International Comparison CCQM K53 Oxygen in Nitrogen

CCQM-K53 Final Report International Comparison CCQM K53 Oxygen in Nitrogen Jeongsoon Lee 1, Jin Bok Lee 1, Dong Min Moon 1, Jin Seog Kim 1*, Adriaan M.H. van der Veen 2, Laurie Besley 3, Hans-Joachim Heine 4, Belén Martin 5, L.A. Konopelko 6, Kenji Kato 7, Takuya Shimosaka 7, Alejandro Perez Castorena 8, Tatiana Macé 9, Martin J.T. Milton 10, Mike Kelley 11, Franklin Guenther 11, Angelique Botha 12 1 Korea Research Institute of Standards and Science (KRISS), Division of Metrology for Quality Life, P.O.Box 102, Yusong, Daejeon, Republic of Korea 2 VSL, Thijsseweg 11, 2629 JA Delft, the Netherlands 3 National Measurement Institute, Australia (NMIA), Bradfield Road, West Lindfield, Lind-field, NSW 2070, Australia 4 Bundesanstalt für Materialforschung und prüfung (BAM), Abteilung I, Unter den Eichen 87, D-12205 Berlin, Germany 5 Centro Espanol de Metrologia (CEM), C/ del Alfar, 2, 28760 Tres Cantos (Madrid), Spain 6 D.I. Mendeleyev Institute for Metrology, Rostekhregulirovaniye of Russia (VNIIM), Department of State Standards in the field of Physical Chemical Measurements, 19, Moskovsky Prospekt, 198005 St- Petersburg, Russia 7 National Metrology Institute of Japan (NMIJ), Tsukuba Central 3, Tsukuba 305-8563, Japan 8 CENAM, Km. 4,5 Carretera a los Cues, Municipio del Marques C.P. 76900, Queretaro, Mexico 9 Laboratoire national de metrologie et d'essais (LNE), rue Gaston Boissier - 75724 Paris Cedex 15, France 10 National Physical Laboratory (NPL), Teddington, Middlesex, TW11 0LW, UK 11 National Institute of Standards and Technology (NIST), Chemical Science and Technology Laboratory, 100 Bureau Drive, Gaithersburg MD, USA 12 National Metrology Institute of South Africa (NMISA), Meiring Naude road, Building 4, Room W14, 0001 Pretoria, South Africa 1

Field Amount of substance Subject Oxygen 100 level in Nitrogen Participants Total 12 NMIs have taken part in this comparison. The participants are listed in table 1. Table 1: List of participants Acronym Country Institute NMIA AU National Metrology Institute of Australia, Linfield, Australia BAM DE Bundesanstalt für Materialforschung und prüfung, Berlin, Germany CEM ES Centro Espanol de Metrologia, Madrid, Spain LNE FR Laboratoire National d'essais, Paris, France NMIJ JP National Metrology Institute of Japan, Tsukuba, Japan KRISS KR Korea Research Institute of Standards and Science, Daejeon, Republic of Korea CENAM MX Centro Nacional de Metrologia, Queretaro, Mexico VSL NL VSL, Delft, the Netherlands VNIIM RU D.I. Mendeleyev Institute for Metrology, St. Petersburg, Russia NPL UK National Physical Laboratory, Teddington, Middlesex, United Kingdom NIST US National Institute of Standards and Technology, Gaithersburg, United States of America NMISA ZA National Metrology Institute of South Africa, Pretoria, South Africa Organizing body CCQM Introduction Gravimetry has been used as the primary method for the preparation of primary standard gas mixtures in most of NMIs [1], which requires the complete abilities of the 2

purity assessment, weighing technique and analytical skills. At the CCQM GAWG meeting in October 2005, it was agreed that KRISS coordinates a key comparison on the gravimetric preparation of gas, at a level of 100 of oxygen in nitrogen. KRISS compared the gravimetric value of each cylinder by an analytical instrument. A preparation for oxygen gas standard mixture requires a particular notice to be accurate, because it is a major component of atmosphere. Key issues for this comparison are related to (1) gravimetric technique which needs at least two steps for dilution, (2) oxygen impurity in nitrogen, and (3) argon impurity in nitrogen. Support for CMC claims This key comparison will support claims for capability to perform a gravimetric preparation, including purity assessment, on primary gas mixtures from 10 to 10 mmol/mol of oxygen in nitrogen. As a result of the comparison, CMCs can also be recognised for stable gas species, such as argon, neon, helium, hydrogen, in nitrogen because of similarity in the preparation and purity measurement processes. Schedule Jan. 15, 2007 Shipment of cylinders from participants to KRISS Feb. 1 ~ Mar. 31, 2007 Measurement of oxygen and argon amount in cylinders by KRISS 2007 CCQM/GAWG April meeting Draft A report 2008 CCQM/GAWG Fall meeting Discussion on a KCRV determination Design of the key comparison For this key comparison, participants were divided in three groups according to the nominal mole fraction of oxygen in nitrogen and prepared their standard mixtures of the appointed amount of substance fraction of oxygen in nitrogen, as shown in table 1. The amount-of-substance fractions of oxygen had to be in the range of 98 to 102. Table 2: the three groups of participants and their nominal mole fraction of oxygen in nitrogen appointed for CCQM-K53. Nominal Oxygen amount Participating NMI fraction in Nitrogen [] 3

Group A 99 NMIJ, NPL, BAM Group B 100 CEM *, NMIA, NIST, NMISA, LNE ** Group C 101 CENAM, KRISS, VNIIM, VSL * CEM announced to have an error in their data, so the CEM result was not used for the evaluation of the KCRV. ** LNE was appointed to prepare 100, but they sent the gas cylinder with the amount of the oxygen fraction of 101 to the coordinating lab. Participating laboratories had to report weighing method in detail and all of related data including a detailed description of the uncertainty budget and send the cylinders to the coordinating laboratory with a sufficient amount of gas left (pressure of at least 5 MPa). After receiving all cylinders from participants, the coordinating laboratory compared each cylinder. Verification of analytical procedures KRISS has reported a measurement capability at a mole fraction of 100 oxygen in nitrogen measured with a gas chromatography (GC)/thermal conductivity detector (GC/TCD) and a GC/atomic emission detector (AED) including assessment of argon impurity during CCQM/GAWG meetings. A modified GC/TCD was used as an analyzer for this comparison. During this comparison, the measurement reproducibility with the GC/TCD was kept within 0.06 % (relative standard deviation). In order to check an internal consistency, a series of 4 mixtures with mole fractions between 98 and - 102 of oxygen in nitrogen were prepared gravimetrically. One out of 4 cylinders (A, B, C, D) was chosen as reference cylinder (A), the others were analyzed against the reference. Each cylinder was measured three times against the reference cylinder, according to the following sequence (for cylinder B) : A-B-A-B-A- B-A to compensate the drift of the GC/TCD analyzer. It is well known that GC-TCD shows a good linearity within a wide range. Introducing an oxygen null gas into a sample inlet, the response of a chromatogram recorded with a GC/TCD analyzer is negligible enough that it is extrapolated to origin. Therefore, a calibration curve was forced to go through origin with 4 points. The curve including origin prevents KCRV from getting into some accidental deviation caused by any wrong cylinder. Hence the predicted mole fraction (x pred ) in table 3 has been calculated on the basis of an unweighted ordinary linear least squares (OLS) regression including origin, as the uncertainty of y is the same for all points. The measurement data (x prep, y) are in Table 3 and the result is shown in Eq. 1 and Fig. 1. The value of y-intercept in Eq. 4

1 shows a deviation of 0.0000005±0.0000857, which is much less than the value of reproducibility of the analyzer. y = (0.0100162 ± 9.5 10-7 ) x + (0.0000005±0.0000857) (R 2 = 0.99999, N=5). (Eq. 1) In table 3, the following data are summarized x prep mole fraction, from preparation (10-6 mol/mol) u (x) standard uncertainty of xprep (10-6 mol/mol) y response ratio against the reference cylinder (ME5662) with GC/TCD u (y) standard uncertainty of y x pred x calculated value using linear regression equation (Eq. 1) (10-6 mol/mol) difference between x pred and x prep (10-6 mol/mol). Table 3: analysis of the four primary reference cylinders of oxygen in nitrogen prepared by KRISS Cylinder # x prep [] u (x) using a GC/TCD analyzer [] y (1) u (y) x pred [] x (=x pred - x prep ) [] ME5662 99.841 0.011 1.00000 0.0006 99.836-0.005 ME5648 100.626 0.010 1.00785 0.0006 100.620-0.006 ME5697 101.053 0.010 1.01200 0.0006 101.054 0.001 ME5097 101.017 0.011 1.01185 0.0006 101.019 0.002 (1) Response ratio against the reference cylinder, ME5662. Two standard deviations in table 3 are taken as the uncertainty of preparation (0.01 %) and the uncertainty of the analysis (0.06 %), respectively. This linear regression analysis looks reasonable in that the maximum deviation value ( x = -0.006 ) is sufficiently less than the value of the preparation uncertainties (0.022 ). Based on the residuals satisfy the following requirements based on ISO 6143[4]. x k u x ), (Eq. 2) i ( i where k denotes coverage factor and u(x i ) the standard uncertainty associated with x i. As a result of the regression analysis for 5 points including origin, the regression analysis indicates that any influential systematic error during this work may not be engaged. 5

