CCQM K101 1 CCQM K101 Final Report International Comparison CCQM-K101: Oxygen in Nitrogen _ a Track B Comparison and That the Matrix Contains Argon Zeyi Zhou 1 ,Qiao Han 1 , Defa Wang 1 , Tatiana Macé 2 ,Heinrich Kipphardt 3 , Michael Maiwald 3 ,Dirk Tuma 3 , Shinj Uehara 4 , Dai Akima 4 , Takuya Shimosaka 5 ,Jinsang Jung 6 , Sang-Hyub Oh 6 , Adriaan van der Veen 7 , Janneke I.T. van Wijk 7 , Paul R. Ziel 7 , Leonid Konopelko 8 , Miroslava Valkova 9 , David M Mogale 10 , Angelique Botha 10 , Paul Brewer 11 , Arul Murugan 11 , Marta Doval Minnaro 11 , Michael Miller 11 , Frank Guenther 12 , Michael E. Kelly 12 1 National Institute of Metrology(NIM),Beijing Beisanhuan East road Nop.18, Beijing 100029, China. 2 Laboratoire National de Metrologie et D'essais (LNE), 1, rue Gaston Boissier, 75 724 Paris Cedex 15, France. 3 BAM Federal Institute for Materials Research and Testing (BAM), Division 1.4, Gas Analysis/Gasanalytik 40/423, Unter den Eichen 87, 12205 Berlin, Germany. 4 Chemicals Evaluation and Research Institute (CERI),1600 Shimotakano, Sugito-machi, Kitakatsushika-gun, Saitama 345-0043, Japan. 5 National Metrology Institute of Japan(NMIJ),1-1-1 Umezono, Tsukuba, Ibaraki, 305-8563, Japan. 6 Korea Research Institute of Standards and Science (KRISS ),267 Gajeong-ro Yuseong-gu Daejeon, 305-340, the Republic of Korea. 7 Netherlands Meetinstituut Van Swinden Laboratory (VSL), Thijsseweg 11, 2629 JA Delft, The Netherlands. 8 D.I. Mendeleyev Institute for Metrology (VNIIM) , 19 Moskovsky pr., St. Petersburg, 190005, Russia. 9 Slovak Institute of Metrology(SMU), Karloveska 63, SK-842 55 Bratislava, Slovakia. 10 National Metrology Institute of South Africa(NMISA), CSIR Campus, Meiring Naudé Road, Brummeria, Pretoria, South Africa . 11 National Physical Laboratory(NPL), Hampton Road, Teddington, Middlesex, TW11 0LW. 12 National Institute of Standards and Technology (NIST ), 100 Bureau Drive, Gaithersburg, MD 20899-8393.
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International Comparison CCQM-K101:Oxygen in Nitrogen10National Metrology Institute of South Africa(NMISA), CSIR Campus, Meiring Naudé Road, Brummeria, Pretoria, South Africa
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CCQM K101
1
CCQM K101 Final Report
International Comparison CCQM-K101:Oxygen in Nitrogen _ a
Track B Comparison and That the Matrix Contains Argon
Zeyi Zhou1,Qiao Han
1, Defa Wang
1, Tatiana Macé
2,Heinrich Kipphardt3, Michael
Maiwald3,Dirk Tuma
3, Shinj Uehara 4
, Dai Akima4, Takuya Shimosaka
5,Jinsang
Jung6,Sang-Hyub Oh
6, Adriaan van der Veen
7,Janneke I.T. van Wijk7,Paul R. Ziel
7,Leonid Konopelko
8,Miroslava Valkova9,David M Mogale
10, Angelique Botha
10,Paul
Brewer11
, Arul Murugan11
, Marta Doval Minnaro11
, Michael Miller11 , Frank
Guenther12
, Michael E. Kelly12
1National Institute of Metrology(NIM),Beijing Beisanhuan East road Nop.18,
Beijing 100029, China. 2Laboratoire National de Metrologie et D'essais(LNE),1, rue Gaston Boissier, 75 724
Paris Cedex 15, France. 3BAM Federal Institute for Materials Research and Testing(BAM),Division 1.4, Gas
Analysis/Gasanalytik 40/423, Unter den Eichen 87, 12205 Berlin, Germany. 4Chemicals Evaluation and Research Institute (CERI),1600 Shimotakano,
Sugito-machi, Kitakatsushika-gun, Saitama 345-0043, Japan. 5National Metrology Institute of Japan(NMIJ),1-1-1 Umezono, Tsukuba, Ibaraki,
305-8563, Japan. 6Korea Research Institute of Standards and Science(KRISS),267 Gajeong-ro
Yuseong-gu Daejeon, 305-340, the Republic of Korea. 7 Netherlands Meetinstituut Van Swinden Laboratory(VSL),Thijsseweg 11, 2629 JA
Delft, The Netherlands. 8D.I. Mendeleyev Institute for Metrology(VNIIM), 19 Moskovsky pr., St. Petersburg,
190005, Russia. 9Slovak Institute of Metrology(SMU), Karloveska 63, SK-842 55 Bratislava,
Slovakia. 10
National Metrology Institute of South Africa(NMISA), CSIR Campus, Meiring
Naudé Road, Brummeria, Pretoria, South Africa
.11
National Physical Laboratory(NPL), Hampton Road, Teddington, Middlesex,
TW11 0LW. 12
National Institute of Standards and Technology(NIST) , 100 Bureau Drive,
Gaithersburg, MD 20899-8393.
