AFRIMETS.QM-K27 DETERMINATION OF ETHANOL IN AQUEOUS

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AFRIMETS.QM-K27

DETERMINATION OF ETHANOL IN AQUEOUS MATRIX

FINAL REPORT

January 2013

COORDINATING LABORATORY

National Metrology Institute of South Africa (NMISA)

AFRIMETS.QM-K27 Determination of ethanol in aqueous matrix

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AFRIMETS.QM‐K27 Study: Determination of Ethanol in Aqueous Matrix

Marcellé Archer, Maria Fernandes-Whaley, Ria Visser, Jayne de Vos, Sara Prins National Metrology Institute of South Africa (NMISA) Pretoria, South Africa Adriana Rosso and Mariana Ruiz de Arechavaleta Instituto Nacional de Tecnologia Industrial (INTI) Buenos Aires, Argentina Ibrahim Tahoun National Institute for Standards (NIS) Giza, Egypt Elias Kakoulides National Reference Laboratory in Chemical Metrology (E.XH.M) Athens, Greece Caleb Luvonga and Geoffrey Muriira Kenya Bureau of Standards (KEBS) Nairobi, Kenya Evaldas Naujalis State Research Institute Centre for Physical Sciences and Technology (VMT/FTMC) Vilnius, Lithuania Osman Bin Zakaria National Metrology Laboratory (SIRIM) Sepang, Malaysia Mirella Buzoianu National Institute of Metrology (INM) Bucharest, Romania Jelena Bebić Directorate of Measures and Precious Metals (DMDM) Belgrade, Serbia Ben Achour Mounir National Institute of Research and Physical and Chemical Analysis (INRAP) Arania, Tunisia Ngo Huy Thanh Vietnam Metrology Institute (VMI) Hanoi City, Vietnam


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TABLE OF CONTENTS

Abbreviations ....................................................................................................................... 5 Introduction .......................................................................................................................... 6 Participants .......................................................................................................................... 7 Materials .............................................................................................................................. 7 Measurement protocol ......................................................................................................... 8 Key comparison reference value ......................................................................................... 9 Schedule .............................................................................................................................. 9 Measurement equation for assigned reference value ........................................................ 10 Uncertainty evaluation of the assigned reference value .................................................... 10 Measurement methods ...................................................................................................... 10 Results ............................................................................................................................... 10 Sources of uncertainty ....................................................................................................... 18 Discussion of results .......................................................................................................... 27 Supported CMC claims ...................................................................................................... 28 Conclusions ....................................................................................................................... 28 References ......................................................................................................................... 30 Coordinator ........................................................................................................................ 30 Appendix 1- Degrees of equivalence ................................................................................. 31 Appendix 2- Standard deviation for proficiency assessment ............................................. 37 Tables and figures

Table 1 Summary of CCQM OAWG key comparison K27 series ........................................ 6 Table 2 AFRIMETS.QM-K27 participants ............................................................................ 7 Table 3 Preparation of solutions .......................................................................................... 8 Table 4 AFRIMETS.QM-K27 Schedule ............................................................................... 9 Table 5 Analytical instruments and traceability standards used by participants ................ 11 Table 6 Results for Level 1 ................................................................................................ 12 Table 7 Results for Level 2 ................................................................................................ 13 Table 8 Sources of uncertainty .......................................................................................... 18 Table A1 Degrees of equivalence for Level 1 .................................................................... 32 Table A2 Degrees of equivalence for Level 2 .................................................................... 33 Table A3 Relative degrees of equivalence for CCQM-K27a/ b, CCQM-K27.1, CCQM-K27.2 and AFRIMETS.QM-K27 and associated relative expanded uncertainty ............................................................................ 35


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Figure 1 Mean results for each participant for Level 1 (standard uncertainty) ............... 14 Figure 2 Mean results for each participant for Level 1 (expanded uncertainty) ............. 15 Figure 3 Mean results for each participant for Level 2 (standard uncertainty) ............... 16 Figure 4 Mean results for each participant for Level 2 (expanded uncertainty) ............. 17 Figure 5 Percentage differences from the assigned reference value for the

AFRIMETS.QM-K27 study ..…………………………………..………….………..27 Figure 6 Percentage differences of the results from the KCRV or assigned

reference value for CCQM-K27a, CCQM-K27.1, CCQM-K27.2 and AFRIMETS.QM-27……………………………………………………..……………29

Figure A1 Degrees of equivalence for Level 1 ................................................................. 34 Figure A2 Degrees of equivalence for Level 2 ................................................................. 34 Figure A3 Relative DoE for CCQM-K27a/ b, CCQM-K27.1, CQM-K27.2 and

AFRIMETS.QM-K27 ........................................................................................ 36 Figure A4 Comparison of CCQM-K27a and participant uncertainties, Level 1 ................ 38 Figure A5 Comparison of CCQM-K27a and participant uncertainties, Level 2 ................ 39 Figure A6 Comparison of Horwitz and NMISA study uncertainties, Level 1 .................... 40 Figure A7 Comparison of Horwitz and NMISA study uncertainties, Level 2 .................... 40


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ABBREVIATIONS

AFRIMETS Intra-Africa Metrology system APMP Asia Pacific Metrology Programme BIPM International bureau of weights and measures CCQM Consultative committee for amount of substance CMC Calibration and measurement capability DI Designated institute EURAMET European Association of National Metrology Institutes FID Flame ionisation detector GC Gas chromatography GC-ID-MS Gas chromatography-isotope dilution-mass spectrometry KCDB Key comparison database NMI National metrology institute OAWG Organic analysis working group RMO Regional metrology institute SIM Interamerican metrology system TOFMS Time-of-flight mass spectrometry


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INTRODUCTION

The accurate determination of ethanol content in aqueous medium is critical for regulatory

forensic and trade purposes. For forensic purposes, ethanol is determined for the effective

regulation of blood alcohol levels (e.g., driving under the influence of alcohol, autopsies,

etc.). As a trading commodity, ethanol content is determined for the classification, control

and taxation of alcoholic beverages.

The CCQM Organic Analysis Working Group has carried out several key comparisons on

the determination of ethanol in wine and aqueous matrices, these are summarised in Table

1. Reports on these comparison results can be downloaded from the BIPM KCDB website

[1].

Table 1: Summary of CCQM OAWG key comparison K27 series

Year Comparison Description

2002 CCQM-K27a Forensic aqueous ethanol [1]

2002 CCQM-K27b Ethanol in wine as commodity [2]

2003 CCQM-K27.1 Subsequent forensic aqueous ethanol [3]

2006 CCQM-K27.2 Subsequent forensic aqueous ethanol [4]

The CCQM-K27 comparison series has demonstrated international measurement

comparability between NMIs for the determination of this much traded and forensically

important compound. In addition, the type B key comparison CCQM-K79 (2010) compared

aqueous ethanol certified reference material (CRM) solutions produced and assayed by

various NMIs [5]. The CCQM-K79 comparison also supports capabilities demonstrated in the

CCQM-K27 comparison series.