Accordingly, this regression analysis demonstrates the internal consistency between the standard mixtures prepared by KRISS. Figure 1: Linear regression of 4 calibration points for quality control Measurement of oxygen in nitrogen The measurement of oxygen in nitrogen was carried out using a HP6890 GC analyzer, equipped with a modified TCD detector and a sampling valve line without an injection port. The sampling valve is directly connected to the column to remove possible dead volume. The column used was a Molsieve 5A, 4 m, OD 1/8", 80-100 mesh. Helium was used as carrier gas, with a flow of 28 ml/min. Samples passed through a Multi Position Valve (MPV) directly connected to each cylinder, then through a mass flow controller to be finally introduced in the sample loop (Fig. 2). Two pressure restrictors were adopted to provide damping effect and to maintain a constant pressure in the TCD detector and in the sample loop before venting to the atmosphere. For the purpose of checking possible leakages and optimizing the sensitivity of the system, we had operated it over a week with the MPV connected to the cylinders. As a result, the optimized experimental conditions in the GC system were fixed at a sample flow rate of 250 ml/min with a volume of 5 ml. In case that the peak of argon can not be separated from that of oxygen under these conditions, other experimental conditions were sought by lowering the temperature of the GC column in oven. Two examples of experimental conditions which enable the oxygen peak in the chromatogram to be resolved from the argon peak are presented in table 4. 6

Figure 2: Schematic diagram of the experimental setup During the measurement of each cylinder, the pressure restrictors were adjusted to a pressure of 1.9 bar, which ensured the pressure in the sample loop to be constant. The sample loop was continuously rinsed (except when injecting). As a rule, it takes 20 minutes to obtain one data point and most of the time was consumed in the process of heating and cooling the oven to separate argon and oxygen. Table 4: Analytical conditions for two different cases Condition 1 Condition 2 Detector TCD (modified) " Dec. temp. 275 " Carrier flow 28 ml/min (50 psi) " Ref. flow 45 ml/min " Column Resteck Molesieve 5A 4m, 1/8", SS " Oven temp. -15, 13.5 min 30 /min 225, 7 min -33, 19 min 30 /min 225, 7 min Oven equilibrium time 5 min " Valve box temp. 75 " Sample flow 250 ml/min " Sample loop 5 cc " 7

In addition, in between each cylinder the reference cylinder A was measured to correct for the drift of the analyzer during the time of the comparison (sequence A-B-A-C-A-...). Two standard mixtures (CC245834 and PC6082, volume of 30 L), of a nominal mole fraction of 100 prepared by KRISS with the gravimetric method were used during the entire comparison period as working standards. To assess the repeatability, the measurement of each sample was repeated three or five times. Considering repeatability, drift and reproducibility, the analyzer response ( y, ) of i-th NMI cylinder is expressed as Eq 3. y J = ( yrespons, i, S /( y y J j ref, i 1, S + j ref, i 1, S ) / 2), (Eq. 3) j responscor r, i + / S j = 1 responscorr i where y, respons i S j, is measurement response of i-th NMI during S j th series measurement; y ref i 1, S j, and y ref i 1, S j, + denote the response of standard reference cylinder of CC245834 (or PC6082) before and after measurement of a i-th NMI to control a drift. S j denotes j-th series measurement and j ranges from 1 to J. It means that a series of measurement was repeated J times for reproducibility before obtaining the final response value. Actually all measurements for NMI cylinders performed 3-4 times from first of March to 13 th of March. From Eq. 3. the analysis uncertainty is obtained. For example of KRISS cylinder, the standard uncertainties were ranged from 0.00015 to 0.000885 during four sequent measurements and its final uncertainty for J=4 was calculated as 0.00014 listed in Table 7. 8

Results 1. Argon impurity The mole fraction of argon in nitrogen was measured in all of standard gas mixtures submitted by NMIs so as to examine the level of impurities. (Argon amounts in each cylinder ranged from 0.21 to 293.38.) The amount of argon deduced from the ratio between the peak of argon and the peak of oxygen in each chromatogram, as thermal conductivity detectors generally show a very stable linear response. Because the high mole fraction of argon present in the cylinders caused an interference between the argon and oxygen peaks, during experiment by means of GC, the peak of oxygen was explicitly separated by that of argon (Fig. 3) with two analytical conditions as summarized in table 4. 2 5 u V T C D 2 B, ( 0 7 0 3 1 1 \ M E 5 6 9 7 0 3. D ) KRISS, Ar = 2.32 2 5 u V T C D 2 B, ( 0 7 0 3 1 5 \ N M I A 0 0 0 4. D ) NMIA, Ar =293.38 1 0 0 8 0 Nitroge 1 0 0 8 0 6 0 6 0 O2 4 0 4 0 O2 2 0 2 0 Ar 0 0 5 1 0 1 5 2 0 2 5 N2-15, 13.5 min m i n 0 0 5 1 0 1 5 2 0 2 5 Ar N2-33, 19 min m i n Figure 3: Chromatograms for two gas mixtures (KRISS and NMIA) measured with GC/TCD Table 5 shows the Ar measurement results. Nine cylinders were analyzed with condition I and Argon was measured with mole fractions in the range of 0.21-14.03, while three cylinders were with condition II and Argon was found with mole fractions greater than 100. During all analysis, the standard deviation (1σ) on four repeats was within the maximum of 0.68 (Table 5). The results of the measurement show complete separation of argon and oxygen by the GC method, so we can conclude that the results for oxygen are not affected by the presence of argon irrespective of the amount of argon present. 9

Table 5: Summary for argon amounts in each mixture Cylinder Ar conc.() received from 1 2 3 4 average σ NMIJ 0.22 0.21 0.23 0.21 0.21 0.01 NPL 1.26 1.32 1.30 1.30 1.29 0.03 BAM 1.52 1.53 1.54 1.50 1.52 0.02 CEM 4.63 4.58 4.65 4.61 4.62 0.03 NMIA 293.84 293.87 292.41 293.39 293.38 0.68 NIST 14.07 14.06 14.02 14.03 14.05 0.03 NMISA 117.58 117.57 117.03 117.07 117.31 0.30 CENAM 102.43 102.36 101.70 101.85 102.08 0.36 LNE 4.57 4.58 4.59 4.62 4.59 0.02 KRISS 2.15 2.39 2.35 2.35 2.32 0.09 VNIIM 3.07 3.14 3.07 3.08 3.09 0.03 VSL 0.26 0.24 0.23 0.23 0.24 0.01 10

2. Results of Oxygen comparison In the comparison a degree of equivalence (D i ) is defined [3,4] as the difference of a measurement result with respect to the key comparison reference value (KCRV) [17,18] and its associated uncertainty. x i = D i = x i,prep x i,kcrv (Eq. 4) where x i,kcrv and x i,prep denotes the key comparison reference value and the preparation value of i-th NMI, respectively. Here a key comparison reference value, x i,kcrv is replaced with x i,ref in this comparison as a matter of convenience. When considering the non independence of the reference value on the contributing laboratories, the covariance between the value submitted by the laboratory and the reference value has to be taken into account for the calculation of u(d i ). Here a contributing laboratories indicates a dataset which participate the KCRV determination. In this case a degree of equivalence is expressed as Eq. 5. x i,adj is completely different from the following x i,pred (Eq. 10) physically in that x i,adj and x i,pred provide the difference based on orthogonal and horizontal projection, respectively. D i = x i,prep - x i,adj. (Eq. 5) In order to obtain x i,adj, a general least square method such that the corresponding sum of squared deviations between each preparation data point ( x y ) and an adjusted data point ( x ˆ, yˆ ), weighted by the inverse squares of the associated uncertainties, is a i i minimum is used as a rule. i, i n 2 2 2 x ˆ ˆ i xi yi yi χ = + = min 2 2 (Eq. 6) i= 1 u ( xi ) u ( yi ) Here it is expected the coordinates ( xˆ, yˆ ) in the equation (6) to satisfy the regression relation (Eq. 7). yˆ i a + 1 a2xˆ i i i =, (Eq. 7) which has been chosen as model in this case. Minimizing χ 2 leads to the values for the model parameters a 1 and a 2, which are obtained by computation of Eq. 6 with GLS (general least square). In ISO 6143 [4] the procedures on parameter evaluation are explained. The functional relationship (Eq. 6) indicates that the smaller uncertainty of the submitted value (x prep and u(x prep )), the more weight in the least-square fit. Uncertainty associated with degrees of equivalence can be obtained from the uncertainties of the adjusted and prepared point, taking also into account the covariance 11