CCQM K101
2
Coordinating Laboratory: National Institute of Metrology (NIM)
Study Coordinator: Zeyi Zhou
Field: Amount of substance
Subject: Oxygen in Nitrogen at 10 mol/mol
Organizing Body: CCQM
Schedule of comparison:
Protocol issued April 2012, Paris
June 2012 Preparation cylinder and verification
Oct.2012 ~Feb. 2013 Cylinders shipped to participating labs
Sept. ~ Nov. 2013 Reports and Cylinders back to NIM for verification
Nov. 2013~April 2014 Prepare report of K101
April 2014 Draft A report issued
Sept. 2014 Draft B report issued
1. Introduction
This key comparison aims to assess the capabilities of the participants to determine
the amount-of-substance fraction oxygen in nitrogen. The GAWG has classified this
as a Track B comparison, due to the unexpected 50 mol/mol Argon mole fraction
content of the transfer standards, which effects the achievable performance of some
measurement techniques such a GC-TCD. The separation of oxygen and argon is a
challenging, and not all systems in use are equally well designed for it. As this
analytical challenge due to a substantial fraction of Argon in the transfer standards
became a reality, the Gas Analysis Working Group (GAWG) decided to qualify this
key comparison as a regular key comparison and not as a core comparison, which
may be used to support calibration and measurement capabilities (CMCs) for oxygen
in nitrogen, or for oxygen in nitrogen mixtures containing argon only (see also the
section on support to CMCs).
Support to CMCs
This key comparison provides evidence in support of CMCs for oxygen in the
amount-of-substance fraction range from 5mol/mol to 50 %, in a matrix of nitrogen
or helium.
Laboratories that have an analytical system that is sensitive to the presence of
substantial levels of argon in such mixtures, can continue to use CCQM-K53 [1] to
underpin their CMCs. They can use this key comparison to underpin measurement
capabilities for determining the oxygen fraction in gas mixtures in nitrogen or helium
in the presence of argon.
CCQM K101
3
2. Participants
Participants are listed in table 1
Table 1 Participants
ACRONYM COUNTRY INSTITUTE
LNE France Laboratoire national de metrologie et d'essais
BAM Germany BAM Federal Institute for Materials Research and Testing
CERI Japan Chemicals Evaluation and Research Institute
NMIJ Japan National Metrology Institute of Japan
NIM China National Institute of Metrology
KRISS Korea Korea Research Institute of Standards and Science
VSL Netherlands Van Swinden Laboratory
VNIIM Russia D.I. Mendeleyev Institute for Metrology
SMU Slovak Slovak Institute of Metrology
NMISA South Africa National Metrology Institute of South Africa
NPL UK National Physical Laboratory
NIST USA National Institute of Standards and Technology
For details see internal measurement report section 9: Three gravimetrically prepared gas
mixtures with nominal values of 9, 7, and 11 ppm were used. Only in the latter 40 ppm Ar were
present.
Instrument calibration:
For details see internal measurement report sections 13, 9, and 11: The instrument was used in a
comparator mode. GLS regression technique according to ISO 6143:2001 was used to establish
the calibration function separately for each measurement campaign.
Samplingand handling:
For details see internal measurement report sections 4 and 5: The sample cylinder remained in
the laboratory for 19 days. Neither heating nor rolling was applied.
Uncertainty:
For details see internal measurement report sections 13,14, and 15.
Uncertainties related to balances and weights are covered by the Standard uncertainties of the
calibration gases used. Uncertainties of balances and weights in the preparation step of the
sample gas and those related to the cylinder of the sample gas have to be duly considered by the
organiser of the KC.
Uncertainty contributions considered in the measurement campaigns are the uncertainties of the
calibration gases used (specific for each gas), the stability of the Signals obtained for the
calibration gases and the sample (expressed as a Standard deviation of the mean of replicate
measurements), the resolution of the measurement device, and the contribution of the blank
(blank signal vs purity of the blank gas). Contributions are detailed in the table below.
The above-mentioned uncertainties have correspondingly been assigned to the mean values
obtained in the 5 measurement campaigns. GLS regression according to ISO 6143:2001 has been
applied to determine the analysis function(s) and value and uncertainty of the unknown. lh)s
technique strictly propagates all uncertainty contributions to the uncertainty of the unknown,
using the corresponding sensitivity coefficient for the uncertainty of each value.
Data have been submitted to GLS analysis both separately for each measurement campaign and
pooled for all five campaigns, as well as with and without including the blank. Although all four
assessment scenarios provide combined results fully compatible within the stated uncertainty,
pooling of all calibrations violates the limits of the quality parameters given in ISO 6143:2001
(SSD and GoF), meaning that calibrations are subject to a daily drift.
Calibrations treated separately fully comply with the QA requirements of ISO 6143:2001. Thus,
determinations obtained for the unknown in this approach were combined into the final result.
Notably, there was a fully negligible difference (with respect to the uncertainty stated) for
calibrations either including or not including the blank. The System is linear within the ränge
considered, and the estimates for the blank (blank signal vs purity of the blank gas) reasonable.
The uncertainty is dominated by the resolution of the measurement device and the blank. As the
individual uncertainty contributions are combined via GLS regression, the values given here will
not exactly amount to the combined uncertainty given.
