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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: [email protected] 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 [email protected], [email protected]
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 [email protected]
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