( u x i, xˆ ) ) between them. Its expression is: ( i 2 2 u( x) = u ( x ) + u ( xˆ ) 2 u( x, xˆ ). (Eq. 8) i i Only 8 among 12 participants were chosen to contribute to the KCRV calculation, with the consequence that the following data points have been removed: (1) The CEM value, as it had been declared by them to be in error, (2) the NMISA, VNIIM, NMIA values, as they were inconsistent with the others owing to their ambiguity in impurity analysis. i i Table 6 summarizes the results for this comparison. In the table, the mole fraction (x prep ) together with its expanded uncertainty (U(x prep )) which was prepared by each NMI and the analyzer response value (y) along with its standard uncertainty (u(y)) which were measured by coordinating Lab. are presented. The response values have no need to be corrected for any pressure influence, because the pressure of the measurement system has been kept constant by means of the pressure restrictor. The column of U( x) denotes the expanded uncertainty with 95 % confidence level. The adjusted mole fraction (x adj ) of Table 6 has been obtained on the basis of a general linear least square (GLS, XGenLine [5]) regression with the origin point, that is (0 ± 0.01, 0 ± 0.0006), where 0.01 and 0.0006 are from table 3. This selection of regression line with the origin point, which was also supported by the internal validation results, helps the regression line not to be affected by some points which are suspected to be highly deviated from the line. Accordingly, the 9 values including both the KCRV subset and an origin are participated in the process of KCRV determination. The results of KCRV subset laboratories are given in bold in table 6. The regression model line of the computation reads as follows: y = ( 0.0099583 ± 0.0000066) x + (0.000014 ± 0.000608), (N=9, including origin). (Eq. 9) The numbers in the parenthesis represent the standard deviations of the slope and the intercept, respectively. The covariance between parameters is -3.59 10-9. Figure 4 shows the least square regression line and the data points (x prep, y). All bars in all data points in the figure present x-direction and y-direction expanded uncertainties (k = 2), respectively. On the contrary, the degree of equivalence of the other four laboratories, which were not included among the KCRV subset, is derived from the vertical deviation from the regression line of Eq. 9. The results of these laboratories 12

are written in table 6 where the uncertainty of the difference is given as 2 2 u ( xi ) = u ( xi, prep) + u ( xi, pred ), where x i, pred y a a i 1 =. (Eq. 10) 2 The deviations between the adjusted points or the predicted values and the preparation values originally submitted and the corresponding uncertainties of their deviations calculated for both contributing and the non-contributing laboratories are shown in Fig. 5. Their uncertainties are given as 95% confidence intervals, as shown in table 6. The result shows that most of the KCRV dataset are consistent with KCRV considering their uncertainties, that is, the criterion (ISO 6143 [4]) x k u x ) (k = 2) (Eq. 11) i ( i is satisfied for 7 data points. The parameter En in the last column of table 6, the deviation divided by its expanded uncertainty, is introduced to examine the agreement with the KCRV. En of table 6 shows that most of the KCRV subset is within the limit of unity, only LNE deviate from the KCRV slightly. In Fig. 5, the uncertainties of deviations of NMIJ and KRISS come to be fairly smaller than the submitted uncertainties because of the covariance term of Eq. 8. Fig. 6 shows the relative deviation and its uncertainty (k=2) of each NMI. The figure indicates that the contributing laboratories (the KCRV subset) agree well with the KCRVs compared to the others. In addition, the figure shows that all residuals in the KCRV subset (except LNE) well satisfy the above consistency criterion (Eq. 11) of ISO 6143 [4]. The degree of equivalence and its uncertainty obtained by this approach can give a typical representation of a preparative and analytical capability when evaluating CMCs in the same way. 13

Figure 4: Linear regression of oxygen data; error bar denote U of the point. Figure 5: Graph of equivalence for CCQM-K53 14

Table 6: Full data set of CCQM-K53 results x prep U(x prep ) x adj u(x adj ) x pred u(x pred ) x ( D i ) U( x), k=2 NMI y u(y) [] [] NMIJ 98.675 0.018 0.983020 0.0006 98.676 0.009-0.001 0.002-0.398 NPL 99.002 0.096 0.986981 0.0006 99.045 0.039-0.043 0.056-0.767 BAM 99.17 0.25 0.986377 0.0006 99.072 0.059 0.098 0.231 0.424 CEM 100.040 0.023 0.994595 0.0006 99.875 0.066 0.165 0.134 1.23 NMIA 100.10 0.14 1.000875 0.0006 100.515 0.067-0.415 0.193-2.15 NIST 100.41 0.12 0.998881 0.0006 100.359 0.045 0.051 0.081 0.633 NMISA 100.585 0.022 1.005079 0.0006 100.929 0.067-0.344 0.135-2.54 CENAM 100.97 0.30 1.006298 0.0006 101.039 0.061-0.069 0.274-0.252 LNE 101.04 0.10 1.004614 0.0006 100.974 0.040 0.066 0.059 1.11 KRISS 101.053 0.020 1.006739 0.0006 101.054 0.010-0.001 0.004-0.244 VNIIM 101.08 0.14 1.009951 0.0006 101.417 0.067-0.337 0.194-1.73 VSL 101.15 0.08 1.007570 0.0006 101.159 0.034-0.009 0.040-0.226 E n 15

Figure 6; Relative degrees of equivalence for CCQM-K53 Conclusion This key comparison focuses a comparison to evaluate the capability for the preparation and the analysis of the stable gas species in nitrogen. The target amount of substance is 100 of oxygen in nitrogen. The oxygen primary standard gas mixtures were prepared gravimetrically through at least two or three steps for dilution with the range of preparation uncertainty, 0.009 to 0.15 (1 σ). As a result they are consistent with each other within the maximum deviation of 0.42. The reference value is obtained from the linear regression line (with origin) of a selected set of participants. The KCRV subset except one agree with each other. The standard deviation of the x- residuals of them (which consists of NMIJ, VSL, NIST, NPL, BAM, KRISS, and CENAM) is 0.056 and well consistent with the uncertainties given to their standard mixtures. The standard deviation of the residuals of all participating laboratory is 0.182. 16

With respect to impurity analysis, overall Ar amounts of the cylinders are in the range of about 3, however four cylinders showed Ar amount fraction over 10. Two out of them are inconsistent with the KCRV subset. The explicit separation between two peaks of oxygen and argon in the GC chromatogram is essential to hold analytical capability. Additionally oxygen impurity analysis in nitrogen is indispensable to ensure the preparative capability. References [1] Alink A., The first key comparison on Primary Standard gas Mixtures, Metrologia 37 (2000), pp. 35-49 [2] International organization for standardization, ISO 6142, Gas analysis, Preparation of calibration gas mixtures, Gravimetry method, ISO, Second edition, 2001(E) [3] Van der Veen A.M.H., Brinkmann F.N.C., Arnautovic M., Besley L., Heine H.-J., Lopez Esteban T., Sega M., Kato K., Kim J.S., Perez Castorena A., Rakowska A., Milton M.J.T., Guenther F.R., Francy R., Dlugokencky E., International comparison CCQM-P41 Greenhouse gases. 2. Direct comparison of primary standard gas mixtures, Metrologia 44 (2007), Techn. Suppl. 08003 [4] International organization for standardization, ISO 6143, Gas analysis, Comparison methods for determining and checking the composition of calibration gas mixtures, ISO, Second edition, 2001(E) [5] Milton M.J.T., Harris P.M., Smith I.M., Brown A.S., Goody B.A., Implementation of a generalized least-squares method for determining calibration curves from data with general uncertainty structures, Metrologia 43 (2006), pp. S291-S298 17

Annex 1: Measurement raw data of Oxygen Table 7: Raw data of Oxygen for CCQM-K53 Response of measurements NMIs 1 2 3 4 mean σ Conc. prep [] Unc. prep (k=2) [] NMIJ 0.982682 0.983252 0.983121 0.983025 0.98302 0.00024 98.675 0.018 NPL 0.987026 0.987053 0.986890 0.986956 0.98698 7.3E-05 99.002 0.096 BAM 0.986367 0.986426 0.986375 0.986339 0.98638 3.6E-05 99.17 0.25 CEM 0.994491 0.994663 0.994630 0.99460 9.1E-05 100.040 0.023 NMIA 1.001387 1.000263 1.000898 1.001464 1.00100 0.00055 100.10 0.14 NIST 0.998233 0.998882 0.999153 0.999257 0.99888 0.00046 100.41 0.12 NMISA 1.004520 1.005936 1.005266 1.004593 1.00508 0.00066 100.585 0.020 CENAM 1.006595 1.006092 1.006264 1.006243 1.00630 0.00021 100.97 0.30 LNE 1.004460 1.004737 1.004640 1.004640 1.00462 0.00012 101.04 0.10 KRISS 1.006601 1.006932 1.006772 1.006651 1.00674 0.00015 101.053 0.020 VNIIM 1.009659 1.009951 1.010556 1.009636 1.00995 0.00043 101.08 0.14 VSL 1.007986 1.007479 1.007219 1.007595 1.00757 0.00032 101.15 0.08 18