Detailed uncertainty budget:
Typical evaluation of the measurement uncertainty ofO2
Quantity
(Uncertainty
source), X,
Gravimetric
values for
calibration gases
Signal stability
for calibration
gases and
sample
Resolution of
the
measurement
device
Blank
contribution
GLS
assessment
Estimate
~ 10.000
u.mol/m
ol
~ 10.000
Umol/m
ol
~ 10.00
u.mol/m
ol
0.2
u.mol/m
ol
-
Evaluatio
n type
(A or B)
A and B
combined
A
B
B
A
and B
Distrib
ution
normal
normal
rectan
gular
rectan
gular
as
listed
above
Standard
uncertainty
u(x-,)
0.015
u,mol/mol
0.02
umol/mol
0.05
u.mol/mol
0.1
umol/mol
-
Sensitivity
coefficient
1
1
1
1
MU
propagation
according to
ISO
6143:2001
Contribution
0.01
u.mol/mol
0.02
u.mol/m
ol
0.05
umol/rn
ol
0.1
u.mol/mol
at the
calibration
point of
Iowest
concentration
Report Form oxygen in nitrogen
Laboratory name: Chemicals Evaluation and Research Institute, Japan (CERI)
Cylinder number: FB-03506
Measurement 1#
Component Date
(dd/mm/yy)
Result
(mol/mol)
Standard deviation
(% relative)
Number of replicates
O2 29/1/2013 9.877 0.850 8
Measurement 2#
Component Date
(dd/mm/yy)
Result
(mol/mol)
Standard deviation
(% relative)
Number of replicates
O2 30/1/2013 9.863 0.544 8
Measurement 3#
Component Date
(dd/mm/yy)
Result
(mol/mol)
Standard deviation
(% relative)
Number of replicates
O2 31/1/2013 9.964 1.758 8
Measurement 4#
Component Date
(dd/mm/yy)
Result
(mol/mol)
Standard deviation
(% relative)
Number of replicates
O2 1/2/2013 9.966 0.776 8
Measurement 5#
Component Date
(dd/mm/yy)
Result
(mol/mol)
Standard deviation
(% relative)
Number of replicates
O2 5/2/2013 9.713 0.521 8
Measurement 6#
Component Date
(dd/mm/yy)
Result
(mol/mol)
Standard deviation
(% relative)
Number of replicates
O2 6/2/2013 9.724 0.838 8
Measurement 7#
Component Date
(dd/mm/yy)
Result
(mol/mol)
Standard deviation
(% relative)
Number of replicates
O2 7/2/2013 9.796 1.085 8
Measurement 8#
Component Date
(dd/mm/yy)
Result
(mol/mol)
Standard deviation
(% relative)
Number of replicates
O2 8/2/2013 9.826 0.757 8
Results
Component Result
(mol/mol)
Expanded uncertainty Coverage factor
O2 9.84 0.27 k=2
Details of the measurement method used:
Calibration standard:
Preparation method: Gravimetric method
Purity analyses
O2: NMIJ-CRM
N2: The purity is calculated as below.
Impurities in N2 are determined by analyses.
N
i
ipure xx1
1
where,
xi=mole fraction of impurity i
N=number of impurities
xpure=mole fraction purity of pure gas (N2)
The concentration of O2 in N2 was evaluated with instrument shown in Reference Method
Gas standard
Cylinder number Gravimetric concentration Expanded uncertainty(k=2)
CPB-21257 9.916 [mol/mol] 0.172 [mol/mol]
Reference Method:
Principle: GC-MS (Quadrupole)
Make: CANON ANELVA CORPORATION
Type: L-400G-GC
Data collection: L-400G-GC TRACEGAS ANALYZER AutoSampling Software
Measuring conditions
Carrier gas: Helium (20 mL/min)
Column: Molecular sieve 5A (60-80 mesh), 2 m×2.2 mm I.D.
Column temperature: 80 C
Sample loop: 1 mL
Sample handling:
A regulator with two gauges was attached to the cylinder. The output pressure of the regulator was
controlled at 0.1 MPa. The flow rate of sample gas was controlled at approximately 50 mL/min.
Measurement sequence:
R1→K1→R2→K2→R3→K3→R4→K4→R5…
Where
Ri: Measurement of gas standard (i=1-8)
Ki: Measurement of the K101 gas mixture (i=1-7)
Instrument calibration:
Mathematical model:
One-point calibration was used.
Detailed uncertainty budget:
Quantity
(Uncertainty
source), Xi
Estimate
xi
Evaluatio
n type
(A or B)
Distributi
on
Standard
uncertainty
u(xi)
Sensitivity
coefficient
ci
Contributio
n
u(yi)
Parent gas 0.15204
μmol/mol
B normal
0.07602
μmol/mol 1
0.07602
μmol/mol
Conc. of oxygen
in Nitrogen
0.02521
μmol/mol
A
- 0.02521
μmol/mol 1
0.02521
μmol/mol
Gravimetric
preparation of
gas standard
0.00078
μmol/mol
B
rectangle 0.00045
μmol/mol 1
0.00045
μmol/mol
Repeatability of
preparation
0.03077
μmol/mol
A -
0.03077
μmol/mol 1
0.03077
μmol/mol
Repeatability of
measurement
0.10108
μmol/mol
A -
0.10108
μmol/mol 1
0.10108
μmol/mol
Other Impurities
in nitrogen
negligible A - - -
Combined uncertainty: 0.1326 μmol/mol
Coverage factor: 2
Expanded uncertainty: 0.27 μmol/mol
Authors:
Dai Akima
Yukari Kawase
Shinji Uehara
Measurement report NMIJ
Measurement 1#
Component Date
(dd/mm/yy)
Result
(10-6 mol/mol)
Standard deviation
(% relative)
Number of
replicates
O2 02/04/2013 10.000 0.37% 4
Measurement 2#
Component Date
(dd/mm/yy)
Result
(10-6 mol/mol)
Standard deviation
(% relative)
Number of
replicates
O2 03/04/2013 9.918 0.44% 4
Measurement 3#
Component Date
(dd/mm/yy)
Result
(10-6 mol/mol)
Standard deviation
(% relative)
Number of
replicates
O2 04/04/2013 10.012 0.38% 4
Results
Component Result
(10-6 mol/mol)
Expanded uncertainty
(10-6 mol/mol) Coverage factor
O2 9.977 0.079 k = 2
Cylinder number of the sample : FB03058
Method description forms
Details of the measurement method used:
Reference Method:
Amount of substance of oxygen in the sample was determined by GC-TCD which has two ovens;
one is of Shimadzu GC-2014 and the other is an extra oven for low temperature. Volume of a
sample loop is 5 mL, and pressure in the loop was monitored by an absolute pressure transducer.
