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Metrology Infrastructurein Gas Analysis

Ed W.B. de Leer

NMi Van Swinden Laboratorium

MiC Symposium, Beijing 18-22 October 2004

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Importance of Gas Analysis

Economic Value• Natural Gas (calorific value)• Chemical process industry (ethylene,etc.)• Electronic industry (reactive gases, H2O)• Food industry and health care (purity, composition)

Environmental regulations• Industrial stack emissions (NOx, SO2, HCl, etc.)• Automotive gases (CO, CO2, C3H8, NO)• Occupational hygiene (VOC, particles)• Ambient air quality (Benzene, O3, CH4, N2O, VOC,

etc.)

Legislation• Breath Analysis (ethanol)• Odor Control (n-butanol)

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Traceability to SI ISO TC 158

Laboratory Accreditation

Infrastructure for Gas Analysis

Instrument Manufacturers Reference Gas Producers

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Start of Traceability Chain (I)

For static gas mixtures, the traceability chain starts with a primary realisation of the definition of the mole fraction or amount of substance fraction for a specified chemical entity.

nB = amount of substance of entity B

i

iB

B

i

BB

Mm

M

m

n

ny

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Primary Realisation of mol/mol

A primary realisation (PSM) of the amount fraction in a static gas mixture involves (ISO 6142:2001):

accurate weighing (incl. buoyancy correction) of pure parent gases (or liquids) in a clean high pressure cylinder (uc ≈ 0.001-0.1%)

Impurity analysis of the parent gases/liquids

Analytical verification of the composition against a coherent set of primary standards (uc ≈ 0.05-1%)

Stability testing

Problems: low amount fractions (nmol/mol) for reactive gases, sorption on cylinder wall, isotopic variation, phase separation

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Stability of PSMs

Stability 600 mmol/mol NO in N2

-0,2

-0,1

0

0,1

0,2

0,3

0 5 10 15

Time (0,5 a)

%

av= +0.004 s.d. = 0.105

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Start of Traceability Chain (II)

For dynamically generated gas mixtures, the traceability chain starts with a primary realisation for amount concentration (mol/m3) for a specified chemical entity.

B

BBB VM

m

V

nc

N.B. Pressure and temperature need to be defined as well!

Usually, permeation, diffusion or injection of a pure gas in a flowing gas stream produces the primary realisation.

Key Comparison of National Standards

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Experimental Set-up KCs (I)

Pilot NMI Participating NMI

Pure gases

PRM

gravimetry

Pure gases*

PSM*comparison

secondary methods(NDIR, GC, FTIR, ….)

gravimetry

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CCQM-K3 – Automotive gases

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CCQM-K4 Ethanol in air

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CCQM GAWG Key Comparisons

Key comparison identifier

Description Status Pilot

CCQM-K1aCCQM-K1bCCQM-K1cCCQM-K1dCCQM-K1eCCQM-K1fCCQM-K1gCCQM-K3CCQM-K4CCQM-K7CCQM-K10

CO in nitrogen (3 concentrations)CO2 in nitrogen (3 concentrations)NO in nitrogen (2 concentrations)SO2 in nitrogen (2 concentrations)Natural gas Type INatural gas Type IINatural gas Type IIIAutomotive gases (CO, CO2, C3H8)Ethanol in airBTEX in air (50 nmol/mol)BTEX in air (5 nmol/mol)

In KCDBIn KCDBIn KCDBIn KCDBIn KCDBIn KCDBIn KCDBIn KCDBIn KCDBIn KCDBIn KCDB

NMi VSLNMi VSLNMi VSLNMi VSLNMi VSLNMi VSLNMi VSLNMi VSLNPLNISTNIST

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CCQM GAWG Key comparisons (II)

Key comparison identifier

Description Status Pilot

CCQM-K15CCQM-K16aCCQM-K16bCCQM-K22CCQM-K23CCQM-K26aCCQM-K26bCCQM-K41CCQM-K46CCQM-K51CCQM-K52CCQM-K53CCQM-Kxx

SF6 and CF4 in nitrogenNatural gas Type IVNatural gas Type VVOC in airNatural gas K1e,f,g repeatNO in nitrogen (ambient level)SO2 in nitrogen (ambient level)H2S in air/nitrogenNH3 in nitrogen

CO in nitrogen (5μmol/mol)CO2 in air (380-400 μmol/mol)Preparative capabilities (O2 in N2)Prep. Capabilities (n-hexane in CH4)

CompletedIn KCDBIn KCDBDraft BDraft ADraft ADraft ADraft APlannedPlannedPlannedPlannedPlanned

KRISSNMi VSLNMi VSLNMIJNMi VSLNPLNPLNISTNMi VSLCSIR-NMLNMi VSLKRISSNMi VSL

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New Set-up CCQM-P23

Pilot NMI Participating NMIs

Pure gases

Series of PRMs

GravimetryAnalytical comparison under repeatabilty

conditions

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“High Accuracy” comparisons

All laboratories send a standard to the pilot laboratory

Preparation errors can now be Preparation errors can now be “randomised”“randomised”

Author: Martin Milton

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Gravimetry: 1000 mol/mol CO

1000 mmol/mol CO in Nitrogen

8100

8200

8300

8400

8500

8600

8700

8800

8900

940 960 980 1000 1020 1040 1060

grav. mol fraction (mmol/mol)

Co

rrec

ted

res

po

nse

(m

V)

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CCQM-P23

• CCQM-P23 used mixtures of CO/N2 at three amount fractions 50,000 1,000 and 10 mmol/mol.