Within the AFRIMETS RMO, certain NMIs/ DIs have indicated the need to demonstrate their

measurement capability for the determination of ethanol in aqueous matrices. AFRIMETS

therefore conducted a regional key comparison which was also open to interested

international NMIs.

The National Metrology Institute of South Africa (NMISA) coordinated this comparison. The

NMISA has demonstrated its capability in CCQM-K27.1, CCQM-K27.2 and CCQM-K79, and


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is an accredited CRM producer for aqueous ethanol solutions. The NMISA currently has

calibration and measurement capabilities (CMCs) in the BIPM Key Comparison Database

(KCDB) for the determination of aqueous ethanol solutions.

PARTICIPANTS

Table 2 lists the participants, institute and RMO, for this comparison.

Table 2: AFRIMETS.QM-K27 Participants

Abbreviation Institute Country RMO

INTI Instituto Nacional de Technologia Industrial Argentina SIM

NIS National Institute for Standards Egypt AFRIMETS

E.XH.M-GCSL/EIM

National Reference Laboratory in Chemical Metrology Greece EURAMET

KEBS Kenya Bureau of Standards Kenya AFRIMETS

VMT/FTMC State Research Institute Center for Physical Sciences and Technology

Lithuania EURAMET

NML-SIRIM National Metrology Laboratory Malaysia APMP

INM National Institute of Metrology Romania EURAMET

DMDM Directorate of Measures and Precious Metals Serbia EURAMET

INRAP Institut National de Recherche et d’Analyse Physico-Chimique

Tunisia AFRIMETS

VMI Vietnam Metrology Institute Vietnam APMP

MATERIALS

Two solutions of ethanol in water were gravimetrically prepared by mixing known masses of

pure water and ethanol. The purity of the ethanol used to prepare the samples was

assessed by headspace GC-FID and on-column direct injection GC-FID, on two different

stationary phases. Potential impurities were also screened for by GC-TOFMS. Karl Fischer

coulometric titration was used to assess the water content.

The solutions were bottled into 25 ml glass containers and sealed. There were 64 bottles in

each batch. The concentrations were then confirmed by titrimetric analysis of eight bottles


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from each batch, selected by taking the first and every eighth bottle from each batch. The

results obtained are given in Table 3. The analysis confirmed the concentration and

homogeneity of the samples and the assigned value was based on the purity-corrected

gravimetric preparation and titrimetric homogeneity.

Table 3: Preparation of solutions

Gravimetric

concentration

(mg/g)

Mean titrimetric

concentration

(mg/g)

Between-bottle

homogeneity

(%RSD)

Assigned

concentration

(mg/g)

0,3249 ± 0,0002 0,3273 ± 0,0023 0,32 0,3249 ± 0,0021

4,6649 ± 0,0028 4,6769 ± 0,0180 0,16 4,6649 ± 0,0152

Similar solutions were found to be stable for at least 24 months after bottling. The stability

was tested at storage conditions as well as expected shipping conditions (up to 35ºC).

MEASUREMENT PROTOCOL

DESCRIPTION OF MATERIALS

Each participant received two 25 ml bottles of aqueous ethanol solutions at each concentration

level, i.e., four bottles in total. The study consisted of two different concentrations of aqueous

ethanol solution, viz 0,3249 ± 0,0021 mg/g and 4,6649 ± 0,0152 mg/g.

STORAGE OF MATERIALS

The samples should have been stored at temperatures between +2°C and +8°C after

receipt. They should have been allowed to reach room temperature prior to analysis.

INSTRUCTIONS FOR USE

Participants were required to analyse duplicate sub-samples from each of the two bottles at

each level. Sub-samples could be taken from the bottle at different times, provided that

precautions were taken to prevent undue evaporation (having the bottle open for a minimum

amount of time, closing it securely and storing it appropriately). It was not recommended that

the sample be transferred to another bottle before use.


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REPORTING OF RESULTS

Participants were requested to determine the mass fraction (mg/g) of ethanol in the two

samples.

An electronic result sheet was distributed to the participants. Analytical results that were to

be reported include:

(i) mass fraction of ethanol in mg/g;

(ii) detailed technical information describing the methodology used;

(iii) the source and purity of any reference and/or standard materials used;

(iv) and a full measurement uncertainty budget (including all potential uncertainty

components for the measurand; combined standard uncertainty; expanded uncertainty

and the coverage factor).

KEY COMPARISON REFERENCE VALUE (KCRV)

According to the CIPM MRA document concerning measurement comparisons, only CIPM

key comparisons, i.e., those performed by Consultative Committees or the BIPM, may have

a KCRV. Key comparisons performed by regional metrology organizations (RMOs) link to

the KCRV through reference to the results from those institutes which have also taken part in

the CIPM key comparison [6]. The assigned reference value of the aqueous ethanol

solutions will be used to link AFRIMETS.QM-K27 to the CCQM-K27 comparison KCRV. The

assigned reference values for AFRIMETS.QM-K27 are the assigned concentrations (mg/g)

listed in Table 3. NMISA’s capability to gravimetrically prepare ethanol solutions was

demonstrated in CCQM K79 [5].

SCHEDULE

Table 4: AFRIMETS.QM-K27 Schedule

Call for participation June 2011

Registration deadline 30th June 2011

Sample distribution End July 2011

Data due to coordinator 15th September 2011 extended to 23rd September 2011

Initial report of results October 2011

Discussion of results

October 2011,

November 2011 CCQM OAWG meeting


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MEASUREMENT EQUATION FOR ASSIGNED REFERENCE VALUE

The assigned reference value was based on the gravimetric preparation of the solutions

using Equation 1.

∗ ∗

/ [Eqn. 1]

where the masses are given in grams.

UNCERTAINTY EVALUATION OF THE ASSIGNED REFERENCE VALUE

The standard uncertainty was evaluated from Equation 2.

∗

/

[Eqn. 2] where the homogeneity is the between-bottle homogeneity as determined titrimetrically.

The expanded uncertainty at approximately 95% level of confidence was assigned from Equation 3.

∗ / [Eqn. 3] where U is the expanded uncertainty, u is the standard uncertainty and k is the coverage factor; k =2.

MEASUREMENT METHODS

The analytical instrumentation, traceability and quantification used by each participant is

summarized in Table 5. All participants established traceability through in-house certified

reference materials or through certified reference materials from other NMIs.

