measurements. How far the light shines statement: The results in this comparison on the 0.05 S/m solution can be considered to be representative for measurement capabilities in the range from S/m to 0.15 S/m. The results in this comparison on the 20 S/m solution can be considered to be representative for measurement capabilities in the range from 6 S/m to 25 S/m. Due to the increased difficulty associated with performing the measurement as the conductivity increases, for the range from 25 S/m to 60 S/m the results from this comparison are to be complemented in the review process by a detailed technical evaluation of the measurement procedure. Acknowledgment The coordinating laboratory gratefully acknowledges the contributions of all participants and of the members of the CCQM Working Group on Electrochemical Analysis for their valuable suggestions concerning the measurement protocol and the evaluation process. References 1. Pure Appl. Chem., Vol. 73, No. 11, pp , Final Report for Key Comparison CCQM-K36, available at 3. Final Report for Key Comparison CCQM-K36.1, available at

20 CCQM-K92 20 Appendix Addresses of participants Adrian Reyes, Marcela Monroy CENAM Km 4.5 Carretera a los Cues, Mpio. El Marques, Queretaro, Mexico. CP MEXICO Alena Vospělová Český metrologický ústav (ČMI) Okružní Brno CZECH REPUBLIC Bertil Magnusson SP Technical Research Institute of Sweden Brinellgatan Borås SWEDEN Elena Kardash The National Physical Laboratory of Israel (INPL) Danciger A bldg., Givat-Ram, Jerusalem, 91904, ISRAEL Fabiano Barbieri Gonzaga National Institute of Metrology, Standardization and Industrial Quality - INMETRO Av. Nossa Senhora das Graças, 50, Xerém Duque de Caxias, RJ, Brazil BRAZIL Francesca Durbiano Instituto Nazionale di Ricerca Metrologica (INRiM) Strada delle Cacce 91, CAP 10135, Torino, ITALY Kenneth W. Pratt National Institute of Standards and Technology Building 227, Room B Bureau Dr., Stop 8391 Gaithersburg, MD U.S.A. Leoš Vyskočil

21 CCQM-K92 21 Slovak Institute of Metrology Karloveska 63, SK Bratislava SLOVAKIA Pia Tønnes Jakobsen Danish Fundamental Metrology A/S (DFM) Matematiktorvet 307, DK-2800 Kgs. Lyngby DENMARK Prof. L.A. Konopelko D.I. Mendeleyev Institute for Metrology (VNIIM) 19, Moskovsky pr., St. Petersburg, RUSSIA Song Xiaoping National Institute of Metrology (NIM) No. 18, Bei San Huan Dong Lu, Beijing , P.R.CHINA Steffen Seitz Physikalisch-Technische Bundesanstalt (PTB) Fachbereich 3.1 Bundesallee Braunschweig GERMANY Vladimir Gavrilkin Ukrmetrteststandart Metrologichna str.,4 Kiev, UKRAINA Wladyslaw Kozlowski Central Office of Measures (GUM) Laboratory of Electrochemistry Elektoralna Str Warsaw, POLAND Yury A. Ovchinnikov VNIIFTRI (National Research Institute Physicotechnical and Radio Engineering Measurements) , Mendeleevo, Moscow region, Russia VNIIFTRI, Lab 35 RUSSIA