Temperature of the sample loop is thought to be constant because the loop is in the GC-2014
oven. A MS 5A column (2m; 60/80 mesh) in the GC 2014 oven (30 °C) separated Ar and O2 from
N2 which were not injected into MS 5A columns (2m X 3; 60/80 mesh) in cold oven (-15 °C) by
valve switching technique. The MS 5A columns (-15 °C) separate O2 from Ar, and they were
detected by the TCD. Current and temperature of the TCD were set to be 190 mA and 55 °C,
respectively. Pure He (Air Liquid Japan, alpha 2) was used as a carrier gas. Flow rate
(approximately 30 ml/min) of the carrier gas was controlled by automatic pressure controller.
The obtained peak areas were compensated by the pressure in the sample loop when the sample
was injected.
Calibration standard:
Four primary standard gas mixtures for calibration were prepared by mixing pure nitrogen and
oxygen by four steps of the gravimetric dilution method according to ISO 6142. The uncertainty
for the primary standard gas mixtures consists of uncertainties of weighing, amount of
substances of components in parent gases, and molar mass. Assigned values for the calibration
gases and their uncertainties are listed below.
Cylinde Number Component Assigned Value
(10-6 mol/mol)
Relative Standard
Uncertainty (%)
CPC00220 O2 8.0258 0.021
CPB32036 O2 9.0036 0.019
CPB32031 O2 9.9549 0.018
CPC00218 O2 10.9095 0.017
Results of impurity analysis of the pure oxygen and nitrogen gases are summarized below.
Oxygen in pure nitrogen was determined by APIMS.
Oxygen
Component Amount of substance
(10-6 mol/mol)
Standard Uncertainty
(10-6 mol/mol)
CH4 0.002 0.001
CO 0.007 0.004
CO2 0.052 0.001
Ar 0.09 0.05
N2 0.08 0.05
H2O 0.44 0.25
O2 999999.33 0.45
Nitrogen
Component Amount of substance
(10-6 mol/mol)
Standard Uncertainty
(10-6 mol/mol)
CH4 0.15 0.09
CO 0.44 0.26
CO2 0.16 0.09
Ar 0.50 0.29
O2 0.0025 0.0014
H2O 0.05 0.03
N2 999998.70 0.41
Instrument calibration:
The primary standard gas mixtures were used for the calibration of GC-TCD. Calibration curves
were obtained by Deming’s least squares method with a model “y = a + bx”. Variances of peak
areas to the primary standard mixtures and sample were thought to be the same.
The primary standard mixtures and the sample were measured four times. The order of the
measurement sequence was as follows: two or three of the primary standard mixtures sample
the rest of the primary standard mixtures. The obtained peak areas were corrected by the
pressure in the sample loop. There was no temperature correction because the sample loop
was in the GC oven in which the temperature was considered to be constant.
Sampling handing:
The sample cylinder was in a storage room (about 20 °C) after arrival. The cylinder was
stabilized to the room temperature (21 °C) before measurement. Flushing of a pressure
regulator was carried out with the sample or the primary standard gas mixtures at least 5 times.
The sample and the primary standard gas mixtures were transferred to the sample loop of GC by
mass flow controller (MFC), whose flow rate was set to be 75 sccm. The absolute pressure in
the sample loop was about 700 kPa.
Uncertainty:
a. Uncertainty related to the balance and weights; pooled uncertainty was used.
b. Uncertainty related to the gas cylinder; it was neglected.
c. Uncertainty related to the components gases; it was neglected.
d. Uncertainty related to the analysis; The uncertainty was estimated from the repeatability of
the peak areas for the calibration gases. The uncertainty related to the analysis was
reflected into the calibration curves.
Detailed uncertainty budget:
Typical evaluation of the measurement uncertainty of O2:
Quantity
(Uncertainty
source), Xi
Estimate
xi
Evaluation
type
(A or B)
Distributi
on
Standard
uncertainty
u(xi)
Sensitivity
coefficient
ci
Contribution
u(yi)
Standard gas
mixtures /
10-6 mol/mol
8 – 11 A Normal 0.02% 1 0.02%
Determination
by GC-TCD /
10-6 mol/mol
10 A Normal 0.4% 1 0.4%
1
CCQM-K101 Comparison Measurement report: Oxygen in Nitrogen Laboratory: National Institute of Metrology Cylinder number: FB03496
Measurement No. 1
Date
Result (µmol/mol)
Stand. deviation (µmol/mol)
number of sub- measurements
Oxygen
10/15/2013
10.026
0.027
3
Measurement No. 2
Date
Result (µmol/mol)
Stand. deviation (µmol/mol)
number of sub- measurements
Oxygen
10/16/2013
10.022
0.024
3
Measurement No. 3
Date
Result (µmol/mol)
Stand. deviation (µmol/mol)
number of sub- measurements
Oxygen
10/17/2013
10.028
0.022
3
Summary Results:
Gas mixture
Result
(assigned value) (µmol/mol)
Coverage
factor K
Assigned expanded
Uncertainty (µmol/mol)
Oxygen
10.025 ± 0.048
2
± 0.048
Reference Method: The oxygen was analyzed using a Delta-F 310ɛ analyzer. This analyzer utilizes an electrochemical cell and is capable of making oxygen measurements at the 10 nmol/mol level. Its upper range is 0-100 µmol/mol and does not over-range, and in order to display at nmol/mol resolution for the responding, a digital signal transfer was used to connect the Delta-F 310ɛ analyzer. A gas sampling
system was used to indicate a manual switchover from the NIM standard or CCQM cylinder to the Control cylinder (FB03513). The CCQM cylinder and the PRMs listed below were measured against the Control cylinder nine times during three different analytical periods. Calibration Standards: Three NIM’s gravimetrically prepared primary reference materials ranging in concentration from 9.5 µmol/mol to 10.0 µmol/mol oxygen/nitrogen were used in this analysis. The PRMs and their expanded uncertainties are listed below:
2
Cylinder Number Concentration (µmol/mol) Gravimetric Uncertainty (µmol/mol) FB03502 10.0253 0.0076 FB03487 9.9923 0.0081 CAL017807 9.5644 0.0085 These standards were prepared from different parent mixtures but all with the same source of balance gas (nitrogen) and component gas (oxygen). The table below gives an assay of the pure nitrogen and pure oxygen used to prepare these standards.