RESULTS

The results are tabulated in Table 6 for Level 1 and in Table 7 for Level 2. The mean results

for each participant are plotted in Figures 1 to 4. The uncertainty bars in Figures 1 and 3

represent the standard uncertainty (k = 1) reported by each laboratory. The uncertainty bars

in Figures 2 and 4 represent the expanded uncertainty reported by each laboratory. The

titrimetric results from NMISA are included for reference.


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Table 5: Analytical instruments and traceability standards used by participants

Institute Instrumentation Traceability standards Quantification

INTI GC-FID, with a DB Wax capillary column

In-house reference materials verified by NIST SRM 1847

10–point calibration curve with methyl ethyl ketone internal standard

NIS Headspace GC-FID, with a DB Wax capillary column

NIS certified aqueous ethanol solutions

5-Point calibration curve with 1-propanol internal standard

E.XH.M GC-FID and GC-IT-MS, with Porabond-Q capillary column

NIST SRM 2896 Exact matching GC-ID-MS

KEBS GC-FID, with a Varian CP-Sil 5 CB capillary column

NIST SRM 1828b (six levels)

5-Point calibration curve with 1-propanol internal standard

VMT/FCMT GC-FID, with a DB Wax capillary column

ERM-AC510a and ERM-AC403d

Bracketing

NML-SIRIM GC-FID, with a TR Wax 230810 capillary column

NIST ethanol CRM 7-point calibration curve followed by exact matching GC-MS with 1-propanol as internal standard

INM Titrimetry NIST SRM 136f potassium dichromate

Oxidation of ethanol, followed by back-titration of potassium dichromate by sodium thiosulphate

DMDM GC-MS and GC-FID LNE aqueous ethanol solution

GC-FID with 5-point calibration curve

INRAP Headspace GC, with HP Innowax PEG capillary column

NMISA aqueous ethanol CRMs

6-Point calibration curve with acetonitrile internal standard

VMI Titrimetry Oxidation of ethanol, followed by back-titration of potassium dichromate by sodium thiosulphate

NMISA Titrimetry ERM AC402b & ERM AC409a

Oxidation of ethanol, followed by back-titration of potassium dichromate by iron ammonium sulphate

AFRIMETS.QM-K27 Determination of ethanol in aqueous media

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Table 6: Results for Level 1

Institute

Ethanol mass fraction (mg/g)

Mean CV (%) Standard

uncertainty (mg/g)

Expanded uncertainty

(mg/g)

Coverage factor k

Bottle 1 Bottle 2

INTI 0,3268 0,3279

0,3308 0,3317

0,3293 0,7061 0,0026 0,0052 2

NIS 0,3327 0,3312 0,3320 0,3195 0,003 0,006 2

E.XH.M 0,3306 0,3299 0,3303 0,1499 0,0020 0,0040 2

KEBS 0,2995 0,3037 0,3016 0,9847 0,0008 0,0016 2

VMT/FTMC 0,306 0,305 0,306 0,231 0,003 0,006 2

NML-SIRIM 0,31 0,31 0,31 0,0 0,005 0,01 2

INM 0,203 0,228

0,266 0,283

0,245 14,788 0,0085 0,017 2

DMDM 0,3663 0,36072 0,3635 1,0854 0,0028 0,0057 2

INRAP 0,308 0,333 0,321 5,516 0,008 0,016 2

VMI 0,324 0,322 0,323 0,438 0,002 0,004 2,14

NMISA 0,3273* 0,322 (n = 8) 0,0012 0,0023 2

* mean of titrations of aliquots from eight separate bottles


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Table 7: Results for Level 2

Institute

Ethanol mass fraction (mg/g)

Mean CV (%) Standard

uncertainty (mg/g)

Expanded uncertainty

(mg/g)

Coverage factor k

Bottle 1 Bottle 2

INTI 4,631 4,638

4,694 4,684

4,662 0,683 0,036 0,072 2

NIS 4,671 4,668 4,670 0,045 0,017 0,034 2

E.XH.M 4,754 4,789 4,772 0,519 0,0266 0,0533 2

KEBS 4,7880 4,7172 4,7526 1,0534 0,0119 0,0239 2

VMT/FTMC 4,51 4,47 4,49 0,630 0,04 0,08 2

NML-SIRIM 4,69 4,69 4,69 0,0 0,03 0,06 2

INM 4,62 4,48

4,55 4,71

4,59 2,14 0,07 0,14 2

DMDM 5,01193 5,00788 5,00991 0,05716 0,022 0,045 2

INRAP 4,179 4,270 4,22 1,52 0,013 0,026 2

VMI 4,665 4,663 4,664 0,030 0,021 0,045 2,2

NMISA 4,6749* 0,160 (n = 8) 0,0180 0,0360 2

* mean of titrations of aliquots from eight separate bottles


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Figure 1: Mean result for each participant for Level 1 with their reported standard uncertainty (u). The assigned reference value for Level 1 (solid red line) is 0,3249 mg/g. The calculated combined standard uncertainty of the assigned reference value is 0,0011 mg/g. Dashed red lines show the assigned reference value ± uc (k = 1)

0.24

0.26

0.28

0.30

0.32

0.34

0.36

INM

KE

BS

VM

T/F

TM

C

NM

L-S

IRIM

INR

AP

VM

I

NM

ISA

INT

I

E.X

H.M NIS

DM

DM

Co

nce

ntr

atio

n (

mg

/g)

AFRIMETS.QM-K27Aqueous ethanol: Level 1

Comparison of results (standard uncertainty)


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Figure 2: Mean result for each participant for Level 1 with corresponding reported expanded uncertainty (U95%). The assigned reference value for Level 1 (solid red line) is 0,3249 mg/g. The expanded uncertainty for 95% coverage range of the assigned reference value (dashed red lines) is 0,0021 mg/g.

0.23

0.25

0.27

0.29

0.31

0.33

0.35

0.37

INM

KE

BS

VM

T/F

TM

C

NM

L-S

IRIM

INR

AP

VM

I

NM

ISA

INT

I

E.X

H.M NIS

DM

DM

Co

nce

ntr

atio

n (

mg

/g)


Comparison of results (expanded uncertainty)


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Figure 3: Mean result for each participant for Level 2 with their reported standard uncertainty (u). The assigned reference value for Level 2 (solid red line) is 4,6649 mg/g. The calculated combined standard uncertainty of the assigned reference value is 0,0076 mg/g. Dashed red lines show the assigned reference value ± uc (k = 1)

4.19

4.29

4.39

4.49

4.59

4.69

4.79

4.89

4.99

INR

AP

VM

T/F

TM

C

INM

INT

I

VM

I

NIS

NM

ISA

NM

L-S

IRIM

KE

BS

E.X

H.M

DM

DM

Co

nce

ntr

atio

n (

mg

/g)


Comparison of results (standard uncertainty)


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Figure 4: Mean result for each participant for Level 2 with corresponding reported expanded uncertainty (U95%). The assigned reference value for Level 2 (solid red line) is 4,6649 mg/g. The expanded uncertainty for 95% coverage range of the assigned reference value (dashed red lines) is 0,0152 mg/ .