Report form CCQM-K53 (Oxygen in Nitrogen) Date: 18 Oct. 2006 Laboratory: National Metrology Institute of Japan Prepared 99 oxygen gas Cylinder Number: CPC00641 Amount fraction of oxygen: 98.675 Coverage factor: 2 Expanded uncertainty: 0.018 Results of determinations Purity of nitrogen: 999999.5 10-6 mol/mol Component Amount fraction Standard Assumed 10-6 mol/mol Uncertainty distribution Oxygen 0.0031 0.00013 Normal Argon 0.017 0.0098 Rectangle Carbon monoxide 0.0078 0.0045 Rectangle Carbon dioxide 0.0090 0.0064 Normal Methane 0.0022 0.0013 Rectangle Nitrous oxide 0.00049 0.00028 Rectangle Water 0.44 0.25 Rectangle Nitrogen 999999.5 0.25 Normal Purity of oxygen: 999999.4 10-6 mol/mol Component Amount fraction Standard Assumed 10-6 mol/mol Uncertainty distribution Nitrogen 0.036 0.021 Rectangle Argon 0.021 0.012 Rectangle Carbon monoxide 0.0078 0.0045 Rectangle Carbon dioxide 0.092 0.00074 Normal Methane 0.0022 0.0013 Rectangle 19

Nitrous oxide 0.00049 0.00028 Rectangle Water 0.44 0.25 Rectangle Oxygen 999999.4 0.25 Normal Gravimetric Preparation Data We prepared 99 Oxygen gas by three steps dilution of pure oxygen gas by pure nitrogen gas with the gravimetric method based on ISO6142. In the first dilution, we prepared 46463.9 oxygen gas (Gas A), which was diluted to 2155 (Gas B) in the next step. In the final step, we prepared 99 (Gas C) by diluting the Gas B. Specification of Balance (Model No., Readability, Resolution, etc.,) Model No. : Mettler-Toledo Model: KA10-3/P Resolution : 1 mg Pooled experimental standard deviation for weighing, s p =3.9 mg, Weighing method (A-B-A, Substitution method, etc.,) A-B-B-A method was used. A and B corresponds to a reference and a sample cylinders, respectively. The sample and reference cylinders were 10 L Aluminum cylinders. The scheme A-B-B-A was automatically repeated 6 times per 1 measurement. The difference of readings between the reference and sample cylinders was always kept within ±1 g by using calibrated standard mass pieces (OIML E 2 class), which were traceable to the National Standards at NMIJ s mass force standard group. Coverage factor: 2, because of ISO6142. 20

In preparation of 46400 oxygen gas (Gas A) Weight of oxygen source gas: 55387.6 mg Weight of nitrogen source gas: 995096.4 mg Uncertainty source Mass of nitrogen gas (mg) Mass of Oxygen gas (mg) Molar mass of N 2 (mg/mol) Molar mass of O 2 (mg/mol) Purity of nitrogen gas () Conc. of Oxygen in nitrogen gas () Conc. of nitrogen in Oxygen gas () Purity of Oxygen gas () Estimate, Assumed x i distribution Contribution to Standard Sensitivity standard uncertainty, coefficient uncertainty, u(x i ), c i u(y i ) 995096.4 Normal 3.0-0.045 0.13 55387.6 Normal 3.0 0.80 2.4 28013.4 Rectangle 0.23-1.6 0.37 31998.8 Rectangle 0.35 1.4 0.48 999999.5 Normal 0.25 0.044 0.011 0.0031 Normal 0.00013 1.0 0.00013 0.036 Rectangle 0.021-0.039 0.00081 999999.4 Normal 0.25 0.0022 0.00055 Other impuritires ca 0.5 in nitrogen and oxygen gas Amount fraction of oxygen: 46463.9 Coverage factor: 2 Expanded uncertainty: 4.9 Negligible the uncertainty for 21

In preparation of 2150 oxygen gas (Gas B) Weight of Gas A: 53818.8 mg Weight of nitrogen source gas: 1099326.9 mg Amount fraction of oxygen: 2155.0 Coverage factor: 2 Expanded uncertainty: 0.31 Uncertainty source Mass of nitrogen gas (mg) Mass of gas A (mg) Molar mass of N 2 (mg/mol) Molar mass of O 2 (mg/mol) Purity of nitrogen gas () Conc. of Oxygen in nitrogen gas () Conc. of nitrogen in Gas A () Conc. of Oxygen in Gas A() Other impuritires in nitrogen and A gas Estimate, x i Assumed Standard distributio uncertainty, n u(x i ) Sensitivity coefficient, c i Contribution to standard uncertainty, u(y i ) 1099326.9 Normal 3.0-0.0019 0.0056 53818.8 Normal 3.0 0.038 0.11 28013.4 Rectangle 0.23-0.0039 0.00089 31998.8 Rectangle 0.35 0.0034 0.0012 999999.5 Normal 0.25 0.0021 0.00052 0.0031 Normal 0.00013 0.96 0.00013 953535.6 Rectangle 2.5-0.0020 0.0050 46463.9 Normal 2.5 0.044 0.11 ca 0.5 Negligible for the uncertainty 22

In preparation of 99 oxygen gas (Gas C) (Cylinder Number: CPC00641) Weight of gas B: 51085.4 mg Weight of nitrogen source gas: 1064271.1 mg Amount fraction of oxygen: 98.675 Coverage factor: 2 Expanded uncertainty: 0.018 Uncertainty source Mass of nitrogen gas (mg) Mass of gas A (mg) Molar mass of N 2 (mg/mol) Molar mass of O 2 (mg/mol) Purity of nitrogen gas () Conc. of Oxygen in nitrogen gas () Conc. of nitrogen in Gas B () Conc. of Oxygen in Gas B () Other impuritires in nitrogen and B gas Estimate, x i Contribution to Assumed Standard Sensitivity standard distributio uncertain coefficient uncertainty, n ty, u(x i ), c i u(y i ) 1064271.1 Normal 3.0-0.000088 0.00026 51085.4 Normal 3.0 0.0018 0.0055 28013.4 Rectangle 0.23-0.0000019 0.0000083 31998.8 Rectangle 0.35 0.0000072 0.0000025 999999.5 Normal 0.25 0.000094 0.000024 0.0031 Normal 0.00013 0.95 0.00013 997844.6 Rectangle 0.29-0.000094 0.000028 2155.0 Normal 0.16 0.046 0.0072 ca 0.5 Negligible for the uncertainty 23

Report form Laboratory: NPL Cylinder Number: Step One - Preparation of pre-mixture Parent 1= Pure oxygen Amount fraction Uncertainty CH4 0.00000000500000 0.00000000300000 CO 0.00000000050000 0.00000000029000 CO2 0.00000005000000 0.00000002900000 C3H8 0.00000000500000 0.00000000290000 H2 0.00000005000000 0.00000002900000 H2O 0.00000010000000 0.00000006000000 N2 0.00005000000000 0.00005000000000 O2 0.99978535000000 0.00012269000000 Parent 2 = Metrology grade nitrogen Amount fraction Uncertainty Ar 0.00000100000000 0.00000100000000 CO 0.00000002500000 0.00000001000000 CO2 0.00000011000000 0.00000001000000 CxHy 0.00000005000000 0.00000003000000 H2O 0.00000050000000 0.00000029000000 N2 0.99997421500000 0.00001443000000 NO2 0.00000005000000 0.00000003000000 SO2 0.00000005000000 0.00000003000000 Masses Added Parent Mass Uncertainty 24

Pure oxygen 153.25 0.020000 Metrology grade nitrogen 1159.02 0.020000 Daughter=Pre-mixture Amount fraction Uncertainty CH4 0.00000000051880 0.00000000031128 CO 0.00000002245786 0.00000000896244 CO2 0.00000010377435 0.00000000945404 C3H8 0.00000000051880 0.00000000030091 H2 0.00000000518804 0.00000000300906 H2O 0.00000045849570 0.00000025998392 N2 0.89622131830732 0.00002239950415 O2 0.10373848795471 0.00001309697005 Ar 0.00000089623924 0.00000089623911 CxHy 0.00000004481196 0.00000002688718 NO2 0.00000004481196 0.00000002688718 SO2 0.00000004481196 0.00000002688718 Step Two (Preparation of final mixture) Parent1=Pre-mixture (as above) Amount fraction Uncertainty CH4 0.00000000051880 0.00000000031128 CO 0.00000002245786 0.00000000896244 CO2 0.00000010377435 0.00000000945404 C3H8 0.00000000051880 0.00000000030091 H2 0.00000000518804 0.00000000300906 H2O 0.00000045849570 0.00000025998392 N2 0.89622131830732 0.00002239950415 O2 0.10373848795471 0.00001309697005 Ar 0.00000089623924 0.00000089623911 CxHy 0.00000004481196 0.00000002688718 NO2 0.00000004481196 0.00000002688718 25

SO2 0.00000004481196 0.00000002688718 Parent2=BIPplus grade Nitrogen Amount fraction Uncertainty Ar 0.00000100000000 0.00000100000000 CO 0.00000002500000 0.00000001000000 CxHy 0.00000005000000 0.00000003000000 N2 0.99992586000000 0.00001443000000 CH4 0.00000007500000 0.00000000900000 Masses Added Parent Mass Uncertainty 1 Pre-mixture 1.24 0.001200 2 Nitrogen 1279.48 0.020000 Final mixture Amount fraction Uncertainty CH4 0.00000007492892 0.00000000899141 CO 0.00000002499757 0.00000000999046 CO2 0.00000000009904 0.00000000000902 C3H8 0.00000000000050 0.00000000000029 H2 0.00000000000495 0.00000000000287 H2O 0.00000000043756 0.00000000024811 N2 0.99982689086174 0.00001441513888 O2 0.00009900153446 0.00000009637619 Ar 0.00000099990098 0.00000099904603 CxHy 0.00000004999505 0.00000002997138 NO2 0.00000000004277 0.00000000002566 SO2 0.00000000004277 0.00000000002566 All uncertainties given above are expanded with k=2. 26