Component Purity of N2
(mol/mol)
Standard uncertainty
(mol/mol)
H2O 1.9E-08 1.0E-08
O2 1.40E-08 5.0E-10
H2 1.0E-07 1.0E-07
CO 2.0E-08 2.0E-08
CO2 1.0E-07 1.0E-07
CH4 1.0E-07 1.0E-07
Ar 4.9E-05 1.0E-06
N2 0.999951 1.02E-06
Component Purity of O2
(mol/mol)
Standard uncertainty
(mol/mol)
H2O 4.9E-09 5.0E-09
N2 3.0E-06 1.5E-06
H2 3.0E-07 1.5E-07
CO 2.0E-08 2.0E-08
CO2 5.0E-07 3.0E-07
CH4 1.0E-07 1.0E-07
Ar 2.0E-06 1.0E-06
O2 0.999994 1.84E-06 Instrument Calibration:
The Delta-F 310ɛ analyzer was calibrated using three gravimetrically prepared PRMs. The CCQM
sample (FB03496) was included in the analysis with the PRMs. They were all compared to the Control cylinder a minimum of two times during each of the three analytical days. The analytical scheme used for each primary standard and the CCQM cylinder on each analytical day was: Control cylinder PRM Standard (1st measurement) CCQM cylinder Control cylinder Control cylinder (2nd measurement) PRM Standard CCQM cylinder
3
Control cylinder Control cylinder (3rd measurement) PRM Standard CCQM cylinder Control cylinder Sample Handling: This analysis is to quantify the O2 in a single CCQM-K101 cylinder (FB03496). The sample was fitted with a low dead-volume, stainless steel regulator (no pressure gauges) with a CGA-590 fitting. Sample selection was achieved manually using a stainless steel six way valve and 1/8” stainless steel lines. The procedure called for each cylinder to have a 8.0 minutes period of equilibration and 3-minute data collection period. Uncertainty: PRM Validator is an ISO 6143-based spreadsheet that calculates the value-assignment and combined uncertainty using a suite of primary reference materials (PRMs), As uncertainty of CCQM sample, it incorporates the uncertainties in the gravimetric values of each PRM along with the standard deviation of the instrument measurement responses in different day’s measurements.
uv = ugrv2 + (
Sd′
n)2 + (
Sd′′
n)2
uv ---verification uncertainty ugrv---gravimetric uncertainty S
’d ---responses standard deviation in one day measurement
S’’d ---responses standard deviation in three days measurement
The coverage factor for the expanded uncertainty is 2.
a) Uncertainty Components for Analysis of Oxygen in CCQMK-101 Cylinder FB03496:
O2 was analysed using gas chromatography method. Instrument in use was GC Varian
equipped with Porapack and Molsieve packed columns, 2x 1mL sample loops, TCD detector.
Oven temperature was 40 °C, method time 9 min, carrier gas Helium. All measurements
were done in automatic way using selector gas valve. Before entering sample loops all gas
mixtures went through a mass flow controller and pressure controller for regulation.
Details of the measurement method used:
Measurement method with several automated runs was used. All runs in first, third, fifth
measurement sequence had rising molar fraction, second, fourth, sixth were processed in
reverse order. At least 3 calibration standards and sample were used at each automated run.
From each run was made one calibration curve with sample signals. Data were subjected to
the b_least program (weighted least square regression). The result of the measurement
sequence was the average of molar fractions.
All calibration standards were made gravimetrically according ISO 6142 and ISO 6143 in
SMU. Impurities in parent gases quality BIP plus- oxygen and nitrogen were analysed on GC
and FTIR. Content of oxygen impurity in nitrogen was measured using Trace oxygen analyzer
Teledyne 3000 TA –XL with the detection limit 0.01x10-6
mol/mol.
All cylinders were at SMU kept at 17 – 22 °C before measurement. Measuring cylinders were
equipped with pressure reducers. Sample was transferred to the instrument GC throw mass-
flow controller and pressure controller automatically in sequences.
Detailed uncertainty budget:
Uncertainty of instrument response consisted from figure characterized roughly immediate
repeatability and from signal drift estimated. From each run was made one calibration curve
with sample signals. These figures together with molar fraction data were subjected to b_least
program (weighted least square regression). Each run produced sample molar fraction with its
standard uncertainty. From all runs results = average of molar fractions in one sequence were
standard deviation found (uncertainty of type A) and from runs results uncertainties the mean
(through squares) was found (uncertainty of type B).