4.19

4.29

4.39

4.49

4.59

4.69

4.79

4.89

4.99

INR

AP

VM

T/F

TM

C

INM

INT

I

VM

I

NIS

NM

ISA

NM

L-S

IRIM

KE

BS

E.X

H.M

DM

DM

Co

nce

ntr

atio

n (

mg

/g)


Comparison of results (expanded uncertainty)


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SOURCES OF UNCERTAINTY

The sources of uncertainty as identified by the participants are tabulated in Table 8. Table 8: Sources of uncertainty

Institute Uncertainty identified

INTI

- Repeatability intra aliquot - Reproducibility inter aliquot/bottle - SRM uncertainty - accuracy (bias)

2222 accuracytyuncertainSRMilityreproducibityrepeatabilu

NIS

1- Level 1 - Measurement precision 0.91% - Sample mass (Balance linearity) 0.006 % - Internal standard mass (Balance linearity) 0.003% - Calibration solution (Balance linearity and purity of ethanol) 0.005% - Combined standard uncertainty (%) 0.91 % - Combined standard uncertainty 0.003 mg g-1 - Coverage factor 2.0 - Combined expanded uncertainty 0.006 mg g-1

2- Level 2 - Measurement precision 0.35% - Sample mass (Balance linearity) 0.003% - Internal standard mass (Balance linearity) 0.003% - Calibration solution (Balance linearity and purity of ethanol) 0.005% - Combined standard uncertainty (%) 0.361% - Combined standard uncertainty 0.0163 mg g-1 - Coverage factor 2.0 - Combined expanded uncertainty 0.0327 mg g-1


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E.XH.M

value sample A sample B units

Method precision 1,00000 0,005900 0,079650 mg/g

EtOH conc. in calibrant 0,33441 0,000193 0,000193 mg/g

mass of calibrant 0,60000 0,000004 0,000004 g

mass of IS added to calibrant 0,60000 0,000004 0,000004 g

mass of sample 0,60000 0,000004 0,000004 g

mass of IS added to sample 0,60000 0,000004 0,000004 g

combined standard uncertainty 0,001982 0,026636 mg/g

coverage factor 2 2

expanded uncertainty 0,003965 0,053273 mg/g


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KEBS

Sample: Level 2

Description Value x Standard

Uncertainty µ(x)

Relative Standard Uncertainty µ(x)/x

(µ(x)/x)^2 Remark

Weighing Uncertainty 200.00 0.1200 0.0006 0.00000036

Calibration certificate of mass balance Q/16/Q23/55

Calibration error 0.0015 0.00034 0.221657879 0.049132215 Calibration error of estimate Sxo

Ethanol CRM Concentration

0.1951 0.0018 0.009226038 8.51198E-05

Calibration certificate

0.3900 0.0046 0.011794872 0.000139119

0.8023 0.0074 0.009223482 8.50726E-05

1.0084 0.0083 0.008230861 6.77471E-05

1.7010 0.0140 0.008230453 6.77404E-05

µ (Precision) 4.7526 0.0355 0.007471452 5.58226E-05 ESDM for Sample Level 2

µ (Bias) 0.9034 0.0196 0.021695816 0.000470708 ESDM for Recovery

0.050103905 0.002510401 Combined Relative Standard u (RSS)

0.011930949 Combined Standard u(x)c


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0.023861899 Expanded U (k=2)

0.502080259 % Relative U

Sample: Level 1

Description Value x Standard Uncertainty µ(x)

Relative Standard Uncertainty µ(x)/x

(µ(x)/x)^2 Remark

Weighing Uncertainty 500.00 0.1200 0.00024 5.76E-08

Calibration certificate of mass balance Q/16/Q23/55

Calibration error 0.0015 0.00034 0.221657879 0.049132215 Calibration error of estimate Sxo

Ethanol CRM Concentration

0.1951 0.0018 0.009226038 8.51198E-05

Calibration certificate

0.3900 0.0046 0.011794872 0.000139119

0.8023 0.0074 0.009223482 8.50726E-05

1.0084 0.0083 0.008230861 6.77471E-05

1.7010 0.0140 0.008230453 6.77404E-05

µ (Precision) 0.3009 0.0096 0.032008301 0.001024531 ESDM for Sample Level 1

µ (Bias) 0.9034 0.0196 0.021695816 0.000470708 ESDM for Recovery

0.051072311 0.002608381 Combined Relative Standard u (RSS)

0.000784919 Combined Standard u(x)c

0.001569838 Expanded U (k=2)

0.521676197 % Relative U

VMT/FCMT

1) Measurement of samples (A-type uncertainty) 2) Measurement of calibration standards (A-type uncertainty) 3) Concentration of calibration solution (B-type uncertainty) Measurement of samples uncertainty had relatively the biggest contribution in the overall uncertainty budget


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NML-SIRIM

Level 1

Level 2

Method precision21.818%

cz0.001%

method Bias78.145%

my0.012%

myc0.010%

mzc0.010%

mx0.004%

Method precision99.79%

cz0.0000002%

my0.05%

myc0.05%

mzc0.05%

mx0.05%


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INM

An example of the uncertainty budget for bottle 42, level 1, aliquot 2

Description Value Standard uncertainty

Relative standard uncertainty

V difference of volumes of titrant used

3.9 [ml] 0.0216 0.005538

ctitr molar concentration of titrant

0.1 [mol/L] 0.0015 0.00015

Ftitr factor of titrant 0.998 0.0005 0.0005

MC2H5OH molar mass of ethanol 46.06844 0.00118 0.0000256

fstoich stoichiometric factor 0.25 0 0

frep Repeatability 1 0.0146 0.0146

maliquot mass of aliquot 0.99925 [g] 0.00005 0.00005004

fb correction factor for buoyancy

0.99985 0.00005 0.00005001

wC2H5OH mass fraction of ethanol 4.48 0.06999 0.015624

DMDM

Relative contributions in % for all contributors

Rf B0 B1 Cint R

63.63 1.33 3.41 0.0060 31.62

B0 is the intercept of the calibration curve B1 is the slope of the calibration curve Cint is the mass concentration of the internal standard R is the recovery factor


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INRAP

Uncertainty due to variation in the extraction protocol or in the sample preparation is almost compensated by the use of internal standard calibration method. Nevertheless, the major components of the uncertainty are for level 1 (0,01g/100g) (For the other levels see the U(c) spreadsheet in the attached excel file).