• In the first phase these were all analysed by NDIR at NMi (The Netherlands)

• Evidence was found for 13C/12C variations in pure CO and for an influence of the 13C/12C ratio on the NDIR signal. Extreme outliers from KRISS (Korea) and NIST (USA)

• In the second phase two sets of mixtures were re-analysed:– 50,000 mmol/mol by NIST (USA) using GC/TCD – 1,000 mmol/mol by Metas (Switzerland) using GC/FID

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GC-TCD results

GC-TCD Results for 50,000 umol/mol CO in nitrogen

0,93

0,94

0,95

0,96

0,97

0,98

0,99

1,00

1,01

1,02

1,03

47000 47500 48000 48500 49000 49500 50000 50500 51000 51500 52000 52500

Concentration (umol/mol)

Rat

io t

o C

on

tro

l

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GLS for GC-TCD versus Gravimetry

• Conclusions for 50,000 mmol/mol– Std dev of residuals is 1mmol/mol (0.002% rel)-

after excluding two outliers– At 50,000 mmol/mol, the gravimetric values are

very consistent within their stated uncertainties.

-80

-60

-40

-20

0

20

40

60

BAM CENAM CSIRO IPQ KRISS LNE NIST NMIJ NPL

Re

sd

iua

l De

via

tio

n (

um

ol/m

ol)

k=2k=2

Author: Martin Milton

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GLS for 1,000 mmol/mol

• Conclusions– Std dev of residuals is 1.7 mmol/mol (0.17%relative)– At 1,000 mmol/mol , five (out of nine) of the gravimetric

values are not consistent within their stated uncertainties.

-4

-2

0

2

4

6

8

BAM LNE SMIJ NPL IPQ KRISS NIST Metas CSIRO

Resid

ual

Devia

tio

n (

um

ol/

mo

l)

k=2k=2

Author: Martin Milton

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Greenhouse gases: CH4

Author: Adriaan van der Veen

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GLS for CH4 Greenhouse gas

Conclusion:

The std dev of residuals in x-direction is 0.012 μmol/mol (0.6% rel)The uncertainty of two gravimetric standards is not compliant with the regression

Residuals (x-direction)

-0.060

-0.040

-0.020

0.000

0.020

0.040

0.060

1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2

amount-of-substance fraction (µmol/mol)

Resid

ual (x

, µ

mol/m

ol)

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CCQM GAWG Pilot Studies

Key comparison identifier

Description Status Pilot

CCQM-P23

CCQM-P24CCQM-P28CCQM-P41

CCQM-P51CCQM-P71CCQM-P87

Gravimetry (CO, 3 amount fractions) + additional studiesDynamic mixing of gasesAmbient ozone concentrationsGreenhouse gases (CO2 and CH4)Analysis and gravimetryCF4 and SF6 in nitrogenVOC’s in nitrogenGravimetry (natural gas)

Completed

In progressDraft BCompleted

CompletedDraft BPlanned

NMi, NPL, NIST, KRISSLNEBIPMNMi VSL

KRISSNMIJNPL

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Gas CMCs in KCDB

12

480

33

13

3

13

0 100 200 300 400 500 600

4.1 High purity

4.2 Environmental

4.3 Fuel

4.4 Forensic

4.5 Medical

4.6 OthersAugust 9, 2004

18 Countries554 CMC entries146 Measurands 12 Gas Matrices

August 9, 2004

18 Countries554 CMC entries146 Measurands 12 Gas Matrices

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Function of NMI gas Standards

Primary realization of gas composition standards

Production of traceable gas transfer standards

Calibration of secondary gas standards, instruments, etc

Production of pure gases

Cylinder treatment

Production of traceable calibration gases for field applications

NMI

Industry

Workfloor applications in gas analysis

e.g. testing automotive exhaust gases, natural gas composition

SI traceable measurement results

Workfloor

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Accreditation of Gas RM Producers

• Accredited as Calibration Laboratory (ISO/IEC 17025)– Belgium (1) France (2, incl. LNE)– Germany (2) Italy (2)– Netherlands (2, incl. NMi) Spain (6)– Sweden (1) Switzerland (3)– United Kingdom (7, incl. NPL)

• Accredited as Test Laboratory (ISO/IEC 17025)– Mexico (1)

• Accredited as Reference Material Producer (ISO Guide 34)– Australia (2) Japan (2, incl. NMIJ)

• Accredited by Jcss Japan (3)• Legal Metrology Systems e.g. China, Russia

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Standardisation

• ISO/TC 146 Air Quality

• ISO/TC 158 Gas Analysis

• ISO/TC 193 Natural Gas

• ISO/TAG 4 Metrological Issues

• OIML Recommendations

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Conclusion

• The metrological concepts of traceability and measurement uncertainty are widely accepted in the field of gas analysis

• Cooperation between NMI’s, Standardization bodies, and Industry is essential for continued development