For each i-th
day the average xi was calculated (1). Standard uncertainty assigned to each i-th
day result (4) is from standard deviation of the average (2) and average from all b_least
uncertainties that day (3).
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n
xu
xu
nn
xx
xu
To estimate uncertainty from 3 days results we have kept “Standard Practice for Conducting
an Interlaboratory Study to Determine the Precision of a Test Method” (Annual Book of ASTM
Standards E 691-87) with some approximations.
)8(
)7(3
max
)6(
)(
)5(1
21
1
2
2
xxx
xs
p
xu
s
n
nsss
x
p
i
i
r
rxR
p – number of days (3)
n – number of measurements in 1 day
index i represents particular day
index j represents particular result (evaluated) from one calibration curve
Final result is average from 3 day results
)9(1
p
x
x
p
i
i
)10();max( Rr ssxu
Second part of final combined uncertainty is the standard uncertainty due to the calibration
standards derived from gravimetric preparation, impurity analysis and validation.
u(kal) is the uncertainty of PSM closest to the unknown sample
Estimation of the mole fraction component standard uncertainty measured sample is shown
in table number 1
Tab.1
Influence
parameter
Estimate Standard
uncertainty
Statistical
distribution
Sensitivity
coefficient
Contribution to
st.uncertainty
x 0.00000980
mol/mol
0.00000011
mol/mol
normal 1.0 0.00000011
xPSM 0.00000951
mol/mol
0.000000104
mol/mol
normal 1.0 0.000000104
together 0.00000015
Laboratory of gases optochemistry and CRM
Ing. Miroslava Valkova (SMU)
Measurement Report
CCQM-K101
Oxygen in Nitrogen at 10 mol/mol level
Laboratory name:National Metrology Institute of South Africa (NMISA)
Cylinder number: FB03494
Measurement 1#
Component Date
(dd/mm/yy)
Result
(mol/mol)
Standard
deviation
(% relative)
Number of
replicates
O2 21/01/2013 9,96 0,9 10
Measurement 2#
Component Date
(dd/mm/yy)
Result
(mol/mol)
Standard
deviation
(% relative)
Number of
replicates
O2 23/01/2013 9,79 1,3 10
Measurement 3#
Component Date
(dd/mm/yy)
Result
(mol/mol)
Standard
deviation
(% relative)
Number of
replicates
O2 06/02/2013 9,84 0,5 10
Result
Component Result
(mol/mol)
Expanded uncertainty
(mol/mol)
Coverage factor
O2 9,86 0,19 k =2
Details of the measurement method used:
Reference Method:
Gas Chromatographywith a Pulsed Discharged Helium Ionisation Detector (GC-PDHID)
Instruments:
The oxygen was analysed using a gas chromatograph equipped with a pulsed discharged helium ionisation
detector (GC-PDHID). The oxygen was separated from argon and nitrogen using a 30 m x 0,53 mm ID
capillary column (RT-MoleSieve 5Å), which was operated isothermally at 25 C with a carrier gas pressure of
450kPa helium. A 250 µℓ sample loop was used to inject the sample and the standard at the head of the
column. The PDHID-detector was operated at 100 C.
Calibration standards:
The primary standard gas mixtures (PSGMs) used for the calibration were prepared from pre-mixtures in
accordance with ISO 6142:2001 (Gas analysis - Preparation of calibration gas mixtures – Gravimetric method).
After preparation, the composition was verified using the method described in ISO 6143:2001. BIP Nitrogen
(6.0 quality), Oxygen (5.0 ultra-high pure) and Argon (5.0 quality) from Air Products, South Africa, were used to
prepare the PSGMs. The nitrogen impurities were below detection limits of the method.
Instrument calibration:
A set of five (5) PSMs of O2/Ar in nitrogen ranging from 8,0μmol/mol to 12,5 μmol/mol of oxygen and 81,0
μmol/mol to 20,4μmol/mol of argon were used to calibrate the Varian CP3800 GC-PDHID with a 250 µℓ
stainless steel sample loop, and a MoleSieve 5Å capillary column (30 m length, 0,53 mm internal diameter).
Certificate/Cylinder
number
O2
Gravimetric
concentration
(mol/mol)
O2
Standard
uncertainty
(mol/mol)
Ar
Gravimetric
concentration
(mol/mol)
Ar
Standard
uncertainty
(mol/mol)
NMISA20008335 8,0424 0,0056 20,4289 0,1122
NMISA20004937 9,0034 0,0062 30,5046 0,1161
NMISA20004909 10,0053 0,0069 40,7836 0,0618
NMISA3000543883 11,0049 0,0074 50,8556 0,1209
NMISA30008345 12,5020 0,0278 80,9690 6,4133
Sample handling:
After arrival, the cylinder was kept in the laboratory to stabilisein the laboratory environment. Each cylinder
(sample and standards) was equipped with a Tescom stainless steel pressure regulator that was adequately
purged. The sample flow rate was set at approx. 100 mℓ/min.
Uncertainty:
All measured certification data and calculations for the component concentrations of FB03494 have been
reviewed for sources of systematic and random errors. The review identified three sources of uncertainty whose
importance required quantification as estimated % relative uncertainties. These uncertainties are:
a) Gravimetric uncertainties of the PSGMs in the order of 0,07%.
b) Repeatability uncertainty (run-to-run) which ranged from 0,8 to 1,0% relative standard deviation.
c) Reproducibility uncertainty (day-to-day) which gives the % relative standard deviation represented in
the measurement report.
Detailed uncertainty budget:
The results for each day yielded an average concentration and a standard deviation. The average concentration
and ESDM were obtained by the method of bracketing.
