International Supplementary Comparison

COOMET.QM-S3 (COOMET project № 608/RU/13)

COMPARISON OF PRIMARY STANDARD GAS MIXTURES: GRAVIMETRIC PRODUCTION OF CO IN NITROGEN (3 μmol/mol)

Saint - Petersburg 2014

Final report

L.A. Konopelko1, Y.A. Kustikov1, A.V. Kolobova1, V.V. Pankratov1, A.A. Pankov1,

O.V. Efremova1, Cristiane R. Augusto2, Andreia L. Fioravante2, Claudia C. Ribeiro2, Denise

C.G.S. Teixeira2, Elizandra C.S. Elias2, Rutger J. Oudwater2, Fátima A. Fagundes2, Marceli

C.Silva2

1 D.I. Mendeleyev Institute for Metrology (VNIIM), 19 Moskovsky Prospekt, 190005, St-

Petersburg, Russia;

2 Instituto Nacional de Metrologia (Inmetro), Qualidade e Tecnologia Av. Nossa Senhora

das Graças, 50 - Xerém - cep: 25.250-020, Prédio 4 - Duque de Caxias - RJ - Brasil

Field

Amount of substance: Gas analysis

Subject

Supplementary comparison of primary standard gas mixtures – Carbon monoxide in

Nitrogen (3 μmol/mol)

Participants

VNIIM (Russia), Inmetro (Brazil)

Organizing body

TC 1.8 «Physical Chemistry» COOMET

3

1. Background

Carbon monoxide (CO) is present in the atmosphere due to different natural and

antropogenic sources. Ambient CO ranges from 50 to 300 nmol/mol at marine boundary

and from 100 to 500 nmol/mol at city area. Carbon monoxide is a toxic gas and in

concentrations higher than 3-5 mol/mol it is hazardous to human health.

The Consultative Committee for Amount of Substance (CCQM) has carried out 2

comparisons involving CO. The first at 5 µmol/mol in nitrogen (CCQM-K51) and the

second at 350 nmol/mol in air and (CCQM-K84).

This bilateral comparison was proposed within the cooperation program in the field of

metrology between VNIIM and INMETRO. In 2013 it was registered as COOMET

supplementary comparison.

2 Conduct of the Comparison The participants prepared gas mixtures for the comparison gravimetrically in accordance

with requirements of ISO 6142 [1] and studied regarding their composition and stability in

accordance with requirements of ISO 6143 [2].

All the primary standard gas mixtures (PSGMs) were prepared in cylinders of 5 dm3

nominal and with pressure approximately 10,0 MPa.

Inmetro prepared 3 PSGMs of carbon monoxide in nitrogen on the level of 3 mol/mol and

carried out verification measurements by checking consistency between three nominally

similar prepared mixtures and also by comparison with older VSL’s PRM. After verification

and stability testing, one of the prepared PSGMs was sent to VNIIM for measurements.

VNIIM prepared 1 PSGM of carbon monoxide in nitrogen on the level of 3 mol/mol,

carried out verification measurements by comparison with 3 earlier prepared PSGMs of

CO in nitrogen. Then the Inmetro PSGM was measured with reference to 4 VNIIM

PSGMs.

3 Measurement protocol The measurement protocol requested each laboratory to perform at least 3 measurements

obtained under repeatability conditions including at least three separate calibrations. The

protocol informed the participants about the nominal concentration of carbon monoxide in

the gas mixture. The laboratories were also requested to submit a summary of uncertainty

evaluation for the presented results.

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4 Measurement methods, calibration and verification procedures Summary of measurement and calibration (verification) methods is shown in table 1. Table 1 Measurement and calibration methods

Laboratory Measurement method

Calibration and verification method

Total number of measurements

Inmetro GC-PDHID One point calibration 3 own standards

3 measurements 10 sub-measurements

VNIIM NDIR Calibration curve 4 own standards

4 measurements 4 sub-measurements

Description of measurement procedure of Inmetro PSGM in VNIIM is shown in the

Appendix A.