Final result = 99.002 +/- 0.096 (k=2) oxygen in nitrogen Expanded uncertainty = 0.097% (relative) 27

Report form Laboratory: Bundesanstalt fuer Materialforschung und pruefung (BAM) Cylinder Number: BAM 6047 Amount fraction of oxygen: 99,17 Balance gas Nitrogen Purity of nitrogen: 10-6 mol/mol Component Amount fraction 10-6 mol/mol Uncertainty O 2 0,18 15 %rel. Ar <0,5 (not determined) H 2 0 <0,5 (not determined) CO <0,1 (not determined) CO 2 <0,1 (not determined) KW <0,1 (not determined) Nitrogen 99,9999 2*10-4 %rel Purity of oxygen: 10-6 mol/mol Component Amount fraction 10-6 mol/mol Uncertainty N 2 0,18 15 %rel. Ar <1 (not determined) H 2 0 <0,5 (not determined) CO <0,1 (not determined) CO 2 <0,1 (not determined) KW <0,1 (not determined) 28

Oxygen 99,9999 2*10-4 %rel Gravimetric Preparation Data Specification of Balance (Model No., Readability, Resolution, etc.,) Voland HCE25, Weighing method (A-B-A, Substitution method, etc.,) : According to ISO 6142 using a two arm balance (difference weighing: Reference- and Calibration gas cylinder. 3 pre-mixtures were used. Weight of oxygen source gas: each circa 150 g Weight of nitrogen source gas: each circa 1600 g Amount fraction of oxygen: 99,17 Balance gas Nitrogen Coverage factor: 2 Expanded uncertainty: 0,1 (without the uncertainty arises from the verification process and stability 0,25 (included the uncertainty arises from the verification process and stability) 29

Preparation scheme: O 2 N 2 210,827 g 1651,775 g Pre mixture 1 / BAM-6062 100507 O 2 899493 N 2 181,098 g Pre mixture 2 / BAM-6014 9885 O 2 990115 N 2 1636,841 g 185,601 g Pre mixture 3 / BAM-6037 1012 O 2 1625,292 g 998988 N 2 182,778 g Final mixture BAM-6047 99,17 O 2 Bilance: N 2 + Impurities 1684,492 g 30

Uncertainty source Estimate Assumed x i distribution Standard uncertainty u(x i ) Sensitivity codfficient c i Contribution to standard uncertainty u(y i ) Balance (A) 6 mg n 6 mg 1 6 mg Handling of cylinder (B) 4 mg n 4 mg 1 4 mg Imputities in O 2 (B) 2*10-4 %rel rectangle - O 2 in N 2 (A) 0,03 rectangle 1 0,06 mg Impurities in 2*10-4 %rel rectangle - N 2 (B) Composition 3*10-4 %rel n 1 0,5 mg of the pre mixtures to 6*10-4 %rel to 0,1 mg Verification (A) 0,2 n 1 0,1 Stability (B) <0,1 rectangle 1 0,1 / 2 years (not verifiable) 31

Report form Laboratory: Centro Español de Metrología (CEM) Cylinder Number: 06343 Purity of nitrogen: GC (Quality) Component Uncertainty Amount fraction 10-6 10-6 mol/mol mol/mol (K=2) CO 0,50 0,58 CO 2 0,50 0,58 H 2 1,00 1,16 O 2 0,01 0,01 H 2 O 0,02 0,02 CH 4 0,10 0,12 Component Amount fraction 10-2 mol/mol Uncertainty 10-6 mol/mol (K=2) Nitrogen 99,9998 1,42 Purity of oxygen: Component Uncertainty Amount fraction 10-6 10-6 mol/mol mol/mol (K=2) CO 0,50 0,58 CO 2 0,50 0,58 H 2 1,50 1,73 N 2 4,00 4,62 H 2 O 1,50 1,73 HC 0,50 0,58 Component Amount fraction 10-2 mol/mol Uncertainty 10-6 mol/mol (K=2) Oxygen 99,9992 5,32 32

Gravimetric Preparation Data Specification of Balance (Model No., Readability, Resolution, etc.,) Mass comparator, Mettler Toledo PR10003, maximum range: 10100 g; repeatability: 2 mg; resolution: 1 mg; linearity: 10 mg; E2 masses are used. The cycle of weighing is as follows (two differents cases): If the weight of the reference is bigger than the weight of sample: 1.- Reference + 1 g 2.- Reference 3.- Sample + weights 4.- Reference 5.- Sample + weights 6.- Reference 7.- Sample + weights 8.- Reference 9.- Reference + 1 g If the weight of the reference is smaller than the weight of sample: 1.- Reference + 1 g + weights 2.- Reference + weights 3.- Sample 4.- Reference + weights 5.- Sample 6.- Reference + weights 7.- Sample 8.- Reference + weights 9.- Reference + 1 g + weights The weighing data are collected directly by software, with temperature, pressure and humidity values. 33

This software also collect the raw material data (O 2 and N 2 ) and with all those date the software calculates the uncertainty of the mixture following ISO 6142, but as it is calculated by the software, it is not possible to fill the table of each uncertainty contribution. Weight of oxygen source gas: 69,963 8 g Weight of nitrogen source gas: 628,334 6g Amount fraction of oxygen: 100,04 Coverage factor: k = 2 Expanded uncertainty: 0,023 34

Report form Laboratory: National Measurement Institute Australia (NMIA) Report for CCQM K53: Oxygen in Nitrogen Cylinder Number: ME2630 Source Gases: Purity of nitrogen: 999 996.9 10-6 mol/mol Component Amount fraction 10-6 mol/mol Uncertainty Oxygen 1.07 0.11 Water 1.5 1.7 Methane 0.50 0.58 Nitrogen 999 996.9 1.7 Purity of oxygen: 999 994.4 10-6 mol/mol Component Amount fraction 10-6 mol/mol Uncertainty Argon 1.5 1.7 Nitrogen 2.5 2.9 Water 1.5 1.7 Methane 0.1 0.1 Oxygen 999 994.4 3.8 Gravimetric Preparation Data Specification of Balance (Model No., Readability, Resolution, etc.,) Mass Comparator: Sartorius CC10000S. Resolution 0.1mg. Readability 0.1mg Reproducibility 0.25mg Uncertainty of 0.5mg 35

Weighing method (A-B-A, Substitution method, etc.,) An ABBA weighing scheme is used to minimise the effect of instrument and environmental drift. This involves weighing a reference mass (cylinder) prior to and after two weighings of the sample mass. During the weighing process, the air temperature, pressure and relative humidity are measured during each reading on the mass comparator to calculate the air density. The air density is used to correct for changes in the buoyancy of cylinders and rings. Dilution Stages: First stage dilution (cylinder ME2635): Mass of oxygen source gas: 10.5794 g Mass of nitrogen source gas: 175.3509 g Amount fraction of oxygen: 50.169 mmol/mol Coverage factor: 2 Expanded uncertainty: 0.029 mmol/mol Second stage dilution (cylinder ME2633): Mass of oxygen source gas: 10.2033 g Mass of nitrogen source gas: 192.9448 g Amount fraction of oxygen: 2.5029 mmol/mol Coverage factor: 2 Expanded uncertainty: 0.0021 mmol/mol Final Stage dilution (cylinder ME2630): Mass of oxygen source gas: 20.4491 g Mass of nitrogen source gas: 495.9964 g Amount fraction of oxygen: 100.10 Coverage factor: 2 Expanded uncertainty: 0.14 36

37

Report form Laboratory: NIST Cylinder Number: CAL016875 Purity of nitrogen: 10-6 mol/mol Component Amount fraction 10-6 mol/mol Uncertainty Oxygen 0.005 0.005 Argon 1 1 Water 4 4 CO2 0.03 0.03 Nitrogen 999995 5 Purity of oxygen: 10-6 mol/mol Component Amount fraction 10-6 mol/mol Uncertainty Nitrogen 10 10 Argon 5 5 CO 0.02 0.02 CO2 0.1 0.1 Water 4 4 Oxygen 999981 19 38

Gravimetric Preparation Data Specification of Balance (Model No., Readability, Resolution, etc.,) 1) Mettler B5C1000, Readability 0.1 mg, Capacity 1000 g, uncert (k=1) 0.2 mg 2) Voland HCE 10, Readability 1 mg, Capacity 15 Kg, uncert (k= 1) 9 mg 3) Mettler Readability 0.01 g, Capacity 10.1 Kg, uncert 0.03 g Weighing method (A-B-A, Substitution method, etc.,) Substitution method, reference cylinder (A-B-A) Mixture 1: Weight of oxygen source gas: 0.44419 g Weight of nitrogen source gas: 384.618 g Amount fraction of oxygen: 1010.0 Coverage factor: 2 Expanded uncertainty: 1.1 Uncertainty source Estimate Assumed x i Distribution Standard uncertainty u(x i ) Sensitivity coefficient c i Contribution to standard uncertainty u(y i ) Mass Parent Gas 0.44419 normal 0.00024 2070 0.504 Mass Balance Gas 384.618 normal 0.018 0.11 0.0021 MW O2 31.9988 normal 0.0004 0.4 0.00016 MW N2 28.0134 normal 0.0003 0.3 0.00009 Impurities in balance 69 µmol Rectangular 57 µmol 0.3 0.00002 Impurities in oxygen 0.13 µmol Rectangular 0.09 µmol 4 3.6 x 10-7 Mass O2 from N2 2.2 µg Rectangular 2.2 µg 105 0.00023 Mass N2 from O2 3.9 µg Rectangular 3.9 µg 0.09 3.6 x 10-7 39

