Ural Scientific Research Institute for Metrology,
ROSSTANDART, RUSSIA








Report of the CCQM-K130

Nitrogen mass fraction measurements in glycine

FINAL REPORT: July 2016

Coordinating laboratory:
Ural Scientific Research Institute for Metrology, ROSSTANDART,
Ekaterinburg, UNIIM
Maria Medvedevskikh, Bessonov Jury, Maria Krasheninina



With contributions from:
INACAL, Perú: Steve Ali Acco Garcia
SP, Sweden: Conny Haraldsson
INTI-1, Argentina: M. Alejandra Rodriguez, Gabriela Rodriguez
LATU, Uruguay: Karino Salvo
UkrCSM, Ukraine: Vladimir Gavrilkin, Sergey Kulik
MSL, New Zealand: Laly Samuel
Inmetro, Brazil: Eliane C. P. do Rego, Wagner Wollinger, Tânia M. Monteiro,
Lucas J. de Carvalho





Ekaterinburg
2016

Table of content

1 ABSTRACT ................................................................................................................................ 3
2 INTRODUTION ........................................................................................................................ 4
3 LIST OF PARTICIPANTS ........................................................................................................ 5
4 SAMPLE .................................................................................................................................... 6
5 INSTRUCTIONS FOR PARTICIPANTS ............................................................................... 10
6 METHODS OF MEASUREMENT ......................................................................................... 10
7 RESULTS AND DISCUSSION ............................................................................................... 12
7.1 Uncertainty ......................................................................................................................... 12
7.2 Formulas ............................................................................................................................. 14
7.3 Nitrogen mass fraction in glycine ....................................................................................... 15
7.4 Discussion ........................................................................................................................... 19
8 EQUIVALENCE STATEMENTS ........................................................................................... 19
9 CONCLUSIONS ...................................................................................................................... 19
10 ACKNOWLEDGEMENTS .................................................................................................... 19
11 REFERENCES ....................................................................................................................... 19
Appendix A – Technical Protocol ................................................................................................ 20

1 ABSTRACT

Mass fraction of nitrogen is very important pointer because the results of these
measurements are often used for determination of protein mass fraction that is an important
indicator of the quality of the vast majority of food products and raw materials, in particular dry
milk powder. Proteins-enzymes catalyze chemical reactions, protein along with fats and
carbohydrates is one of the indicators characterizing the energy value of food, so its definition is
mandatory for all food products.
The aim of this key comparison CCQM-K130 and pilot study P166 is to support National
Measurement Institutes (NMIs) and Designated Institutes (DIs) to demonstrate the validity of the
procedures the employed for determination of nitrogen mass fraction in glycine.
The study material for this key comparison and pilot study has been selected to be
representative as one of the aminoacid – the simplest part of the protein. Glycine is an amino acid,
single acid that does not have any isomers (melting point –290 °C; specific heat of
evaporation − 528,6 J/kg; specific melting heat − 981,1 J/kg; pKa − 2,34, molar
mass - 75,07 g/mol, density - 1,607 g/cm3).
Ural Scientific Research Institute for Metrology (UNIIM) acted as the coordinating
laboratory of this comparison and pilot study.
Eight NMIs participated in this key comparison and two NMIs participated in Pilot study.
The results of Pilot study are excluded from the Report B.

2 INTRODUTION


Nitrogen mass fraction is a relevant indicator for food products and food raw materials.
Kjeldahl Titrimetric method is often used for the measurements of this pointer. Despite the
occurrence of a number of the other methods for the measurements of nitrogen content, such as
Dumas method, infrared spectroscopy, chromatography etc., Kjeldahl method remains the most
accurate and reliable method of the measurement of nitrogen (protein) mass fraction. Kjeldahl
method is admitted as a reference method by various organizations, the most known of them are
listed [1]:
− AOAC International
− American Oil Chemists’ Society
− American Public Health Association (APHA)
− American Society for Testing and Materials (ASTM)
− Association of American Cereal Chemists
− European Commission
− International Dairy Federation (IDF)
− International Organization for Standardization (ISO)
− U.S. Department of Agriculture
U. S. Environmental Protection Agency (EPA)
But according to technical report participants are allowed to use any suitable methods of
analysis.
There are no CMCs in measurement of nitrogen mass fraction in glycine in the database
of BIPM. But China NIM (National Institute of Metrology) has calibration and measurement
capabilities in determination of nitrogen mass fraction in non fat milk powder. Mechanism for
measurement service delivery of this CMC is kept by CRM GBW08509. This CMC was approved
on 13 June 2013.
But key comparison has never been carried out in the field of measurement both glycine
and milk powder.