5 Results The results of measurement of carbon monoxide mole fraction in the Inmetro PSGM

(cylinder N D247521) are shown in table 2

Table 2 Measurement results Inmetro VNIIM

x1grav

mol/mol

ux1, = 0,0167

mol/mol

x1pred

mol/mol

u x1,pred = 0,0028

mol/mol

ux1,grav ux1,ver ux2,grav umeas.

3.1401 0.0035 0.0163 3.1644 0.0013 0.0025

where

x1,grav – amount of substance fraction of CO in PSGM, assigned from gravimetry in Inmetro;

ux1,grav – standard uncertainty of gravimetrical preparation and purity for Inmetro PSGM;

ux1,ver - standard uncertainty from verification for Inmetro PSGM;

ux1, – combined standard uncertainty for Inmetro PSGM;

x1,pred - amount of substance fraction of CO in Inmetro PSGM predicted from VNIIM

measurements;

ux2,grav - standard uncertainty of gravimetrical preparation and purity for VNIIM PSGM;

umeas. - standard uncertainty of measurements in VNIIM (standard deviation of the

measurement result);

ux1,pred - combined standard uncertainty of predicted amount of substance fraction from

VNIIM measurements of Inmetro PSGM, 22

2 measgrav,xpredx1, uuu ;

5

6 Degree of equivalence

The pair-wise degree of equivalence D in this comparison is defined in accordance with the

equation:

gravpred xx1 D 1 (1) ;

D 0.0243 mol/mol

The standard uncertainty of the pair-wise degree of equivalence can be expressed as:

2

gravx1,

2

predx1, uu)D(u (2);

Du =0.0045 mol/mol

The expanded uncertainty )D(U at a 95 % confidence level will be:

2

gravx1,

2

predx1, uuk)D(U (3);

DU =0.0090 mol/mol

where k is a coverage factor, k=2

7 Final results

Table 3 final comparison results

Laboratory Cylinder № xi,grav

mol/mol

uxi,grav

mol/mol

umeas

mol/mol

xi,pred

mol/mol

uxi,pred

mol/mol

D mol/mol (% rel.)

k U(D) mol/mol (% rel.)

Inmetro D247521 3.1401 0.0035 - 3.1644 0.0028 0.0243 (0.77)

2 0.0090 (0.29) VNIIM D158042 3.0065 0.0013 0.0025 - -

Figure 1 illustrates graphically the difference between the INMETRO value (gravimetric) and VNIIM measured value (predicted). Uncertainty bars are shown at k=2. Figure 1

6

8 How Far Does the Light Shine This supplementary comparison aims to support CMC claims for carbon monoxide from 1

μmol/mol and higher in a nitrogen matrix. This key comparison can also be used to support

CMC claims for carbon monoxide in an air matrix with special consideration for cross

interference from the high concentration of oxygen on the CO concentrations especially with

measurement techniques, such as NDIR.

9 Conclusions The present comparison has shown that primary standard gas mixtures of carbon monoxide

in nitrogen on the level of 3 mol/mol, prepared in VNIIM and Inmetro, do not agree – the

pair-wise degree of equivalence D (0.77 %) is higher than the appropriate expanded

uncertainty U(D) (0.29 %).

After the analysis of the possible reasons of discrepancy in the results of VNIIM and Inmetro,

participants agreed that the assigned value of CO mole fraction in Inmetro gas mixture is

possibly understated (compared with the VNIIM measured value) due to underestimation of

CO mole fraction in the pure matrix gas nitrogen while measuring by GC-PDHID, carried out

by Inmetro. It is also possible that uncertainty of CO mole fraction in Inmetro gas mixture

was underestimated, as the purity assessment of parent gases in Inmetro was carried out

mainly in accordance with manufacturer specification.

References [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 6143:2001 Gas analysis –

Comparison methods for determining and checking the composition of calibration gas

mixtures.