Mixture 2: Weight of oxygen gas: 0.0974858 g Weight of nitrogen source gas: 849.824 g Amount fraction of oxygen: 100.41 Coverage factor: 2 Expanded uncertainty: 0.12 Uncertainty source Estimate Assumed x i Distribution Standard uncertainty u(x i ) Sensitivity coefficient c i Contribution to standard uncertainty u(y i ) Mass O2 from Parent Gas 0.0974858 Normal 0.000056 980 0.055 Mass N2 from Balance Gas 765.416 Normal 0.015 0.0018 0.000026 Mass N2 from Parent 84.407 Normal 0.013 0.0015 0.000020 Total N2 added 849.824 Normal 0.020 0.0023 0.000046 MW O2 31.9988 Normal 0.0004 0.035 0.000015 MW N2 28.0134 Normal 0.0003 0.032 0.000009 Impurities in Balance 470 µmol Rectangular 12 µmol 0.0012 1.4 x 10-8 Impurities in Oxygen 3.9 µmol Rectangular 3.1 µmol 0.0004 1.3 x 10-9 Mass O2 from N2 4.4 µg Rectangular 4.4 µg 41 0.00018 40

Report form Laboratory: NMISA Cylinder Number: 8396 Purity of nitrogen: 999999,375 x 10-6 mol.mol -1 Component Amount fraction x 10-6 mol.mol -1 CO 0,0215 0,0248 CO 2 0,050 0,019 H 2 0,5 0,58 H 2 O 0,01 0,012 HC (Hydrocarbons) 0,05 0,058 O 2 0,005 0,0058 Nitrogen 999999,375 0,822 Uncertainty (k=2) Purity of oxygen: 999975,75 x 10-6 mol.mol -1 Component Amount fraction x 10-6 mol.mol -1 CO 0,25 0,29 CO 2 0,5 0,58 H 2 O 1,5 1,73 HC (Hydrocarbons) 0,25 0,29 N 2 21,77 3,31 Oxygen 999975,75 5,377 Uncertainty (k=2) Gravimetric Preparation Data Specification of Balance (Model No., Readability, Resolution, etc.,) Mettler Toledo PR 10003, Readability: 0,01 mg, Resolution: 0,01 mg Weighing method (A-B-A, Substitution method, etc.,) Substitution method Weight of oxygen source gas: 67,51552 g 41

Weight of nitrogen source gas: 608,84153 g Amount fraction of oxygen: 100,585 x 10-6 mol.mol -1 Coverage factor: 2 Expanded uncertainty: 0,022 x 10-6 mol.mol -1 1. Preparation Data - Weights of nitrogen and oxygen in the dilution series First dilution step: 10% mol.mol -1 Component Weight (g) Combined Standard uncertainty (mg) O 2 77,65790 2,93 N 2 611,33409 4,78 Second dilution step: 1% mol.mol -1 Component Weight (g) Combined Standard uncertainty (mg) O 2 68,21527 2,42 N 2 604,85897 4,55 Third dilution step: 1000 x 10-6 mol mol -1 Component Weight (g) Combined Standard uncertainty (mg) O 2 68,57319 2,55 N 2 612,14684 4,70 Final dilution step: 100 x 10-6 mol mol -1 Component Weight (g) Combined Standard uncertainty (mg) O 2 67,51552 2,15 N 2 608,84153 4,11 42

2. Example of uncertainty sources in gravimetric preparation Weighing data for 100 x 10-6 mol mol -1 mixture i. Vacuum weighing Standard Uncertainty Type Degrees uncertainty Sensitivity contribution (c x A/B of Parameter Estimate (u) coefficient (c) u) freedom Sensitivity 0,998916176 0,000355035 0,9024550000 0,000320403 A 1 Weighing difference 0,9024550000 0,0027276946 0,998916176 0,002724738 A 2 Mass pieces 94,9998700000 0,0000342783 0,999870954 3,42738 x 10-5 B infinity Air density 1,032370366 0,00018131 0 0 B infinity Volume expansion 0,011874984 5,52548 x 10-6 1,0323703657 5,70434 x 10-6 B infinity Density of mass pieces (stainless B steel) 8000 0,002-1,53242 x 10-6 -3,06485 x 10-9 infinity Mass (g) 95,9013469 Standard uncertainty (mg) 2,743731814 ii. Weighing after oxygen addition Uncertainty Type Degrees Standard Sensitivity contribution (c A/B of Parameter Estimate uncertainty (u) coefficient (c) x u) freedom Sensitivity 0,999020959 0,001580008 0,4348850000 0,000687122 A 1 Weighing difference 0,4348850000 0,0019959222 0,999020959 0,001993968 A 2 Mass pieces 162,9997800000 0,0000572276 0,999871545 5,72203 x 10-5 B infinity Air density 1,027639609 0,000224203 0 0 B infinity Volume expansion 0,020374973 9,25559 x 10-6 1,0276396094 9,51141 x 10-6 B infinity Density of mass pieces (stainless B steel) 8000 0,002-2,61727 x 10-6 -5,23453 x 10-9 infinity Mass (g) 163,4342392 43

Standard uncertainty (mg) 2,109836412 iii. Weighing after nitrogen addition Standard Uncertainty Type uncertainty Sensitivity contribution (c x A/B Degrees of Parameter Estimate (u) coefficient (c) u) freedom Sensitivity 0,99903593 0,002765005 0,3176808333 0,000878389 A 1 Weigh difference 0,3176808333 0,0024916257 0,99903593 0,002489224 A 2 Mass pieces 771,9997900000 0,0002710166 0,999871204 0,000270982 B infinity Air density 1,030366305 0,000219835-0,093499974-2,05545 x 10-5 B infinity Volume expansion 0,015 0,003 1,0303663047 0,003091099 B infinity Density of the B mass pieces (stainless steel) 8000 0.002-1,24288 x 10-5 -2,48576 x 10-8 infinity Mass (g) 772,2331897 Standard uncertainty (mg) 4,073885998 iv. Purity table of 100 x 10-6 mol.mol -1 mixture Component Amount fraction Standard uncertainty Expanded uncertainty (x10-6 ) mol.mol -1 (x10-6 ) mol.mol -1 (x10-6 ) mol.mol -1 CO 0,0215229837321941 0,0112181047460089 0,0224362094920178 CO 2 0,0500452626747415 0,0085945576033417 0,0171891152066834 H 2 0,499949708966935 0,2611599738496610 0,522319947699323 H 2 O 0,0101498670550384 0,0052239257597787 0,0104478515195573 HC (Hydrocarbons) 0,0500201171582091 0,0261160014201652 0,0522320028403305 N 2 999898,795186808 12,7353886912900000 25,4707773825799 O 2 100,584626511606 0,0112353386373686 0,0224706772747372 44

Coverage factor : 2 ; level of confidence = 95,45% ; ν = Expanded uncertainty : 0,02247 (x10-6 ) mol.mol -1 eff 45

Report form Laboratory: CENAM Cylinder Number: FF39563 Purity of nitrogen: 999998,84 10-6 mol/mol Component Amount fraction 10-6 mol/mol Uncertainty O 2 0,15 0,10 CO 0,11 0,08 CO 2 0,30 0,13 CH 4 0,100 0,058 H 2 O 0,50 0,31 Nitrogen 999998,84 0,19 Purity of oxygen: 999989,77 10-6 mol/mol Component Amount fraction 10-6 mol/mol Uncertainty N 2 0,54 0,15 CO 1,0 0,58 CO 2 1,0 0,58 CH 4 0,292 0,086 H 2 O 4,90 2,80 Ar 0,243 0,046 THC 0,1 0,058 H2 0,1 0,058 Kr 1,0 0,58 Xe 1,0 0,58 He 0,1 0,058 Oxygen 999989,77 3,04 46