Type A

uA(C)=0,00072g/100g

Type B :

uB (c) =0,00023 g/100g

uu BAcu 22)(

U(c)=K.u(c)

with k is coverage factor (k=2)

VMI

Level 1 Description Value x Standard uncertainty u(x)

Relative standard uncertainty u(x)/x

Repeatability 0.323 mg/g 0.00142 mg/g 0.0044

VVu

vvu

ccuCcu c

PEPEc

meremerec

B)()()(

)(222


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Concentration of titrant

0.050665 mol/l 0.0000182 mol/l 0.00036

Volume of titrant 26.18 ml 0.0245 ml 0.00094 Concentration of K2Cr2O7 solution

0.010478 g/g 0.000004 g/g 0.0003

Level 2 Description Value x Standard uncertainty u(x)

Relative standard uncertainty u(x)/x

Repeatability 4.664 mg/g 0.0114 mg/g 0.00244 Concentration of titrant

0.10047 mol/l 0.00003 mol/l 0.0003

Volume of titrant 19.15 ml 0.0245 ml 0.00128 Concentration of K2Cr2O7 solution

NMISA

[EtOH] = 100 * ([K2Cr2O7] / (4.2565 * MassEtOH soln)) * (MassK2Cr2O7 soln – (Titre(NH4)2Fe(SO4)2/ h)) mg/ 100g where [K2Cr2O7] is the concentration of the potassium dichromate solution used, in mg/g MassEtOH soln is the mass of the ethanol solution taken for analysis, in g MassK2Cr2O7 soln is the mass of the potassium dichromate solution aliquot added to the ethanol solution, in g Titre(NH4)2Fe(SO4)2 is the volume of ammonium iron sulphate titrant used for the aliquot, in ml the term ‘h’ refers to the blank, the average of the ratio of the ammonium iron sulphate titre to the mass of potassium dichromate titrated (titre(NH4)2Fe(SO4)2/ massK2Cr2O7). 1 gram ethanol reacts with 4.2565 grams K2Cr2O7


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Summary of uncertainty contributionsParameter x u(x) u(x)/x

u(Precision) 467.694 0.264871 0.000566u([K2Cr2O7]) 4.904341 0.002835 0.000578u(Conv) 4.257178 0.000112 2.63E-05

u(fox) 1 0.00113 0.00113

u(fimp) 1 0.0002 0.0002

u(Blank) 1.997706 0.002249 0.001126u(Titre) 10.36233 0.007054 0.000681

u(Prec is ion)

u([K2Cr2O7])

u(Conv)

u(fox )

u(f imp)

u(Blank)

u(T itre)

Comparison of uncertainty contributions


Page 27 of 40

DISCUSSION OF RESULTS

As discussed in past CCQM-K27 studies, the expected spread (%CV) of higher order

measurements of ethanol in aqueous medium is about 0,85% relative [3, 4]. In this study the

CV for Level 1 is about 12% (about 10% with two INM outliers removed) and for Level 2

about 4%.

In the CCQM-K27.2 study four of the five participating laboratories submitted results that

were within 1,5% of the gravimetric reference value. In the AFRMETS.QM-K27 study three

of the ten laboratories submitted (mean) results within 1,5% of the gravimetric reference

value for Level 1.

For Level 2 four of the ten participating laboratories submitted mean results within 1,5% of

the gravimetric reference value. The percentage difference from the assigned reference

value for both levels is presented in Figure 5. The NMISA titrimetric results are included for

reference.

Figure 5: Percentage differences from the assigned reference value for the AFRIMETS.QM-K27 study, where the solid red line represents the zero-bias line and the blue dotted lines the ± 1,5% difference from zero-bias levels. The results are plotted relative to the assigned reference value and the error bars represent the expanded uncertainties reported by each participating laboratory, converted to percentages. Level 1 is represented by pink markers and Level 2 by blue markers.

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-5

0

5

10

15

INM

- L

eve

l 1

INM

- L

eve

l 2

KE

BS

- L

eve

l 1

KE

BS

- L

eve

l 2

VM

T/F

TM

C -

Leve

l 1

VM

T/F

TM

C -

Leve

l 2

NM

L-S

IRIM

- L

eve

l 1

NM

L-S

IRIM

- L

eve

l 2

INR

AP

- L

eve

l 1

INR

AP

- L

eve

l 2

VM

I -

Leve

l 1

VM

I -

Leve

l 2

INT

I -

Le

vel 1

INT

I -

Le

vel 2

E.X

H.M

- L

eve

l 1

E.X

H.M

- L

eve

l 2

NIS

- L

eve

l 1

NIS

- L

eve

l 2

DM

DM

- L

eve

l 1

DM

DM

- L

eve

l 2

NM

ISA

- L

eve

l 1

NM

ISA

- L

eve

l 2

% D

iffe

ren

ce f

rom

assig

ne

d r

efe

ren

ce v

alu

e

AFRIMETS.QM-K27Percentage differences from assigned reference values for Level 1 and Level 2


Page 28 of 40

Two of the participating laboratories, Instituto Nacional de Tecnologia Industrial (INTI) and

Vietnam Metrology Institute (VMI), achieved mean results within 1,5% of the gravimetric

reference value for both levels.

The National Reference Laboratory in Chemical Metrology (E.XH.M-GCSL/EIM) from

Greece identified an error in their calculation formula after the draft report was released to all

participants. E.XH.M-GCSL/EIM re-submitted corrected results of 0,3284 mg/g for level 1

and 4,7460 mg/g for level 2. The corrected results have not been included with the reported

results, but have been recorded here for future reference if needed.

The results of the AFRIMETS.QM-K27 study are compared to those of the previous CCQM-

K27 studies in Figure 6. Although there was much interest and need for a comparison to

support this measurement capability, as reflected by the number of participants, it is clear

from Figure 6 that some NMIs still require improvement.

In Appendix 1, the degrees of equivalence of the results are summarized.

SUPPORTED CMC CLAIMS

The information in this report may be used by participants to support any future CMC claim

in the BIPM database relating to the assay of aqueous ethanol solutions for the respective

concentration ranges 0,1 mg/g to 5 mg/g determined in this study.

CONCLUSIONS

The majority of the results do not compellingly demonstrate the ability of the participants to

accurately measure ethanol in aqueous medium in the concentration range 0,1 mg/g to 5

mg/g. Participants in the AFRIMETS-K27 study would have benefited from a pilot study in

which to test their measurement capability prior to participation in the key comparison.

Several NMIs, however, will still be able to make new CMC claims based on their

performance in this comparison.