The predicted concentrations for the sample for the three days were averaged, and a standard deviation
calculated for the three values. The uncertainties for the three different days and the verification uncertainty
(ESDM) were combined as shown in Equation 1:
2
2
3
2
2
2
12 )(3
ESDM
DayDayDayu
uuuu
c
………………..Equation 1
This combined standard uncertainty was converted to an expanded uncertainty by multiplying by a coverage
factor k = 2 as in Equation 2.
cukU , where k = 2. ...................................... Equation 2
Report Form: K101 - Oxygen in nitrogen
Laboratory: National Physical Laboratory
Cylinder Number: F803480
Measurement #1: GC-HDID
Component Date
(dd/mm/yy) Result (µmol/mol)
standard deviation
(µmol/mol)
No. of
replicates
O2 12/09/2013 9.946 0.007 4
Measurement#2 : GC-HDID
Component Date
(dd/mm/yy) Result (µmol/mol)
standard deviation
(µmol/mol)
No. of
replicates
O2 13/09/2013 9.953 0.021 4
Measurement#3 : GC-HDID
Component Date
(dd/mm/yy) Result (µmol/mol)
standard deviation
(µmol/mol)
No. of
replicates
O2 17/09/2013 9.954 0.016 4
Measurement#4 : CRDS
Component Date
(dd/mm/yy) Result (µmol/mol)
standard deviation
(µmol/mol)
No. of
replicates
O2 19/09/2013 9.950 0.034 2
Measurement#5: CRDS
Component Date
(dd/mm/yy) Result (µmol/mol)
standard deviation
(µmol/mol)
No. of
replicates
O2 19/09/2013 9.980 0.057 2
Final Result:
Component Date
(dd/mm/yy) Result (µmol/mol)
expanded uncertainty
(µmol/mol)
Coverage
Factor
O2 19/09/2013 9.96 0.08* 2
*The reported uncertainty is based on a standard uncertainty multiplied by a coverage factor k = 2, providing a
coverage probability of 95 %. Due to the presence of argon, the uncertainty is larger than would normally be
achieved for certifying a 10 µmol/mol O2/N2 mixture. Hence K101 should be considered as an analytical challenge
as opposed to a core comparison.
Details of the measurement method used
Reference method
The amount fraction of oxygen in the NIM mixture was measured using two methods. The first
involved a Cavity Ring Down Spectrometer (CRDS) and the second an Agilent-Technologies-7890A
Gas Chromatograph with a Helium Discharge Ionisation Detector (GC-HDID). The GC-HDID was set up
with a 50m-5A molecular sieve column.
Calibration standards
Two NPL Primary Standard Mixtures of nominally 10 µmol/mol oxygen in nitrogen were prepared in
accordance with ISO 6142. The purity of both source gases were analysed and each found to be
>99.9999 %. The mixtures were prepared in BOC 10 litre cylinders with Spectraseal passivation. The
schematic below shows the steps of oxygen dilution with nitrogen used in the gravimetric
preparation with nominal O2 amount fractions. Both were used in determining the amount fraction
of the NIM mixture.
Pure N6 O2
↓
1000 µmol/mol
↓
10 µmol/mol
Instrument calibration, data analysis and quantification
Reference mixtures were prepared with oxygen amount fractions that differed by less than 1% from
the nominal composition of the NIM mixture. This ensured that the uncertainty contribution from
any deviation from the linearity of the analyser response was negligible.
For GC-HDID analysis (measurements 1-3), the NPL reference standards and NIM mixture were
connected to a GC-HDID using purpose-built minimised dead volume connectors and 1/16 inch
Silcosteel tubing. Specialised NPL-designed flow restrictors were used to allow a stable sample flow
of 20 ml/min to be maintained throughout the analysis. The lines were thoroughly purged and flow
rates were allowed to stabilise before commencing. The oven was maintained at -60 °C by using
cryogenic cooling. The method was set up to alternate between the reference and NIM mixtures
using an automated switching valve. This method was repeated multiple times in order to obtain a
comprehensive data set. The detector responses were recorded as peak areas, and it was via the
comparison of the NPL and NIM mixture peak areas that the quantification of oxygen amount
fraction was achieved. A ratio of consecutive peak areas were taken to minimise the uncertainty
associated with detector drift.
For CRDS analysis (measurements 4-5), the CRDS analyser response to the matrix gas was recorded.
A comparison of the reference mixtures to the NIM mixture was achieved by measuring the analyser
response to the reference mixture for a twenty minute period followed by the NIM mixture for the
same time. At the end of the experiment the analyser response to the matrix gas was recorded a
second time. To minimise the effects from zero drift, a mean of the analyser response to the matrix
gas before and after the experiment was used. The amount fraction of oxygen in the NIM mixture
was determined using the amount fraction of the reference mixture and the ratio of the analyser
response to the reference and unknown mixtures. Samples were introduced into the CRDS at
approximately 4 bar using a low volume gas regulator.
Uncertainty
The amount fraction of oxygen in the NIM mixture, xc, was determined using the following
expression:
Where xr is the amount fraction of oxygen in the reference standard, yc, yr and yz are the analytical
responses obtained during measurements of the NIM mixture, the reference standard and zero
respectively. Both yc and yr are dominated by instrument repeatability. In the case of the GC analysis,
yz = 0. For the purposes of the uncertainty calculation, the equation above represents a situation
where repeatability of the measurement takes into account any drift over the measurement period.