Coordinator

Leonid Konopelko

VNIIM, Research Department for the State Standard in the Field of Physical-Chemical

Measurements (PCD),

19, Moskovsky pr., St.-Petersburg, 198005, Russia

Phone: +7 812 3151145

E-mail: lkonop@b10.vniim.ru Completion Date February 2014

ANNEX А

Description of measurement procedure of Inmetro PSGM in VNIIM

Measurement of carbon monoxide mole fraction in the investigated gas mixture (Inmetro

cylinder № D247521) in the pilot laboratory was performed by NDIR on the optoacoustic

gas analyzer AERONICA-СО (optical path 1000 мм, noise 10 ppb)

4 primary standard gas mixtures (prepared at different times and from different parent

gases) were used for calibration:

PSGM with СО mole fraction 0,500 0,007 млн−1 (k=2), cylinder № 0773 (С1),

PSGM with СО mole fraction 1,004 0,007 млн−1 ( k=2), cylinder № 3934 (С2),

PSGM with СО mole fraction 3,013 0,007 млн−1 ( k=2), cylinder № 1276 (CCONTROL),

PSGM with СО mole fraction 3,0065 0,0026 млн−1 ( k=2), cylinder № D158042 (СVNIIM),

And also primary standard pure gas PSPG N2 with СО mole fraction 1.0 1,2 ppb ( k=2),

cylinder № D910253 (СZERO), which was used as zero gas mixture in order to obtain

analytical signal in the absence of СО in a cuvette with gas mixture, as well as for

compensation of drift of zero.

The sequence of gas mixtures injection during measurements of СО mole fraction in

Inmetro cylinder (СINMETRO) was as follows:

СZERO CCONTROL С1 С2 CCONTROL СZERO CCONTROL СINMETRO. СVNIIM

CCONTROL СZERO

All in all 4 measurement series were carried out (in different days) with 4 identic cycles

(sub-measurements).

Analytical signals excluding zero signal (taking into consideration its drift) were calculated

for CCONTROL, С1С,СINMETRO,СVNIIM. The values were divided by analytical signal of

CCONTROL (taking into consideration its drift) to obtain the ratios. 4 ratios were collected for

each PSGS within 1 series, which were averaged. The ratios and gravimetric

concentrations were then plotted (with GLS programme) to obtain graph Y=b0+b1*X,

where Y - amount of substance fraction of CO in PSGM assigned from gravimetry,

mol/mol; X – ratio of analytical signal in investigated mixture to signal in the control

mixture.

The results of the regression are shown in the table A1.

Table A1 Results of measurements

Instrument Aeronica СО, cuvette 1000 mm

Gas mixture flow 1 l/min

N2 flow 1 l/min

Dates of measurements 25-28.11.2013

Cylinder (N)

СО mole fraction,

mol/mol by

gravimetry

u (k=1),

mol/mol

Pressure in the

cylinder, MPa

Cylinder

Ratios of signals (R) Cx/Ccontrol

1 meas. 2 meas. 3 meas. 4 meas. Average (Rav)