Page 29 of 40

Figure 6: Percentage differences of the results from the KCRV or assigned reference value for CCQM-K27a, CCQM-K27.1, CCQM-K27.2 and AFRIMETS.QM-K27. The results are plotted relative to the zero-bias line and the blue lines represent the ± 1% limits recommended in previous studies, except for Level 4 of the CCQM-K27.1 study which is 0,295%. The participants not previously mentioned in this report are: National Analytical Reference Laboratory, Australia (NARL), National Research Centre for Certified Reference Materials, China (NRCCRM), Laboratoire National d’Essais, France (LNE), Bundesanstalt fűr Materialforschung und –prűfung, Germany (BAM), National Metrology Institute of Japan (NMIJ), Korea Research Institute of Standards and Science (KRISS), D.I. Mendeleyev Institute for Metrology, Russia (VNIIM), Laboratory of the Government Chemist, United Kingdom (LGC), National Institute of Standards and Technology, USA (NIST), and the following countries: Brazil (INMETRO), Chile (CMQFC), Mexico (CENAM) and South Africa (CSIR-NML, now NMISA).

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-20

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-10

-5

0

5

10

15

BA

M-a

-AB

AM

-a-B

BA

M-a

-CK

RIS

S-a

-AK

RIS

S-a

-BLG

C-a

-ALG

C-a

-BLG

C-a

-CLN

E-a

-ALN

E-a

-BLN

E-a

-CN

AR

L-a

-AN

AR

L-a

-BN

AR

L-a

-CN

IST

-a-A

NIS

T-a

-BN

IST

-a-C

NM

IJ-a

-AN

MIJ

-a-B

NM

IJ-a

-CN

RC

CR

M-a

-AN

RC

CR

M-a

-BN

RC

CR

M-a

-CV

NIIM

-a-A

VN

IIM-a

-BV

NIIM

-a-C

CS

IR-N

ML-

S-1

CS

IR-N

ML-

S-2

CS

IR-N

ML-

S-3

CS

IR-N

ML-

S-4

LGC

-S-1

LGC

-S-4

VN

IIM-S

-1V

NIIM

-S-2

VN

IIM-S

-3V

NIIM

-S-4

INT

I-S

-1IN

TI-

S-2

INM

ET

RO

-S-1

INM

ET

RO

-S-2

CM

QF

C-S

-1C

MQ

FC

-S-2

CE

NA

M-S

-1C

EN

AM

-S-2

CS

IR-N

ML-

S-1

CS

IR-N

ML-

S-2

INT

I-S

-1IN

TI-

S-2

NIS

-S-1

NIS

-S-2

E.X

H.M

-S-1

E.X

H.M

-S-2

KE

BS

-S-1

KE

BS

-S-2

VM

T/F

TM

C-S

-1V

MT

/FT

MC

-S-2

NM

L-S

IRIM

-S-1

NM

L-S

IRIM

-S-2

INM

-S-1

INM

-S-2

DM

DM

-S-1

DM

DM

-S-2

INR

AP

-S-1

INR

AP

-S-2

VM

I-S

-1V

MI-

S-2P

erce

nta

ge

dif

fere

nce

fro

m K

CR

V/

assi

gn

ed r

efer

ence

val

ue

AFRIMETS.QM-K27CCQM-K27.2CCQM-K27.1CCQM-K27a


Page 30 of 40

REFERENCES

[1] http://kcdb.bipm.org/AppendixB/appbresults/ccqm-k27.a/ccqm-k27.a_final_report.pdf

[2] http://kcdb.bipm.org/AppendixB/appbresults/ccqm-k27.b/ccqm-k27.b_final_report.pdf

[3] http://kcdb.bipm.org/AppendixB/appbresults/ccqm-k27.1/ccqm-k27.1_final_report.pdf

[4] CCQM K27.2 Draft B report in progress

[5] CCQM K79 Draft B report in progress

[6] http://www.bipm.org/utils/common/CIPM_MRA/CIPM_MRA-D-05.pdf

[7] http://kcdb.bipm.org/appendixB/appbresults/ccqm-k27.1/ccqm-k27.1.pdf

COORDINATOR

Dr Maria Fernandes-Whaley National Metrology Institute of South Africa (NMISA) CSIR, Building 6 Meiring Naudé Road Brummeria, PRETORIA, South Africa, 0001 Tel: +27 12 841 2105 Fax: +27 86 509 5996 e-mail: [email protected] PROJECT REFERENCE

AFRIMETS.QM-K27 COMPLETION DATE

Estimated: October 2011


Page 31 of 40

APPENDIX 1 – DEGREES OF EQUIVALENCE

AFRIMETS has decided to present the information in this report in a format as close as

possible to that in the previous CCQM K27 key comparison studies for ethanol, where

participant results are compared by % difference to the KCRV or in this case to the assigned

reference value. For consistency the degrees of equivalence are presented as in the

summary results table for CCQM-K27.1.[7]Degrees of equivalence are often used to assess

laboratory bias. In general, results in which the uncertainty bars at least touch the zero-bias

line are considered acceptable.

The degrees of equivalence (Tables A1 and A2) with the assigned reference value were

calculated for each participant from Equation A1.

[Eqn. A1]

where xi is the mean participant result and X is the assigned reference value in mg/g

A graphical representation of the degrees of equivalence for Level 1 is given in Figure A1

and for Level 2 in Figure A2. The expanded uncertainties (Ui) are those reported by the

participating laboratories.

Table A3 presents the relative degrees of equivalence, Di rel, for CCQM-K27a, CCQM-K27.1,

CQM-K27.2 and AFRIMETS.QM-K27 together with the associated relative expanded

uncertainty, Ui rel. The graphical representation is presented in Figure A3. The relative terms

are defined in equations A2 and A3:

% [Eqn. A2]

% [Eqn. A3]


Page 32 of 40

Table A1: Degrees of equivalence for Level 1 and associated U95%(Di)

Institute Mean Standard

uncertainty, ui (mg/g)

Expanded uncertainty, Ui

(mg/g)

Di (mg/g)

INTI 0,3293 0,0026 0,0052 0,0044

NIS 0,3320 0,003 0,006 0,0071

E.XH.M 0,3303 0,0020 0,0040 0,0054

KEBS 0,3016 0,0008 0,0016 -0,0233

VMT/FTMC 0,306 0,003 0,006 -0,0189

NML-SIRIM 0,31 0,005 0,01 -0,0149

INM 0,245 0,0085 0,017 -0,0799

DMDM 0,3635 0,0028 0,0057 0,0386

INRAP 0,321 0,008 0,016 -0,0039

VMI 0,323 0,002 0,004 -0,0019

NMISA 0,3273 0,0012 0,0023 0,0024


Page 33 of 40

Table A2: Degrees of equivalence for Level 2 and associated U95%(Di)

Institute Mean Standard

uncertainty, ui (mg/g)

Expanded uncertainty, Ui

(mg/g)

Di (mg/g)

INTI 4,662 0,036 0,072 -0,0029

NIS 4,670 0,017 0,034 0,0051

E.XH.M 4,772 0,0266 0,0533 0,1071

KEBS 4,7526 0,0119 0,0239 0,0877

VMT/FTMC 4,49 0,04 0,08 -0,1749

NML-SIRIM 4,69 0,03 0,06 0,0251

INM 4,59 0,07 0,14 -0,0749

DMDM 5,00991 0,022 0,045 0,3450

INRAP 4,22 0,013 0,026 -0,4449

VMI 4,664 0,021 0,045 -0,0009

NMISA 4,6749 0,0180 0,0360 0,0100


Page 34 of 40

Figure A1: Degrees of equivalence for Level 1. The expanded uncertainties are those reported

by the participating laboratories.