Gravimetric Preparation Data The preparation of the standard gas mixture was carried by at least three steps dilution as show in the diagram: O 2 N 2 O 2 N 2 1 2 1 2 Mezcla 1,5 cmol/mol O 2 /N 2 1 2 2 N 2 Mezcla 1,5 cmol/mol O 2 /N 2 1 Mezcla 800 Mezcla 1000 2 Mezcla 1200 O 2 /N 2 O 2 /N 2 O 2 /N 2 1 1 1 2 2 2 2 2 2 N 2 Mezcla 80 O2/N2 Mezcla 90 O2/N2 Mezcla 101 O2/N2 Mezcla 110 O2/N2 Mezcla 101 O2/N2 Mezcla 120 O2/N2 Preparation of the cylinders before the filling The used cylinders to prepare the mixtures are aluminum made type ALS, they were provided by the Praxair Mexico (manufacturer LUXFER). Praxair Mexico carry out routine tests on the cylinders: Vent hydrostatic pressure, leaks, humidity analysis, passivation, vacuum level, and cleaning. Before weighing each cylinder The external surface and valve of each cylinder was cleaned using a cotton cloth with alcohol to eliminate dust or remainders of the cylinder. It was carried out a vacuum to each cylinder < 0,7 Pa, using the filling panel of the gas mixture preparation system. The cylinders with low pressure and cleaned were introduce to the gas mixture preparation lab to let acclimate to reach the laboratory temperature (24 h). Filling of the mixtures Previous to the filling it was come to weigh the clean cylinders, selecting as a reference cylinder the one that had similar weight. Later was made the filling in agreement with CENAM internal procedures. Determination of mass by means of weight 47

The calibration standards for the measurements were primary standards (primary standard mixtures, PSMs), prepared by weigh, the cylinders were weighted after each compound addition and thermal equilibrium with the room. The method used for the preparation of PSMs was the gravimetric method following the guidelines of the ISO/DIS 6142. The procedure for weighing was a Borda weighing scheme (RTRTRTR). CENAM experts prepared the gas mixtures at the gas producer facilities (Praxair). Specification of Balance The instrument for weighing was a Mettler balance model KB-50 (60 kg capacity and 0,05 g resolution) and sets of weights class E2 (serial number 520779750101, from 1 to 5 kg 4 pieces) and E2 (serial number 41003979, from 1 mg to 1 kg 25 pieces) according to the R 111 of OIML, all of them traceable to SI by CENAM s Standards. Weight of oxygen source gas: 95,90 g Weight of nitrogen source gas: 854,01 g Amount fraction of oxygen: 100,97 Coverage factor: k = 2 *Expanded uncertainty: 0,30 *Expanded uncertainty: It was obtained by the product of the combined standard uncertainty and a coverage factor of 2 at 95% level of confidence Uncertainty budget submitted of the gas mixture. The uncertainty of the standard mixture has been calculated applying the law of propagation of uncertainties to the equation 3 of the ISO 6142 (2001). The uncertainty contributions taken in account are following: A.- The uncertainty in molar mass B.- The uncertainty on the weighing C.- The uncertainty in the purity analysis. A. The uncertainty of molar masses has been taken as a type B evaluation of uncertainty from the IUPAC assuming a uniform distribution. B. The uncertainty of weighing has been calculated using the law of propagation of 48

uncertainties to the model for single substitution weighing: m T = m R + ρ a * (V T - V R ) + Ιω / S where: m T = mass of the tested cylinder m R = reference mass ρ a = air density V T = weights used in the tested cylinder V R = weights used in the reference cylinder Ιω = difference in balance readouts S = balance sensitivity C. The uncertainty in the purity analysis. Their uncertainties were calculated by type A evaluation or/and type B evaluation. Uncertainty budget mixture 49

Uncertainty source Estimate Standard uncertainty Assumed Distribution Sensitivity coefficient Contribution to standard uncertainty X I x I u(x i ) C I u I (y) MH2O 18.01528 0.00009 Rectangular -9.02E-13 6.77E-33 MN2 28.01348 0.00003 Rectangular 3.70E-09 1.12E-26 MTHC 44.04180 0.00147 Rectangular -1.62E-12 5.67E-30 MH2 2.01588 0.00003 Rectangular -3.23E-16 8.53E-41 MCO 28.01010 0.00025 Rectangular -5.75E-13 2.01E-32 MCO2 44.00950 0.00026 Rectangular -1.52E-12 1.58E-31 MAr 39.94800 0.00029 Rectangular -7.85E-16 5.14E-38 MCH4 16.04246 0.00023 Rectangular 3.23E-13 5.72E-33 MKr 83.8000 0.0029 Rectangular -3.23E-15 8.71E-35 MXe 131.2900 0.0058 Rectangular -3.23E-15 3.48E-34 MHe 4.002602 0.000001 Rectangular -3.23E-16 3.48E-44 MO2 31.99880 0.00012 Rectangular -3.23E-09 1.57E-25 mo2 95.899 0.055 Normal 9.45E-07 2.70E-15 mn2 854.093 0.061 Normal -1.06E-07 4.13E-17 XH2O,O2 0.775 0.031 Normal -5.83E-05 3.21E-24 XN2,O2 998998.63 1.32 Normal -9.06E-05 1.43E-20 XTHC,O2 0.50 0.14 Rectangular -1.42E-04 3.70E-22 XH2,O2 0.000100 0.000029 Rectangular -6.52E-06 3.54E-32 XCO,O2 0.290 0.073 Rectangular -9.06E-05 4.35E-23 XCO2,O2 0.768 0.026 Rectangular -1.42E-04 1.35E-23 XAr,O2 0.000243 0.000023 Normal -1.29E-04 8.70E-30 XCH4,O2 0.000292 0.000043 Normal -5.19E-05 5.01E-30 XKr,O2 0.00100 0.00029 Rectangular -2.71E-04 6.11E-27 XXe,O2 0.00100 0.00029 Rectangular -4.25E-04 1.50E-26 XHe,O2 0.000100 0.000029 Rectangular -1.29E-05 1.39E-31 XO2,O2 999.04 1.28 Rectangular 0.100830805 1.68E-14 XO2,N2 0.153 0.056 Normal 0.89916921 2.54E-15 XH2O,N2 0.50 0.16 Normal 5.83E-05 8.38E-23 XCO,N2 0.112 0.039 Normal 9.06E-05 1.23E-23 XCO2,N2 0.299 0.064 Normal 1.42E-04 8.30E-23 XCH4,N2 0.100 0.029 Rectangular 5.19E-05 2.25E-24 XN2,N2 999998.84 0.19 Rectangular 9.06E-05 2.81E-22 CENAM Participants List: Francisco Rangel Murillo, Victor M. Serrano Caballero, Alejandro Pérez Castorena 50

Report form Laboratory: LNE Cylinder Number: 1022352 Purity of nitrogen: 0.999999885 mol/mol Component Amount fraction 10-6 mol/mol Uncertainty O 2 0.0050 0.0029 H 2 O 0.0100 0.0058 CO+CO 2 0.025 0.014 THC 0.050 0.029 H 2 0.025 0.014 Nitrogen 0.999999885 0.000000036 Purity of oxygen: 0.999998675 mol/mol Component Amount fraction 10-6 mol/mol Uncertainty H 2 O 0.500 0.025 N 2 0.800 0.050 C n H m 0.0050 0.0029 CO 2 0.0050 0.0029 H 2 0.0050 0.0029 CO 0.0050 0.0029 NO x 0.0050 0.0015 Oxygen 0.999998675 0.000000057 51

Gravimetric Preparation Data Specification of Balance (Model No., Readability, Resolution, etc.,) Mettler balance : - ID5 15kg at 2 mg/ PR2004 2300 g at 0.1 mg Weighing method (A-B-A, Substitution method, etc.,) -weighing empty small cylinder + standards mass (10 weighing) -weighing small cylinder with parent mixture (10 weighing) -weighing empty cylinder + standards mass (10 weighing) -weighing cylinder with parent mixture + nitrogen (10 weighing) Amount fraction of oxygen: 101.04 Coverage factor: 2 Expanded uncertainty: 0.10 Uncertainty source Weight of small cylinder with O2/N2 Weight of empty small cylinder with standard weight Weight of cylinder with O2/N2 and N2 Weight of cylinder with standard weight Estimate Assumed x i distribution Standard uncertainty u(x i ) Sensitivity codfficient c i Contribution to standard uncertainty % 1300.93936 σ(exp) 9.9 10-4 30 69.7 1301.5445 σ(exp) 5.1 10-4 -30 18.3 15434.5938 σ(exp) 6.8 10-3 -6.7 10-2 0.02 15624.2538 σ(exp) 6.1 10-3 6.7 10-2 0.01 N2 molar mass 28.01348 U=ku 8.5 10-5 1.85 10-1 - O2 molar mass 31.9988 U=ku 4.2 10-4 -1.62 10-1 - N2 purity 0.999999885 U=ku 3.6 10-8 -100 - Standard weight 1699.99987 U=ku 2.85 10-4 -6.7 10-2 - Amount fraction 45242 10-2 U=ku 5.5 10-6 2219 11.9 Standard weight 3.999964 U=ku 2.85 10-5 29.8 0.06 Air density 1.194236 U=ku 2.33 10-3 -1.3 10-2 - Air density 1.191798 U=ku 2.33 10-3 1.26 10-2 - Resolution balance 1 0 uniform 5.8 10-5 -7 10-10 - Resolution balance 2 0 uniform 5.8 10-3 -2.1 10-13 - 52