St.dev St.dev. %

СZERO (D910253) 0,001 0,0006 3,5 CCONTROL 1,000000 1,000000 1,000000 1,000000 1,000000

CCONTROL (1276) 3,013 0,0035 8 C1 0,165531 0,163590 0,164320 0,165910 0,164838 0,001073 0,651063

C1(0773) 0,5 0,0035 9 C2 0,331450 0,332150 0,332432 0,331210 0,331811 0,000575 0,173310

C2(3934) 1,004 0,0035 7,5 CCONTROL 1,000000 1,000000 1,000000 1,000000 1,000000

CCONTROL (1276) 3,013 0,0035 8 CINMETRO 1,047150 1,049195 1,048214 1,048442 1,048250 0,000845 0,080593

СZERO (D910253) 0,001 0,0006 3,5 CVNIIM 0,995190 0,995775 0,994478 0,994328 0,994943 0,000670 0,067365

CCONTROL (1276) 3,013 0,0035 8 CCONTROL 1,000000 1,000000 1,000000 1,000000 1,000000

CINMETRO(D247521) 3,14010 0,0035 5,0

CVNIIM(D158042) 3,0065 0,0013 9,5

CCONTROL (1276) 3,013 0,0035 8,0 Cylinder

Ci grav

mol/mol Rav

xi pred

mol/mol St.dev,

% Ci pred-

Cigrav, %

СZERO (D910253) 0,001 0,0006 3,5

CCONTROL 3,013 1,000000 3,0188 0,1924992

C1 0,5 0,164838 0,499115 0,64872 -0,176902

C2 1,004 0,331811 1,002872 0,173 -0,112323

Y=b0+b1*X CCONTROL 3,013 1,000000 3,0188 0,1924992

CINMETRO 3,14010 1,048250 3,164371 0,08055 0,7729445

b0 0,001788 u(b0)= 0,002468 CVNIIM 3,0065 0,994943 3,003542 0,06732 -0,098378

b1 3,017028 u(b1)= 0,003281 CCONTROL 3,013 1,000000 3,0188 0,1924992

S 4,816529237 u(b0,b1)= -6,572E-06

Annex B

Reports submitted by participating laboratories

INMETRO REPORT

COOMET.QM-S3 (COOMET project № 608/RU/13)

COMPARISON OF PRIMARY STANDARD GAS MIXTURES:

CARBON MONOXIDE IN NITROGEN (3μmol/mol)

1 INFORMATION ABOUT PARTICIPATING INSTITUTE:

Institute Inmetro – Instituto Nacional de Metrologia, Qualidade e Tecnologia

Address Av. Nossa Senhora das Graças, 50 - Xerém - cep: 25.250-020 Prédio 4 - Duque de Caxias - RJ - Brasil

Contact Person Cristiane Rodrigues Augusto, Andreia de Lima Fioravante

NMI Participants Cristiane R. Augusto, Andreia L. Fioravante, Claudia C. Ribeiro, Denise C.G.S. Teixeira, Elizandra C.S. Elias, Rutger J. Oudwater, Fátima A. Fagundes, Marceli C.Silva

Telephone (++55) (21) 2679-9243

Fax (++55) (21) 2679-9069

email craugusto@inmetro.gov.br, aalima@inmetro.gov.br

2CYLINDER DETAILS

Date of mixture preparation 12/03/2013

Volume (L) 5

Total Pressure (bar) 100

3.1 PURITY TABLE FOR NOMINALLY PURE CO (OR CO PARENT MIXTURE)

CYLINDER N WM2472 (SUPPLIER: WHITE MARTINS)

Component Method* Mole Fraction

(mol/mol)

Standard uncertainty

(mol/mol)

CH4 specification 1,00 0,58

N2 specification 2,50 1,44

CO2 specification 1,00 0,58

H20 specification 1,00 0,58

O2 specification 1,00 0,58

CO 999993,50 1,85

* this may refer to an analytical method (e.g. GC-FID) if you analysed for this impurity. If you are relying on suppliers specifications for this impurity estimate, enter “specification”.

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3.2 PURITY TABLE FOR NOMINALLY PURE N2

CYLINDER N401153 (SUPPLIER: WHITE MARTINS)

Component Method* Mole Fraction

(mol/mol)

Standard uncertainty

(mol/mol)

Ar GC-PDHID 335,58 0,11

CO GC-PDHID 0,1860 0,0035

O2 specification 0,25 0,14

H20 specification 0,25 0,14

THC specification 0,05 0,03

N2 999663,69 0,23

* this may refer to an analytical method (e.g. GC-FID) if you analysed for this impurity. If you are relying on suppliers specifications for this impurity estimate, enter “specification”.

4. PURITY TABLE FOR FINAL CO/N2MIXTURE

CYLINDER N:D247521

Component Mole Fraction

(mol/mol)

Standard uncertainty*

(mol/mol)

Ar 335,58 0,11

CO 3,1401 0,0035

CO2 0,0000029 0,0000017

O2 0,25 0,14

H20 0,25 0,14

THC 0,05 0,05

N2 999660,73 0,22

* Please place here only gravimetric (including purity assessment) standard uncertainty

Notes:

1 There were prepared 3 similar PSMs with slightly different CO concentrations – 3,00; 3,14 and

2,97mol/mol by 3 step dilution (4,0 %, 0,16 %, 60 mol/mol) from the same pure gases.

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5. VERIFICATION

Verification was carried out by checking consistency between three nominally similar prepared mixtures and also by comparison with older VSL’s PRM. Analytical method –GC-PHDID The reference values for the amount-of-substance fractions are obtained by interpolation using a calibration curve. The following results are presenting the uncertainty as standard deviation of the measurements, with 10 (ten) repetitions in 03 (three) different days. The results have been fitted using a linear function, in accordance with ISO 6143, using the software b-least.

What CO mole fraction was predicted from your verification analysis?

XCO,anal: 3,1275 mol/mol

What is your estimate of the uncertainty (standard) in xCO,anal ?

u(xCO,anal) : 0,0163 mol/mol

6. STABILITY TESTING

Briefly describe any measures undertaken to confirm the stability of the mixtures in the period between their preparation and their shipping to the coordinator

The stability of the PSM is ensured by previous investigations.

If necessary, standard uncertainty due to stability u(xCO,stab) may be included here

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VNIIM REPORT

COOMET.QM-S3 (COOMET project № 608/RU/13)

COMPARISON OF PRIMARY STANDARD GAS MIXTURES:

CARBON MONOXIDE IN NITROGEN (3μmol/mol)

1 INFORMATION ABOUT PARTICIPATING INSTITUTE:

Institute VNIIM

D.I. Mendeleyev Institute for Metrology

Address 19, Moskovsky pr., St. Petersburg, 198005, Russia

Contact Person Leonid Konopelko

Telephone +7 (812) 315-11-45

Fax +7 (812) 327-97-76

email lkonop@b10.vniim.ru

2 CYLINDER DETAILS

Date of mixture preparation 20.11.2013

Volume (L) 5

Total Pressure (bar) 100

3.1 PURITY TABLE FOR NOMINALLY PURE CO (OR CO PARENT MIXTURE)

Complete for all components considered:

Component Method Mole Fraction

(mol/mol)

Standard uncertainty

(mol/mol)

Ar GC-TCD 0.50 0.29

CH4 GC-TCD 0.50 0.29

CO2 GC-TCD 35.6 0.3

H2 GC-TCD 73.7 0.3

He GC-TCD 10.20 0.13

N2 GC-TCD 320 6

O2 GC-TCD 4.85 0.10

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3.2 PURITY TABLE FOR NOMINALLY PURE N2

Complete for all components considered:

Component Method Mole Fraction

(mol/mol)

Standard uncertainty

(mol/mol)

Ar GC-PDHID 0.295 0.004

CH4 GC-FID 0.0025 0.0014

CO GC-FID+methanator 0.0010 0.0006

CO2 GC-FID+methanator 0.0277 0.0010

H2 GC-PDHID 0.0025 0.0014

H2O Hygrometer 0.500 0.017

O2

Coulometric analyzer 0.01410 0.0009

4. PURITY TABLE FOR FINAL CO/N2 MIXTURE

Complete for all components considered:

Component Mole Fraction

(mol/mol)

Standard uncertainty*

(mol/mol)

CO 3.0065 0.00134

N2 balance -

* Please place here only gravimetric (including purity assessment) standard uncertainty

5. VERIFICATION

Briefly describe your verification procedure. For example was it by comparison with other traceable CO/N2 standards; how many such standards; which analytical methods were used?

Verification was carried out by checking consistency between newly prepared CO/N2 gas mixture and three older VNIIM measurement standard mixtures. Analytical method - NDIR

What CO mole fraction was predicted from your verification analysis?

XCO,anal: 3.003 mol/mol

What is your estimate of the uncertainty (standard) in xCO,anal ?

u(xCO,anal) : 0.0025 mol/mol

6. STABILITY TESTING

Briefly describe any measures undertaken to confirm the stability of the mixtures in the period between their preparation and their shipping to the coordinator

The stability of the PSM is ensured by previous investigations.

If necessary, standard uncertainty due to stability u(xCO,stab) may be included here