Figure A2: Degrees of equivalence for Level 2. The expanded uncertainties are those reported by the participating laboratories.

-0.10

-0.05

0.00

0.05

INM

KE

BS

VM

T/F

TM

C

NM

L-S

IRIM

INR

AP

VM

I

NM

ISA

INT

I

E.X

H.M NIS

DM

DM

Di (

mg

/ g)


-0.50

-0.30

-0.10

0.10

0.30

0.50

INR

AP

VM

T/F

TM

C

INM

INT

I

VM

I

NIS

NM

ISA

NM

L-S

IRIM

KE

BS

E.X

H.M

DM

DM

Di(m

g/ g

)



Page 35 of 40

Table A3: Relative degrees of equivalence, Di rel, for the CCQM-K27 series of ethanol comparisons and AFRIMETS.QM-K27 and the associated relative expanded uncertainty, Ui rel.

Di rel Ui rel Di rel Ui rel Di rel Ui rel

/ % / % / % / % / % / %BAM K27.a A -0.14 0.61 CSIR-NML K27.1 1 0.72 2.05 INTI 1 1.35 1.60

K27.a B -0.02 0.64 K27.1 2 0.52 1.1 2 -0.06 1.54K27.b C -0.15 0.63 K27.1 3 0.37 1.11 NIS 1 2.19 1.85

KRISS K27.a A -0.34 1.25 K27.1 4 0.17 1.16 2 0.11 0.73K27.a B -0.29 1.14 LGC K27.1 1 -0.11 0.22 E.XH.M 1 1.66 1.23K27.b C - - K27.1 2 - - 2 2.30 1.14

LGC K27.a A -0.07 0.1 K27.1 3 - - KEBS 1 -7.17 0.49K27.a B -0.07 0.17 K27.1 4 -0.57 0.44 2 1.88 0.51K27.b C 0.15 0.18 VNIIM K27.1 1 0.21 0.62 VMT/FTMC 1 -5.82 1.85

LNE K27.a A 2.33 1.7 K27.1 2 0.3 0.59 2 -3.75 1.71K27.a B 0.63 1.66 K27.1 3 -0.13 0.67 NML-SIRIM 1 -4.59 3.08K27.b C -0.2 1.85 K27.1 4 -0.38 0.8 2 0.54 1.29

NARL K27.a A 0.06 0.42 CENAM K27.2 1 -1.28 1.64 INM 1 -24.59 5.23K27.a B -0.02 0.52 K27.2 2 -1.26 2.20 2 -1.61 3.00K27.b C 0.12 0.81 CSIR-NML K27.2 1 -0.73 0.55 DMDM 1 11.88 1.75

NIST K27.a A 1.74 1.06 K27.2 2 0.31 0.31 2 7.40 0.96K27.a B -0.17 0.99 K27.2 1 1.46 1.09 INRAP 1 -1.20 4.92K27.b C 0.06 0.97 K27.2 2 1.26 0.94 2 -9.54 0.56

NMIJ K27.a A -0.14 0.37 INMETRO K27.2 1 -0.36 0.36 VMI 1 -0.58 1.23K27.a B -0.3 0.61 K27.2 2 0.00 0.31 2 -0.02 0.96K27.b C 0.46 0.38 INTI K27.2 1 -13.69 0.91 1 0.74 0.71

NRCCRM K27.a A 0.1 0.45 K27.2 2 -14.15 0.94 2 0.21 0.77K27.a B -0.14 0.5K27.b C -0.33 0.47 Where Di rel % = Di x 100/ X ref value

VNIIM K27.a A -2.99 1.03 and Ui rel % = Ui x 100/ X ref valueK27.a B -0.83 0.83 Data obtained from CCQM K27.1 summary table [7]K27.b C -1.02 1.49 Data calculated from CCQM K27.2 Draft A report [4]

FUND.CHILE

NMISA (CSIR-NML)

AF

RIM

ET

S.Q

M-K

27

Lab iKey

ComparisonSampleLab i

Key Comparison

Sample Lab iKey

ComparisonSample


Page 36 of 40

Figure A3: Percentage degrees of equivalence of the results from the KCRV or assigned reference value for CCQM-K27, CCQM-K27.1, CCQM-K27.2 and AFRIMETS.QM-K27. The results are plotted relative to the zero-bias line and the blue lines represent the ± 1% limits recommended in previous studies, except for Level 4 of the CCQM-K27.1 study which is 0,295%.

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-25

-20

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-10

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0

5

10

15B

AM

-a-A

BA

M-a

-BB

AM

-a-C

KR

ISS

-a-A

KR

ISS

-a-B

LGC

-a-A

LGC

-a-B

LGC

-a-C

LNE

-a-A

LNE

-a-B

LNE

-a-C

NA

RL

-a-A

NA

RL

-a-B

NA

RL

-a-C

NIS

T-a

-AN

IST

-a-B

NIS

T-a

-CN

MIJ

-a-A

NM

IJ-a

-BN

MIJ

-a-C

NR

CC

RM

-a-A

NR

CC

RM

-a-B

NR

CC

RM

-a-C

VN

IIM-a

-AV

NIIM

-a-B

VN

IIM-a

-C

CS

IR-N

ML-

S-1

CS

IR-N

ML-

S-2

CS

IR-N

ML-

S-3

CS

IR-N

ML-

S-4

LGC

-S-1

LGC

-S-4

VN

IIM-S

-1V

NIIM

-S-2

VN

IIM-S

-3V

NIIM

-S-4

INT

I-S

-1IN

TI-

S-2

INM

ET

RO

-S-1

INM

ET

RO

-S-2

CM

QF

C-S

-1C

MQ

FC

-S-2

CE

NA

M-S

-1C

EN

AM

-S-2

CS

IR-N

ML-

S-1

CS

IR-N

ML-

S-2

INT

I-S

-1IN

TI-

S-2

NIS

-S-1

NIS

-S-2

E.X

H.M

-S-1

E.X

H.M

-S-2

KE

BS

-S-1

KE

BS

-S-2

VM

T/F

TM

C-S

-1V

MT

/FT

MC

-S-2

NM

L-S

IRIM

-S-1

NM

L-S

IRIM

-S-2

INM

-S-1

INM

-S-2

DM

DM

-S-1

DM

DM

-S-2

INR

AP

-S-1

INR

AP

-S-2

VM

I-S

-1V

MI-

S-2

NM

ISA

-S-1

NM

ISA

-S-2

Dire

l/ %

AFRIMETS.QM-K27CCQM-K27.2CCQM-K27.1CCQM-K27a

Black: Sample A ~ 0.8 mg/gGreen: Sample B ~ 120 mg/g

Black: Level 1~ 0.2 mg/gOrange: Level 2~ 1 mg/gPurple: Level 3~ 3 mg/gBlue: Level 4 ~ 60 mg/g

Orange: Level 1~ 0.5 mg/gBlue: Level 2 ~ 3 mg/g

Pink: Level 1~ 0.3 mg/gBlue: Level 2 ~ 5 mg/g


Page 37 of 40

APPENDIX 2 - STANDARD DEVIATION FOR PROFICIENCY ASSESSMENT

The AFRIMETS.QM-K27 study was conducted for metrology institutes and linked to the

CCQM-K27 series of studies with the intention of assisting these institutes in submitting

CMC claims. As such, above-average accuracy and precision are expected. The following

approaches are used in proficiency testing schemes for routine laboratories. These

approaches serve to illustrate that some of the results are acceptable at routine laboratory

level, but would require further investigation and improvement to be accepted at CCQM

level. No CMC claims can be made on these approaches.

The ISO document, ISO 13528:2005: Statistical methods for use in proficiency testing by

interlaboratory comparisons, gives several options for estimating the standard deviation for

proficiency assessment, viz:

1. Prescribed method, e.g., legislation

2. By perception, i.e., the level of competence that it is desirable to achieve

3. From a general model, e.g., the Horwitz curve

4. From the results of a precision experiment: a standard method is used

5. From data obtained in a round of a proficiency testing scheme, i.e., from participant

results.

This standard deviation is then used to determine whether the results are acceptable or not.

Option 1 and 4 above are clearly not applicable to AFRIMETS.QM-K27.

Option 2 is applied in the main report. That is, from previous studies a spread (CV) of 0,85%

relative and accuracy of not more than ± 1% is desirable for the range of concentrations,

bearing in mind that the results are generated by metrology institutes. Also refer to Figures

A4 and A5.

The Horwitz model in Option 3 may be applicable for routine laboratories where no data

exists to provide a starting point. It is certainly not applicable to the results of expert

laboratories such as metrology institutes. The Horwitz 2s (U) limits for Level 1 are ± 13,4%

relative (dotted red lines in Figure A6) and ± 9% relative for Level 2 (dotted red lines in

Figure A7).

For Option 5, two approaches are possible; from the results of a single study or from the

results of a long-term study. In Figures A6 and A7, the expanded uncertainty for a long-term


Page 38 of 40

study coordinated by NMISA is given (aqueous ethanol by headspace gas chromatography-

FID).

i) By perception, i.e., the level of competence that it is desirable to achieve

In CCQM-K27a, the expected uncertainty was calculated from Equation A4, using the

participant data [1].

.

√ [Eqn A4]

Where U is the expanded uncertainty, the t value was used as the coverage factor, s is

the standard deviation and n is the number of participants.

For AFRIMETS.QM-K27 this yields ± 6,7% relative U (2s) for Level 1 (dotted red lines in Figure A4) and ± 3,1% relative U (2s) for Level 2 (dotted red lines in Figure A5), when all the results are included.

Figure A4: Comparison of CCQM-K27a and participant uncertainties, Level 1. Dotted blue lines: ±1% relative expanded uncertainty (CCQM-K27a). Dotted red lines: 2s limits calculated from participant results (± 6,7% relative). The solid red line is the assigned reference value (0,3249 mg/g).

0.22

0.26

0.30

0.34

0.38

INM

KE

BS

VM

T/F

TM

C

NM

L-S

IRIM

INR

AP

VM

I

NM

ISA

INT

I

E.X

H.M NIS

DM

DM

Co

nce

ntr

atio

n (

mg

/g)

Assigned reference value: 0,3249 ± 0,0021 mg/g



Page 39 of 40

Figure A5: Comparison of CCQM-K27a and participant uncertainties, Level 2. Dotted blue lines: ±1% relative expanded uncertainty (CCQM-K27a). Dotted red lines: 2s limits calculated from participant results (± 3,1% relative). The solid red line is the assigned reference value (4,6649 mg/g).

ii) From a general model (Horwitz curve) and from data obtained in a proficiency testing

scheme (participant results)

The NMISA has coordinated a proficiency testing scheme for routine laboratories for a

number of years. All the participants use headspace gas-chromatography with flame

ionisation detection (HS-GC-FID). From this data, a model can be generated which gives

the recommended 2s (U) limit for Level 1 as ±10,6% relative (dotted blue lines in Figure

A6) and for Level 2 ±5,5% relative (dotted blue lines in Figure A7). Since the

AFRIMETS.QM-K27 study includes results obtained by other techniques, this model may

not be applicable to the results. However, when the same model is applied to the results

of CCQM-K27a, CCQM-K27.1 and CCQM-K27.2 (where different analytical techniques

were used), the mean 2s limits are ± 2,2% relative for the concentration range 0,1 to 5

mg/g. This indicates that the techniques used did not influence the precision of the

results.

4.15

4.35

4.55

4.75

4.95IN

RA

P

VM

T/F

TM

C

INM

INT

I

VM

I

NIS

NM

ISA

NM

L-S

IRIM

KE

BS

E.X

H.M

DM

DM

Co

nce

ntr

atio

n (

mg

/g)




Page 40 of 40

Figure A6: Comparison of Horwitz and NMISA study uncertainties, Level 1. Blue dotted lines: ± 10,6% expanded uncertainty, U (from NMISA HS-GC-FID study), red dotted lines: ± 13,4% relative U (Horwitz). The solid red line is the assigned reference value (0,3249 mg/g).

Figure A7: Comparison of Horwitz and NMISA study uncertainties, Level 2. Blue dotted lines: ± 5,5% expanded uncertainty, U (from NMISA HS-GC-FID study), red dotted lines: ± 9% relative U (Horwitz). The solid red line is the assigned reference value (4,6649 mg/g).

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