CCQM-K53 (Oxygen in Nitrogen) Report form Date: 16 Dec 2006 Laboratory: Korean Research Institute of Standards and Science (KRISS) Prepared 101 oxygen gas Cylinder Number: ME5697 Amount fraction of oxygen: 101.053 Coverage factor: 2 Expanded uncertainty: 0.020 Results of determinations Nitrogen source gas: 99.99932 %mol/mol Component Amount fraction (10-6 mol/mol) Standard uncertainty (10-6 mol/mol) Assumed distribution Hydrogen 0.05 0.0289 Rectangular Oxygen 0.0007 0.00007 Normal Carbon monoxide 0.007 0.0014 Normal Carbon dioxide 0.0025 0.0014 Rectangular Methane 0.009 0.0018 Normal Argon 2.4 0.24 Normal Water 0.25 0.075 Normal Nitrous oxide 0.0001 0.00006 Rectangular Hydrocarbons(CxHy) 0.025 0.01443 Rectangular Neon 4.1 0.82 Normal Nitrogen 999993.2 0.253 Normal 53

Oxygen source gas: 99.99978 %mol/mol Component Amount fraction (10-6 mol/mol) Standard uncertainty (10-6 mol/mol) Assumed distribution Hydrogen 0.05 0.0289 Rectangular Nitrogen 0.73 0.146 Normal Carbon monoxide 0.02 0.004 Normal Carbon dioxide 0.2 0.02 Normal Methane 0.005 0.0029 Rectangular Argon 0.05 0.0289 Rectangular Water 1.1 0.33 Normal Oxygen 999997.8 0.364 Normal Gravimetric Preparation Data Primary standard gas mixture was prepared gravimetrically through three steps dilution according to ISO6142. Specification of Balance (Model No., Readability, Resolution, etc.,) Model No. : Mettler-Toledo Resolution : 1 mg, Capacity : 10 Kg Uncertainty (k=2) : 3.2 mg Weighing method (A-B-A, Substitution method, etc.,) Substitution method, tare cylinder (A-B-A) Fig. 1 shows the diagram where the preparation of the standard gas mixture was carried by at least three steps of dilution. 54

Pure N2 Pure O2 YA001678 YA001682 YA001916 Pure N2 Pure N2 YA002044 YA002030 YA001768 Pure N2 Pure N2 ME5662 ME5704 ME5697 ME5648 Figure 3 Diagram of the preparation of the standard gas mixture Preparation of 4 % mol/mol oxygen in nitrogen (Parent gas A) Weight of oxygen source gas : 50.0110 g Weight of nitrogen source gas : 1102.6037 g Amount fraction of oxygen : 3.819179 %mol/mol Coverage factor : 2 Expanded uncertainty : 2.80 Uncertainty source Estimate Standard uncertainty Assumed distribution Sensitivity coefficient Contribution to standard uncertainty Mass of O 2 (g) 50.0110 0.00115 Normal 73 0.85 Mass of N 2 (g) 1102.6037 0.00203 Normal -3.3-0.068 Purity of pure O 2 gas (mol/mol) Purity of pure N 2 gas (mol/mol) Impurity of O 2 in N 2 gas () Atomic weight of O (g/mol) 0.9999978 0.000000360 Normal 3.7 0.013-0.00930 0.9999932 0.000000253 Normal -3.7 0.000067 0.00070 0.00007 Normal 0.96 15.999400 0.000150 Normal -0.23-0.34 55

Atomic weight of N (g/mol) Uncertainty of balance(mg) 14.006740 0.000035 Normal 0.26 0.092 0.0 1.51 Normal 0.000070 1.10 Preparation of 0.2 %mol/mol oxygen in nitrogen (Parent gas B) Weight of parent gas A : 57.56133 g Weight of nitrogen gas : 1083.07600 g Amount fraction of oxygen : 0.191743 %mol/mol Coverage factor : 2 Expanded uncertainty : 0.222 Uncertainty source Mass of parent gas A (mg) Mass of N 2 diluent gas (mg) Conc. of O 2 in parent gas A (%mol/mol) Conc. of N 2 in parent gas A (%mol/mol) Purity of pure N 2 gas (mol/mol) Impurity of O 2 in pure N 2 gas () Impurity of pure O 2 gas () Estimate Standard Assumed Sensitivity Contribution to uncertainty distribution coefficient standard uncertainty 57.5613 0.000667 Normal 3.2 0.021 1083.0760 0.00153 Normal -0.17-0.0026 3.819153 0.000141 Normal 0.048 0.068 96.180187 2.30 Normal -0.0019-0.0044-0.00046 0.9999932 0.000000253 Normal -0.18 0.00007 0.00070 0.00007 Normal 1.0-0.0.00000230 2.200 0.635 Rectangular -0.0000000004 Impurity of pure N 2-0.00380 gas except O 2 6.80 1.96 Rectangular -0.000000190 () Molecular weight 31.998800 0.000300 Normal -0.000250-0.00074 56

of O 2 (g/mol) Molecular weight -0.00020 28.013480 0.000070 Normal 0.000280 of N 2 (g/mol) Uncertainty of 0.0 1.51 Normal 0.0000030 0.045 balance (mg) Preparation of 101 oxygen in nitrogen (Standard gas) Weight of parent gas B : 33.8010 g Weight of nitrogen gas : 607.3820 g Amount fraction of oxygen : 101.053 Coverage factor : 2 Expanded uncertainty : 0.015 Standard Assumed Sensitivity Contribution to Uncertainty source Estimate uncertainty distribution coefficient standard uncertainty Mass of parent gas 0.00160 33.8010 0.000577 Normal 0.28 B(g) Mass of N 2-0.000091 607.3820 0.000577 Normal -0.016 diluent gas (g) Conc. of O 2 in 0.00580 parent gas B 0.1917425 0.0000111 Normal 0.053 (%mol/mol) Conc. of N 2 in -0.00020 parent gas B 99.807579 0.0001963 Normal -0.0001 (%mol/mol) Purity of pure N 2-0.000024 0.9999932 0.000000253 Normal -0.0096 gas (mol/mol) Conc. of O 2 in 0.00007 pure N 2 gas 0.00070 0.00007 Normal 1.0 () Impurity of pure -0.00000000650 2.200 0.635 Rectangular -0.000000000001 O 2 gas () Impurity of pure -0.00020 N 2 gas except O 2 6.80 1.96 Rectangular -0.00000001 () Molecular weight 31.998800 0.000300 Normal -0.000000660-0.00000200 57

of O 2 (g/mol) Molecular weight of N 2 (g/mol) Uncertainty of balance (mg) 28.013480 0.000070 Normal 0.000000750 0.0 1.51 Normal 0.000000270 0.00000052 0.00400 58

Key Comparison CCQM-K53 Oxygen in Nitrogen Report 29.09.06 Laboratory: VNIIM, Research Department for the State Measurement Standards in the field of Physico-Chemical Measurements Cylinder Number: D717220 Purity of nitrogen: 999993,2 10-6 mol/mol Component Standard Amount fraction 10-6 uncertainty mol/mol 10-6 mol/mol Hydrogen 0,05 0,006 Oxygen 0,37 0,023 Argon 2,8 0,12 Water 2,0 0,12 Carbon dioxide 1,1 0,17 Carbon monoxide 0,25 (< 0,5) 0,14 Methane 0,25 (< 0,5) 0,14 Nitrogen 999993,2 0,3 Purity of oxygen: 999989,2 10-6 mol/mol Component Standard Amount fraction 10-6 uncertainty mol/mol 10-6 mol/mol Hydrogen 0,015 0,0052 Argon 1,0 0,06 Nitrogen 4,2 0,35 Krypton 0,06 0,006 Methane 1,2 0,06 Carbon dioxide 0,5 (< 1) 0,17 Xenon 0,005 (< 0,01) 0,0029 59

Water 3,8 0,23 Oxygen 999989,2 0,5 Gravimetric Preparation Data Specification of Balance Model: 81-V-HCE-20kg, hnu-voland, USA; Readability: 1 mg; Experimental standard deviation for 10 l cylinder: 5,7 mg. Weighing method - Substitution method. Weight of oxygen source gas: 0,13259 g Weight of nitrogen source gas: 1144,002 g (Preparation of the gas mixture was carried out in 2 stages. Amount fraction of oxygen in the pre-mixture X=0,994211 mol. %; u(x)=0,000435 mol. %) Amount fraction of oxygen: 101,08 Coverage factor: 2 Expanded uncertainty: 0,14 Uncertainty source Assume Standard Estimate d uncertain x i distributi ty on u(x i ) Contribution Sensitivity to standard coefficient uncertainty c i u(y i ), m O2 Preparation 12,908 g Normal 5,7 mg 7,703 10-3 0,0439 of the premixture Preparation of the final m N2 m pre-mixture 1125,392 g 5,7 mg 8,835 10-5 0,0005 Normal 11,590 g Normal 5,7 mg 8,589 10-3 0,0490 mixture m N2 1132,543 g Normal 5,7 mg 1,579 10-4 0,0009 Purity of O 2 in N 2 0,37 0,023 1 0,023 gases Normal 60

Other impurities 6,45 Normal - - 0,00001 Molar masses Combined uncertainty in N 2 Impurities 10,8 in O 2 standard are not taken into account Normal - - 0,00004 0,0697 61

Report form Laboratory: VSL Cylinder Number: D751963 Purity tables pure gases: 62

Gravimetric Preparation Data Specification of Balance (Model No., Readability, Resolution, etc.,) Sartorius 10 kg comparator scale, repeatability 1 mg. Use pooled estimate for 63