The uncertainty in the amount fraction of oxygen in the NIM mixture was determined by adding the
four components in quadrature. The table which follows details the uncertainty analysis for an
example measurement using CRDS.
quantity unit example
value
standard
uncertainty
sensitivity coefficient
uncertainty
contribution
uncertainty type
distribution
xr µmol/mol 10.003 0.010 0.997 0.010 A normal
yz µmol/mol 0.014 0.020 -0.003 -5.7 x 10-5
A normal
yr µmol/mol 10.019 0.067 -0.997 -0.066 A normal
yc µmol/mol 9.991 0.052 1.000 0.052 A normal
xc µmol/mol 9.974
u(xc) µmol/mol 0.085
U(xc) µmol/mol 0.170
To obtain the final result for the comparison, an average was taken for the five measurements. The
following table shows the calculation of the final results and its uncertainty.
quantity unit example
value
standard
uncertainty
sensitivity coefficient
uncertainty
contribution
uncertainty type
distribution
x1 µmol/mol 9.946 0.075 0.200 0.015 A normal
x2 µmol/mol 9.954 0.076 0.200 0.015 A normal
x3 µmol/mol 9.953 0.080 0.200 0.016 A normal
x4 µmol/mol 9.950 0.085 0.200 0.017 A normal
x5 µmol/mol 9.980 0.087 0.200 0.017 A normal
r µmol/mol - 0.013 1.000 0.013 A normal
xf µmol/mol 9.96
u(xf) µmol/mol 0.04
U(xf) µmol/mol 0.08
Where x1-x5, r is a component from the reproducibility of the five separate measurements and xf is
the final value of the amount fraction of oxygen in the NIM mixture.
)(
)(
zr
zcr
cyy
yyxx
−
−
=
1
CCQM-K101 Comparison Measurement report: Oxygen in Nitrogen Laboratory: National Institute of Standards and Technology Cylinder number: FB03481
Measurement No. 1
Date
Result (µmol/mol)
Stand. deviation (µmol/mol)
number of sub- measurements
Oxygen
2/7/2013
9.919
0.025
3
Measurement No. 2
Date
Result (µmol/mol)
Stand. deviation (µmol/mol)
number of sub- measurements
Oxygen
2/8/2013
9.916
0.015
3
Measurement No. 3
Date
Result (µmol/mol)
Stand. deviation (µmol/mol)
number of sub- measurements
Oxygen
2/14/2013
9.901
0.017
3
Summary Results:
Gas mixture
result (assigned value) (µmol/mol)
Coverage factor
Assigned expanded Uncertainty (%)
Oxygen
9.912 ± 0.048
2
± 0.48
Reference Method: The oxygen was analyzed using a Delta-F Nanotrace II™ analyzer (NIST# 592249). This analyzer utilizes an electrochemical cell and is capable of making oxygen measurements at the nmol/mol level. Its upper range is 0-10 µmol/mol and does not over-range. A computer-operated gas sampling system (COGAS #15) was used to audibly indicate a manual switchover from the NIST standard or CCQM cylinder to the Control cylinder (CC336387). The CCQM cylinder and the PSMs listed below were measured against the Control cylinder nine times during three different analytical periods. Calibration Standards: Five NIST gravimetrically prepared primary reference materials ranging in concentration from 3.7 µmol/mol to 9.8 µmol/mol oxygen/nitrogen were used in this analysis. The PSMs and their expanded uncertainties are listed below:
2
Cylinder Number Concentration (µmol/mol) Uncertainty (µmol/mol) FF17720 3.6665 0.0019 FF17691 5.4678 0.0021 FF17703 7.3199 0.0023 FF17699 9.0634 0.0019 FF17692 9.8402 0.0020 These standards were prepared from different parent mixtures but all with the same source of balance gas (nitrogen). The table below gives an assay of the nitrogen used to prepare these standards. Mole fraction Uncertainty Component µmol/mol µmol/mol Oxygen 0.003 0.001 Argon 97 5 Moisture 0.06 0.02 Nitrogen (Difference) 999902.9 5.0 Instrument Calibration: The Delta-F Nanotrace II™ analyzer was calibrated using these five gravimetrically prepared PSMs. The CCQM sample (FB03481) was included in the analysis with the PSMs. They were all compared to the Control cylinder a minimum of three times during each of the three analytical days. The analytical scheme used for each primary standard (or the CCQM cylinder) on each analytical day was: Control cylinder PSM Standard (1st measurement) Control cylinder PSM Standard (2nd measurement) Control cylinder PSM Standard (3rd measurement) Control cylinder Sample Handling: This analysis is to quantify the O2 in a single CCQM-K101 cylinder (FB03481). The sample was fitted with a low dead-volume, stainless steel regulator (no pressure gauges) with a CGA-590 fitting. Sample selection was achieved manually using a stainless steel three way valve and 1/8” stainless steel lines. The computer operated gas analysis system (COGAS #15) was used as an audible cue to manually switch the three way valve from Control cylinder position to the respective NIST standard or CCQM cylinder. Prior to starting each set of analyses the regulator was flushed five times. The output pressure of each regulator was set to 25psig (using an exterior Heise gauge) and the needle valve was adjusted to provide 1.0L sample flow to the instrument and 0.2L bypass flow. The procedure called for each cylinder to have a 4.0 minutes period of equilibration and two-minute data collection period. Due to the time required to completely purge the sample lines, each analytical measurement was repeated and the instrument response for this second measurement was used to calculate the CCQM cylinder’s concentration. Uncertainty: PSM Validator is an ISO 6143-based spreadsheet that calculates the value-assignment and combined uncertainty using a suite of primary standard materials (PSMs), a Control cylinder and the CCQM sample. It incorporates the uncertainties in the gravimetric values of each PSM along with the imprecision of the instrument measurement responses.
3
The coverage factor for the expanded uncertainty is 2.
a) Uncertainty Components for Analysis of Oxygen in CCQMK-101 Cylinder FB03481: