Comparison APMP.QM-S2.1, Oxygen in nitrogen at atmospheric ...

1

APMP.QM-S2.1 report

Comparison APMP.QM-S2.1

Oxygen in nitrogen at atmospheric level

Final Report

ByungMoon Kim1, Kwangsub Kim

1, Jinsang Jung

1,*, Sanghyub Oh

1, Liu Hui

2, Hou Li

2, Teo

Beng Keat2, Chua Hock Ann

2

1Korea Research Institute of Standards and Science (KRISS), Center for Gas Analysis, 267

Gajeong-ro, Yuseong-Gu, Daejeon 305-340, Republic of Korea 2National Metrology Centre, A*STAR, #02-27 TUV SUD PSB building, 1 Science Park Drive,

118221, Singapore

*Corresponding to Jinsang Jung: [email protected]

Field Amount of substance

Subject Comparison of 0.2 mol/mol oxygen in nitrogen

Participants KRISS(Korea), NMC/A*STAR(Singapore)

Organizing body APMP

Table of contents

Introduction……………………………………………………………………………………....3

Supported CMC claims…………………………………………………………………………...3

Schedule…………………………………………………………………………..…….………...3

Process of the comparison………………………………………………………………………..4

Measurement protocol………………………………………………………………………..…..5

Measurement methods…………………………………………………………………………....5

mailto:[email protected]

2

Degrees of equivalence…………………………………………………………………………...6

Result………………………………………………………………………….………….……....7

Conclusion………………………………………………………………………….……….…....9

Appendix A. Verification of mixtures with GC-TCD………………………………….………..10

Appendix B. Report from each laboratory……………………………………………….………13

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Introduction

NMC/A*STAR has a schedule to start the calibration service of oxygen in nitrogen gas mixtures

near atmospheric concentration in recent years. NMC/A*STAR is required to show its

competence in measurement and calibration of oxygen at these concentration levels. KRISS and

NMC/A*STAR agreed to collaborate in the area of gas metrology. KRISS organize a bilateral

comparison between KRISS and NMC/A*STAR to show the comparability between them. This

comparison was suggested and approved in the meetings of APMP TCQM in November 2013

and CCQM GAWG in April 2014.

This document describes results of the bilateral comparison of an oxygen in nitrogen gas

mixture. The nominal amount-of-substance fraction was 0.2 mol/mol oxygen in nitrogen.

Supported CMC claims

This comparison can be used to support CMC claims for oxygen in nitrogen matrix from 0.05

mol/mol to 0.3 mol/mol if same impurity analysis and uncertainty evaluation are performed

based on participants’ reports.

Schedule

November 2013 Protocol issued by KRISS

January 2014 Preparation of mixtures and first verification measurement

April 2014 Shipment of sample cylinder to participating laboratory

(NMC/A*STAR)

31 July 2014 Submission of measurement report to KRISS

September 2014 Return of the sample cylinder to KRISS

March 2015 Second verification measurement

April 2015 Draft A report

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April 2015 Draft B report

August 2015 Draft B APMP TCQM review

October 2015 Draft B CCQM GAWG review

October 2015 Final approved

Process of the comparison

A set of mixtures of oxygen in nitrogen with nominal fractional amounts of 0.2 mol/mol was

prepared gravimetrically according to ISO 6142 [1]. The mixtures were verified against primary

reference mixtures. The pressure in the cylinders was approximately 100 bar and Luxfer

cylinders of 10 dm3 nominal were used. The amount-of-substance fractions were derived from

gravimetry, molar mass, and purity verification of the parent gases. The gravimetric values were

used as the Key Comparison Reference Values (KCRVs). Thus, each cylinder has its own

reference value.

The participating laboratory was requested to specify in detail which analytical method(s) were

used and how the measurement uncertainty was evaluated. The participating laboratory was

responsible for the calibration of its own equipment. For a proper evaluation of the data, it was

necessary that the calibration method, as well as the way in which the calibration mixtures were

prepared, were reported to the coordinating laboratory.

The laboratory was asked to express the uncertainty on all results withthe evaluation of

measurement uncertainty in accordance with the “Guide to the express of uncertainty in

measurement” (ISO GUM). The participant was asked to provide a detailed description of the

uncertainty budget, including:

- method of evaluation (type A or B)

- (assumed) probability distribution

- standard uncertainties and sensitivity coefficients

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After the measurement, the participating laboratory was requested to return the cylinder with

sufficient amount of the gas (pressure at least 30 bar) to the coordinating laboratory for re-

analysis.

The cylinder was shipped to the participant in April 2014. The participating laboratory carried

out a measurement from May to September 2014. The analysis report was received on

September 30, 2014.

Measurement protocol

The measurement report requires per cylinder at least three independent measurements, obtained

under repeatability conditions (at least) with three independent calibration, e.g. calibration (A)

measurement (B) calibration (A) measurement (B) calibration (A) measurement (B)

calibration (A) (etc.).This is a strict requirement to come to proper statistical analysis of the

reported data.

One single measurement result is usually obtained from multiple readings (sub measurements)

without recalibration. Its standard deviation provides information about the performance of the

measurement system.

Measurement methods

Table 1 shows the calibration method, traceability of calibration standards, and the measurement

method at each laboratory.

Table 1: Summary of the measurement methods of the participants

Laboratory Calibration Traceability Matrix of

standards

Measurement

technique

KRISS ISO 6143 [2] Own Nitrogen GC/TCD

6

standards

NMC/A*STAR ISO 6143 Own

standards Nitrogen

ABB paramagnetic

oxygen analyzer

Degrees of equivalence

A unilateral degree of equivalence, Di, is adopted in this comparison.

∆𝑥𝑖 = 𝐷𝑖 = (𝑥𝑙𝑎𝑏,𝑖 − 𝑥𝑟𝑒𝑓,𝑖)

The uncertainty of the difference, Di, corresponds to 95% level of confidence. Here, xlab,i is a

reported value of the APMP.QM-S2.1 sample i from the participating laboratory and xref,i is the

reference value of the APMP.QM-S2.1 sample i and based on the gravimetric concentration

determined by KRISS.

The standard uncertainty of Di can be expressed as;

𝑢2(𝐷𝑖) = 𝑢𝑙𝑎𝑏,𝑖2 + 𝑢𝑟𝑒𝑓,𝑖

2

where ulab,i and uref,i are the uncertainties of xlab,i and xref,i, respectively. The reference value, xref,i

can be expressed as;

𝑥𝑟𝑒𝑓,𝑖 = 𝑥𝑝𝑟𝑒𝑝,𝑖 + ∆𝑥𝑣𝑒𝑟,𝑖 + ∆𝑥𝑙𝑡𝑠,𝑖

where xprep,i is the amount of substance of a target component in APMP.QM-S2.1 sample i and

obtained from gravimetric preparation. The Δxver,i is the difference between the gravimetric value

and measured one during verification analysis. The Δxlts,i is the difference between the

gravimetric value and measured one during long-term stability study which was performed

before and after the sample cylinder for NMC/A*STAR returned to KRISS. Results showed that

Δxver,i and Δxlts,i were smaller than the expanded analytical uncertainty, and thereby both Δxver,i

and Δxlts,i were set to zero.

Assuming independence between errors, the uncertainty of xref,i, uref,i can be expressed as;

𝑢𝑟𝑒𝑓,𝑖2 = 𝑢𝑝𝑟𝑒𝑝,𝑖

2 + 𝑢𝑣𝑒𝑟,𝑖2 + 𝑢𝑙𝑡𝑠,𝑖

2

where uprep,i, uver,i, and, ults,i are the uncertainties of xprep,i , xver,i, and xlts,i, respectively.

In the gravimetric preparation, the amount of a target component is determined by the following

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equation.

𝑥𝑝𝑟𝑒,𝑖 = 𝑥𝑤𝑒𝑖𝑔ℎ𝑖𝑛𝑔,𝑖 + ∆𝑥𝑝𝑢𝑟𝑖𝑡𝑦,𝑖

where xprep,i is the fractional amount of substance of a target component in APMP.QM-S2.1

sample (i), xweighing,i is the fractional amount of substance of a target component in APMP.QM-

S2.1 sample (i) gravimetrically prepared and Δxpurity,i is the correction based on purity analysis.

The uncertainty of the fractional amount is estimated as

𝑢𝑝𝑟𝑒𝑝,𝑖2 = 𝑢𝑤𝑒𝑖𝑔ℎ𝑖𝑛𝑔,𝑖

2 + 𝑢𝑝𝑢𝑟𝑖𝑡𝑦,𝑖2

where uprep,i is the uncertainty from gravimetric preparation, uweighing,i is the uncertainty from

gravimetric weighing process, upurity,i is the uncertainty from purity analysis.

Results

A complete set of results reported from each participant is described in Appendix B of this report.

The results are summarized in Table 1.

Table 1. Summary of measurement results for the comparison. The unit of each parameter is

cmol/mol. The coverage factors, klab, for both laboratories are 2.

Laboratory Cylinder xprep uprep uver ults uref xlab Ulab

cmol/mol

KRISS D081136 20.01823 0.00021 0.005 0.005 0.0071 20.0137 0.0038

NMC

/A*STAR

TAR

D081192 20.04387 0.00021 0.005 0.005 0.0071 20.024 0.015

The parameters in Table 1 are defined as,

xprep amount of substance of target component in APMP.QM-S2.1 sample, from preparation

(cmol/mol)

uprep uncertainty of xprep (cmol/mol)

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uver uncertainty associated with verification (cmol/mol)

ults uncertainty associated with long-term stability test (cmol/mol)

uref uncertainty of reference value (cmol/mol)

xlab reported result from each laboratory (cmol/mol)

Ulab stated uncertainty of each laboratory, at 95% level of confidence (cmol/mol)

klab stated coverage factor

∆x difference between laboratory result and reference value (cmol/mol)

U(∆x) ∆x , at 95% level of confidence (cmol/mol)

Degree of equivalence, Δx, and its expanded uncertainty, U(Δx), of APMP.QM-S2.1 are

summarized in Table 2 and plotted in Fig. 1. The results from the participants are consistent with

the reference values as the deviations from the reference values are within the associated

uncertainties.

Table 2. Summary of Degree of Equivalence for the APMP.QM-S2.1 (k = 2).

Laboratory Cylinder Δx

(cmol/mol)

U(Δx)

(cmol/mol)

Δx/x

(%)

U(Δx)/x

(%)

KRISS D081136 -0.004503 0.014671 -0.0225 0.07329

NMC/A*STAR D081192 -0.01987 0.020641 -0.0991 0.10297

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Figure 1. Degrees of equivalence (k = 2)

Conclusion

This bilateral comparison compares the measurement capability of oxygen in nitrogen matrix at

0.2 mol/mol. The results of both NMC/A*STAR and KRISS agree within 0.1 % with the KCRV.

Reference

[1] International Organization for Standardization, ISO 6142:2001 Gas analysis - Preparation of

calibration gas mixtures - Gravimetric methods, 2nd edition.

[2] 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)

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Appendix A. Verification of mixtures with GC-TCD

Four reference gas mixtures were prepared gravimetrically by KRISS according to ISO 6142.

Table 1 shows a data set of gravimetric concentrations of each cylinder and their relative peak

area of a GC-TCD (HP-7890) compared to a working reference mixture (~20% oxygen in

nitrogen).

Table 1. Analyzed results of four reference gas mixtures of oxygen in nitrogen prepared by

KRISS using a GC-TCD analyzer.

Mixture No.

R

xprep,r

(µmol/mol)

uprep,r

(µmol/mol) yr u(yr)

D325959 204629.0 1.9 1.0230 0.0002

D325944 195244.0 1.9 0.9759 0.00019

D081136(KRISS) 200182.3 2.1 1.0003 0.0002

D081192(A*STAR) 200438.7 2.1 1.0020 0.0002

xprep : gravimetric concentration of reference gas mixtures,

uprep : standard uncertainty of xprep ,

yr : corrected response relative to a QC cylinder (D155880, ~20% oxygen in nitrogen) of GC-

TCD,

u(yr) : standard uncertainty of yr

Linear regression result of xprep,r versus yr in Table 1 is shown in Table 2. The uncertainty of the

linear regression fit is also shown in Table 2.

Table 2. Parameters of a linear regression fit, y = a0 + a1 · x

Parameter Value

a0 -0.00525

u(a0) 0.00742

a1 5.02467×10-6

u(a1) 3.70584×10-8

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Adj. R-Square 0.99984

After the regression analysis of table 2, the values of xver,i in the following table 3 were

calculated using the parameters and the equation in table 2 and the values of yr in table 1.

Table 3. Comparison with gravimetric concentration and the result of analytical concentration.

Mixture No.

r

xprep,r uprep,r xver,r uver,r ∆xver,r U(∆xver,r)

µmol/mol

D325959 204629.0 1.9 204644 51.2 15.3 102.4

D325944 195244.0 1.9 195259 48.8 15.3 97.7

D081136(KRISS) 200182.3 2.1 200123 50.0 -59.2 100.2

D081192(A*STAR) 200438.7 2.1 200467 50.1 28.9 100.3

xver,r : analytical concentration of reference gas mixture, (yr = a0 + a1·xver,r)

uver,r : standard uncertainty of xver,r ,

∆xver,r = xver,r – xprep,r : deviation of verification for mixture r.

Uver,r : expanded uncertainty of yr (coverage factor, k=2).

The corrected responses of GC-TCD, yr were obtained as follows. The responses of the analyzer

were corrected with a quality control (QC) cylinder. The QC cylinder gas and other cylinder

gases were injected sequentially into the analyzer using a multi-positioning valve.

Cylinder gases were measured in the following order.

“QC(i =1) − calibration standard 1 − QC(i =2) − calibration standard 2 − QC(i =3) − calibration

standard 3 − QC(i =4) − calibration standard 4 − QC(i =5)”

In each step of the cycle, measurement of the gas analyzer was repeated 5 times for each cylinder.

The last 4 measured results were used for the calculation. This process (“QC(i=1) − ··· − QC(i

=5)”) were repeated j times (j = 3).

The following calibration data set can be obtained at jth

round (j = 1, 2, 3);

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- Average values of responses to the QC cylinder, Yqc,i=1,j , …. , Yqc,i=4, j ,

- Average values of responses for calibration standards, Y1, j , Y2, j , Y 3, j , Y 4, j.

The corrected response for calibration standard r at jth

round, yr, j , was calculated as follows;

yr, j = Yr, j / [(Yqc,i=r, j + Yqc,i=r+1, j )/2] (r = 1, 2, 3, 4) (1)

The value of yr was calculated from the following equation;

𝑦𝑟 = ∑ 𝑦𝑟,𝑗/𝐽𝑗=3𝑗=1 (2)

These standard uncertainties are [Ref. 1];

𝑢2(𝑦𝑟) = ∑(𝑦𝑟,𝑗−𝑦𝑟)

2

𝐽(𝐽−1)

𝑗=3𝑗=1 (3)

The gravimetrically prepared mixtures have been verified by comparing the gravimetric

composition value with its analytical measurement value (i.e., verification value) as shown in the

following condition.

|𝑥𝑝𝑟𝑒𝑝,𝑟 − 𝑥𝑣𝑒𝑟,𝑟| ≤ 2√𝑢𝑝𝑟𝑒𝑝,𝑟2 + 𝑢𝑣𝑒𝑟,𝑟2 (4)

where xver,r and uver,r is the measurement result from verification and its the standard uncertainty,

respectively. The uncertainty associated with the verification relies on the measurement

capability and experiment design. In the comparison with gravimetric concentration and

analytical concentration for each mixture, all values of ∆xver,r were smaller than those of

U(∆xver,r).

Reference

[1] International Organization for Standardization, ISO 6142:2001 Gas analysis - Preparation of

calibration gas mixtures - Gravimetric methods, 2nd edition.

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Appendix B. Report from each laboratory

Laboratory: KRISS (Korea Research Institute of Standards and Science), Korea

Cylinder number: D081136

Measurement 1#

Component Date

(dd/mm/yy)

Result

(cmol/mol)

Standard

deviation

(% relative)

Number of

replicates

O2 27/03/15 20.0120 0.0074 3

Measurement 2#

Component Date

(dd/mm/yy)

Result

(cmol/mol)

Standard

deviation

(% relative)

Number of

replicates

O2 28/03/15 20.0158 0.018 3

Measurement 3#

Component Date

(dd/mm/yy)

Result

(cmol/mol)

Standard

deviation

(% relative)

Number of

replicates

O2 29/03/15 20.0134 0.0081 3

Results

Component Result

(cmol/mol)

Expanded uncertainty

(cmol/mol) Coverage factor*

O2 20.0137 0.0038 (0.0192 %) 2

*The coverage factor shall be based on approximately 95% confidence.

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Calibration Standards

Four reference gas mixtures were prepared by gravimetric method according to ISO 6142.

Cylinder Number Assigned value

(cmol/mol)

Standard uncertainty

(cmol/mol)

D325944 19.5244 0.00019

D081136 20.01823 0.00021

D081192 20.04387 0.00021

D325959 20.4629 0.00019

-Gravimetric preparation data

Primary standard gas mixtures were prepared gravimetrically according to ISO6142.

Specification of a balance

Model No.: Mettler-Toledo

Resolution: 1 mg, Capacity: 10 kg

Uncertainty (k = 2): 3.2 mg

Weighing method (A-B-A, substitution method)

Substitution method, tare cylinder (A-B-A)

-Purity Analysis

Nitrogen source gas: 99.99932%mol/mol

Component Amount fraction

(10-6

mol/mol)


(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

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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

Oxygen source gas: 99.99978%mol/mol

Component Amount fraction

(10-6

mol/mol)


(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

Sample handling

The sample cylinder was stored at a room temperature for 3 days before an analysis. The

reference cylinder was also stored at the same condition. The room temperature of our laboratory

was maintained at ~22 ± 2 °C for all the period.

A SS regulator was connected to the reference and sample cylinders. The reference and sample

gases were directly introduced to the GC through a multi-positioning valve and a mass flow

controller.

The injection of gases was switched automatically using a multi-positioning valve.

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Instrumentation

-Analytical Instrument: HP7890A GC analyzer equipped with a TCD detector and sampling

valve line without an injection port

-Analytical Condition

Condition

Detector Thermal Conductivity Detector (TCD)

Detector Temperature 250°C

Carrier Flow rate 80 psi

Reference Flow rate 45 mL/min

Column Resteck Molesieve 5A, 4m, 1/8”, SS

Oven Temperature 60°C for 12min

Valve Box Temperature 60°C

Sample Flow rate 75 mL/min

Sample Loop Volume 100 µL

Instrument Calibration

The corrected responses of GC-TCD, yr were obtained as follows. The responses of the analyzer

were corrected with a quality control (QC) cylinder. The QC cylinder gas and other cylinder

gases were injected sequentially into the analyzer using a multi-positioning valve.

Cylinders were measured in the following order.

“QC(i =1) − calibration standard 1 − QC(i =2) − calibration standard 2 − QC(i =3) − calibration

standard 3 − QC(i =4) − sample gas − QC(i =5) − sample gas − QC(i =6) − sample gas − QC(i

=7)”

In each step of the cycle, measurement of the gas analyzer was repeated 5 times for each cylinder.

The last 4 data were used for the calculation. This process was repeated 3 times during three

different days.

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During each measurement period (j =1, 2, 3), following calibration data set can be obtained.

- Average values of responses to the QC cylinder, Yqc,i=1,j , …. , Yqc,i=5, j,

- Average values of responses for calibration standards and sample gas, Y1,j , Y2, j , Y3, j , Ys, j, Ys, j,

Ys, j.

The corrected response for calibration standard r at jth

period, Yr, j, was calculated as follows.

yr, j = Yr, j / [(Yqc, i=r, j + Yqc, i=r+1, j )/2] ( r = 1, 2, 3 ) (1)

ys, j = Ys, j / [(Yqc, i=r, j + Yqc, i=r+1, j )/2] ( r = 4, 5, 6 ) (2)

From the data set of Xr=1 (reference value of calibration standard 1), Xr=2, Xr=3, yr=1, j, yr=2, j and

yr=3, j, the linear regression parameters were obtained from a linear fit of yr, j = b0 + b1·Xr. From

the regression parameters, mixing ratios of sample cylinder, Xs were calculated from ys, j.

Uncertainty evaluation

Typical evaluation of the measurement uncertainty of O2:

Uncertainty [cmol/mol] Uncertainty [%]

Gravimetric uncertainty

-Purity analysis

-Gravimetric method

-Molar mass

0.00021 0.001

Analytical uncertainty

-Repeatability

-Reproducibility

0.0019 0.0096

Combined uncertainty 0.0019 0.0096

Expanded uncertainty (k=2) 0.0038 0.0192

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Report Form oxygen in nitrogen

Laboratory name: Gas Metrology Laboratory, National Metrology Centre,

Singapore

Cylinder number: KRISS Cylinder (D081192, 00T-3AL2610 0081192 M-9905)

Measurement 1#

Component Date

(dd/mm/yy)

Result

(mol/mol)

Standard

deviation

(% relative)

Number of

replicates

O2 29/07/2014 0.200234 0.061961 3

O2 29/07/2014 0.200257 0.063038 3

O2 29/07/2014 0.200283 0.064391 3

Measurement 2#

Component Date

(dd/mm/yy)

Result

(mol/mol)

Standard

deviation

(% relative)

Number of

replicates

O2 30/07/2014 0.200214 0.061121 3

O2 30/07/2014 0.200205 0.060757 3

O2 30/07/2014 0.200271 0.063762 3

Measurement 3#

Component Date

(dd/mm/yy)

Result

(mol/mol)

Standard

deviation

(% relative)

Number of

replicates

O2 31/07/2014 0.200218 0.061247 3

19

O2 31/07/2014 0.200261 0.063291 3

O2 31/07/2014 0.200195 0.060329 3

Results

Component Result

(mol/mol)

Expanded uncertainty

(mol/mol)

Coverage factor*)

O2 0.20024 0.00015 k=2

*) The coverage factor shall be based on approximately 95% confidence.

Method description forms

Please complete the following data regarding the description of methods and the uncertainty

evaluation.

Reference Method:

The analysis was performed on three different days with ABB paramagnetic oxygen analyzer

with the sampling box. The gas flow rate was set at 350ml/min. The mole fraction of the

compared cylinder was calculated by interpolation of a calibration curve using CurveFit software.

Calibration standard:

The below standards were prepared by gravimetric method according to ISO6142. The purity of

gases was analysed with GC PDHID. The cylinders used were 5L aluminum with Aculife 3

treatment from Scott Specialty Gases. The regulator used was SS verifo single stage without

gauges purged 5 times according to operational procedure.

PSM Number Mol fraction Standard uncertainty (relative)

PSM118652 0.19005899 4.46703E-05

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PSM118645 0.19949439 4.32092E-05

PSM118641 0.20010219 4.32779E-05

PSM118643 0.20058766 4.30734E-05

PSM118651 0.20977828 4.18060E-05

Instrument calibration:

The analyzer was adjusted in zero and span before every analysis. The above PSM were used as

the calibration curve.

Sampling handing:

The received cylinders and NMC PSM were maintained inside the laboratory at room

temperature for all the time. Modified Teflon was used for sample lines. The sampling to the

analyzer and measurement were done under ambient pressure, and the pressure correction and

response correction were included in the calculation.

Detailed uncertainty budget:

Please include a list of the uncertainty contributions, the estimate of the standard uncertainty,

probability distribution, sensitivity coefficients, etc.

Typical evaluation of the measurement uncertainty of O2:

Quantity

(Uncertainty

source), Xi

Estimate,

xi

Evaluation

type (A or B) Distribution

Standard

uncertainty,

u(xi)

Sensitivity

coefficient,

ci

Contribution,

u(yi)

Gas standard 0.190060 Type B Normal 4.46703E-05 1 4.46703E-05



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Repeatability 0.200237 Type A Normal 0.00035917 1 0.00035917

Combined

uncertainty

(relative)

0.000372

Expanded

uncertainty

(relative)

0.000744

Expanded

uncertainty

(mol/mol)

0.00015

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