3 LIST OF PARTICIPANTS


Eight NMIs or DIs participated in the key comparison CCQM-K130. Table 1 contains the
full names of all participating NMIs and DIs and contact persons.

Table 1 List of participants
Institute Abbreviation Country Contact persons
Kind of
comparison
National Institute of
Metrology, Quality and
Technology
INMETRO Brazil
Eliane C. P. do Rego,
Wagner Wollinger,
Tânia M. Monteiro,
Lucas J. de Carvalho
Key
Instituto Nacional de
Calidad
INACAL Perú
Steve Ali Acco
Garcia
Key
SP Technical Research
Institute of Sweden
SP Sweden
Conny Haraldsson

Key
National Institute of
Industrial Technology INTI-1 Argentina
M. Alejandra
Rodriguez, Gabriela
Rodriguez
Key
Laboratorio Tecnológico
del Uruguay
LATU Uruguay Karino Salvo Key
State Enterprise All-
Ukrainian State Research
and production Center of
Standardization
Metrology, Certification
and Consumers’ Rights
Protection
UkrCSM Ukraine
Vladimir Gavrilkin,
Sergij Kulyk
Key
Measurement Standards
Laboratory of New
Zealand
MSL
New
Zealand
Laly Samuel Key
Ural Scientific Research
Institute for Metrology
UNIIM Russia
Maria
Medvedevskikh,
Maria Krasheninina

Key

4 SAMPLE

The comparison material for the CCQM-K130 was analytical grade glycine from a
commercial supplier. The material was supplied as a white solid and was not subject to further
purification. The analysis certificate provided with the material describes its purity as 99,7 %. This
material of glycine was subdivided into vials from dark glass. But before packing material of glycine
was dried until dry substances under the temperature of 105 degrees above zero during two hours.
Then vials were packaged in double waterproof bags. Each vial contains 5 g.
After preparation of the samples, homogeneity test has been carried out. Homogeneity test
for glycine is presented in table 2.

Table 2 Results of homogeneity testing between bottles (5 replicates for each bottle)

Vial
Nitrogen mass fraction, % Mean
value in
vial, % 1 2 3 4 5
1 18,57 18,48 18,56 18,53 18,47 18,52
2 18,57 18,53 18,51 18,56 18,45 18,52
3 18,47 18,42 18,50 18,44 18,53 18,47
4 18,52 18,50 18,51 18,47 18,62 18,52
5 18,72 18,50 18,52 18,55 18,66 18,59
6 18,66 18,50 18,67 18,54 18,46 18,57

In order to estimate the inhomogeneity contribution
hu
, a 1-way Analysis of Variances
(ANOVA) has been carried out with the experimental homogeneity data (table 1). The standard
uncertainty due to (in)homogeneity,
hu
, value for glycine (see Table 3, 4) were calculated according
to ISO Guide 35 using the Equations (1) and (2).

among within
h
MS MS
u
n


(1)
4
2
(n 1)
within
h
MS
u
n N


, (2)
where N=6, n=5.

Table 3 ANOVA analysis
Vial number sum average dispersion
1 5 92,619 18,524 0,0022
2 5 92,611 18,522 0,0024
3 5 92,363 18,473 0,0022
4 5 92,619 18,524 0,0031
5 5 92,944 18,589 0,0089
6 5 92,833 18,567 0,0093

Table 4 ANOVA analysis
source SS df MS F
Among 0,040918 5 0,008184 1,7524
Within 0,112078 24 0,004670
Sum 0,15299 29
standard uncertainties due to
inhomogeneity, uh 0,027 % Equation (1)
standard uncertainties due to
inhomogeneity, uh - - Equation (2)
relative standard uncertainties due
to inhomogeneity, uho 0,14 %

Stability test for glycine is presented in table 5 and figure 1. Long-term stability study has
been conducted with the help of isochronous experiment. Four samples were being kept in the
drying oven under the temperature (90±5) С. Time of sample keeping in such conditions is
accounted according to equation:
1 0
10
2
t t
T



, (3)
где  –time of conducting the experiment, days;
T – estimated shelf life, days;
1t - temperature of testing of samples (90±5), °C;
0t - temperature of keeping of samples, °C.


Table 5 Results of measurement of nitrogen mass fraction in glycine
№ Date Nitrogen mass fraction, %
1 21.08.2015 18,52
2 24.09.2015 18,56
3 26.11.2015 18,46
4 21.12.2015 18,70
mean of stability test, Xs 18,56
standard deviation of the data of key comparison
participants, S 0,10
Xs+S 18,66
Xs-S 18,46
slope,b 0,0073
standard uncertainty of slope,
slopeu
0,0071
confidence interval
0,05;( 2)n slopet u 
0,03
standard uncertainty due to long-term (in)stability,
su
0,67
relative standard uncertainty due to long-term
(in)stability,
sou
, % 0,32
time measurements in key comparison, t, days
(according to isochronous experiment) 360

Figure.1 - Stability test for glycine
Data in table 5 was accounted using linear regression method. Standard uncertainty
due to instability was calculated using formula:
s slopeu u t 
, (4)
Additionally, standard uncertainty due to short-term instability has been estimated. The
statistical evaluation of the homogeneity, long-term and short-term stability has indicated that
standard uncertainties due to inhomogeneity is 0,027 %, and long-term instability is 0,042 % and
short-term instability is 0,012 %.
The samples has been sent to the participants by DHL on 19th August 2015. Each sample
has been accompanied by veterinary certificate of international view. All samples arrived to their
destination without damage but for different countries, it has taken different time: from several
days to two month. The dispatch dates and receipt dates are given in Table 6.
The deadline for reporting results was set by end of February 2016 in order to prepare a
presentation for discussion at the CCQM IAWG meeting in April 2016. All participants reported
their results in time (except LATU and INTI).



W = 0,007333t + 18,450000
18,20
18,30
18,40
18,50
18,60
18,70
18,80
18,90
0 1 2 3 4 5
N
it
ro
g
en
m
as
s frac
ti
o
n
,
%
Time, mounth
Mean of stability test results - 1S
Mean of stability test results - 1S

Table 6 Sample sent dates, receipt dates and report dates
Institute Sample dispatch date Sample receipt date Date report sent
INMETRO 19 August 2015 28 August 2015 29.02.2016
INACAL 19 August 2015 23 November 2015 29.02.2016
SP 19 August 2015 2 September 2015 29.02.2016
INTI-1 19 August 2015 16 September 2015 29.02.2016
LATU 19 August 2015 26 August 2015 10.03.2016
UkrCSM 19 August 2015 2 September 2015 29.02.2016
MSL 19 August 2015 2 September 2015 29.02.2016

5 INSTRUCTIONS FOR PARTICIPANTS

Technical protocol has been sent to the participants by e-mail.
The technical protocol (appendix A) contained background information, timing of the
comparison, and information on the participating institutes. Information on sample preparation
and recommendation of condition for measurements was given.
Each participant is allowed to use any suitable method of analysis.
Participants were requested the results of nitrogen mass fraction in glycine. The results
should be reported accompanied by a full uncertainty statement (including a combined standard
uncertainty and an expanded uncertainty with a coverage factor applied). In addition, the report
should include technical details on the measurement procedure, traceability links (as calibrations)
and uncertainty contributions.

6 METHODS OF MEASUREMENT

Seven participants used Kjeldahl method for the measurements and one participant used
elemental method of analysis. Some details on measurements as derived from the reports are given
in Table 7 and Table 8.
Table 7 Details of sample mass and titrant
Institute Method of analysis Approx. sample mass, g
Titrant, its molar
concentration
INMETRO
Kjeldahl 0,7
Sulphuric acid
0,25 M
INACAL
Kjeldahl 0,500±0,005
Hydrochloric acid,
0,1 M
SP
Elemental method 0,035 -
INTI-1
Kjeldahl 0,130±0,007
Hydrochloric acid,
0,1 M
LATU
Kjeldahl 0,155±0,005
Hydrochloric acid,
0,1 M
UkrCSM
Kjeldahl 0,15±0,1
Sulphuric acid
0,05 M
MSL
Kjeldahl 0,15
Hydrochloric acid,
0,1 M
UNIIM
Kjeldahl 0,16±0,1
Sulphuric acid
0,05 M

Table 8 Traceability details
Institute Traceability
INMETRO
Traceability is provided by using calibration material: buffer materials
(pH=4,01±0,02 (25 ºC); pH=7,00±0,02 (25 ºC)). These buffer materials were
acquired for automatic titrator Metrohn and were verified by Electrochemical
Laboratory from Inmetro, whose is a CRM producer for pH solutions, using the
pH primary measuring system.
INACAL Traceability is provided by using potassium hydrogen phthalate (KHP) that is
certified by coulometric titration.
SP Traceability is provided by using calibration material: TRIS reference from
Slovak Institute of Metrology LOT A0704414.
INTI-1
Traceability is provided by using:
- Hydrochloric acid, 0,1 M (f=1) TitriPUR, Batch HC393273. The
concentration of this volumetric solution was determined with volumetric
standard TRIS (Merck).The determined titer at 20°C was 1,000 with an
expanded measurement uncertainty of ±0,003 (k=2 coverage factor for
95% coverage probability). The certified value is traceable to primary standard
NIST SRM 723e by means of volumetric standard TRIS, measured
in the accreditated calibration laboratory of Merck KGaA in accordance to DIN
EN ISO/IEC 17025.
- L-Tryptophan, Merck, assay (perchloric acid titration, calculated on dry
substance) > 99,0%.
- Ammonium sulfate, Merck, assay (alkalimetric) > 99,5%.
- Glycine, Merck, minimum assay (perchloric acid titration) 99,7% (mass
fraction).
LATU
Traceability is provided by using:
- Tris (hydroxymethil) aminomethane, reference material for acidimetry,
traceable to NIST Standard Reference Material (SRM), lot 122408J, shelf life
2017/03/31.
- L-Tryptophan certified reference material TraceCERT, EXP Jun/16 FLUKA
lot BCBH4262V.
UkrCSM
Traceability is provided by using:
Certified reference material of Sodium carbonate NIOCHIM
(DSZU 023.36-06); mass fraction of Sodium carbonate 99.668 % in dried at
270 – 300 °C material that is certified by titration.
MSL
Traceability is provided by using:
-NMIJ CRM3201-a05- 0.1mol/kg HCl traceable to SI and certified by
coulometric titration.
UNIIM
Traceability is provided by using:
- UNIIM GSO 10450-2014 (high purity sodium carbonate that is used for
determination molar concentration of sulphuric acid) that is certified by
coulometric titration.

7 RESULTS AND DISCUSSION
7.1 Uncertainty
Participants have used different approaches for estimations of measurement uncertainty of
nitrogen mass fraction by Kjeldahl method and Elemental method of analysis and have accounted
different sources of uncertainty in budget of uncertainty. Some details about sources of uncertainty
are given in Table 9.
Table 9 Details about results and sources of uncertainty
Institute Accounted sources of uncertainty
INMETRO
Type A
- repeatability of measurement results
Type B
- standard uncertainty due to volume of titrant in blank
- standard uncertainty due to volume of titrant in sample
- standard uncertainty due to factor of titrant
- standard uncertainty due to sample mass
INACAL
Type A
- repeatability of measurement results
Type B
- standard uncertainty due to molecular weight of nitrogen and potassium
hydrogen phthalate
SP
Type A
- mean instrument signal for test portion 1
- mean instrument signal for Reference for test portion 1
- mean instrument signal for test portion 2
- mean instrument signal for Reference for test portion 2
- mean instrument signal for test portion 3
- mean instrument signal for Reference for test portion 3
Type B
- amount content of base expressed as TRIS
- atomic weight of nitrogen
INTI-1
Type A
- repeatability of measurement results.
Type B
- standard uncertainty due to sample weight
- standard uncertainty due to titrant volume of hydrochloric acid standard
volumetric solution (blank and test sample)
- standard uncertainty due to concentration of hydrochloric acid standard
volumetric solution
INTI-2
Type A
- standard uncertainty type A was not presented.
Type B
-standard uncertainty due to titrant volume of hydrochloric acid standard
volumetric solution (blank and test sample)
-standard uncertainty due to sample weight
-standard uncertainty due to concentration of hydrochloric acid standard
volumetric solution
-standard uncertainty due to repeatability
LATU
Type A
- repeatability of measurement results
Type B
- standard uncertainty due to titration of hydrochloric acid standard volumetric
solution (blank and test sample)

- standard uncertainty due to sample mass
- standard uncertainty due to concentration of the hydrochloric acid
- standard uncertainty due to reproducibility of the laboratory on different days
UkrCSM
Type A
- repeatability of measurement results
Type B
- sample weighting
- EP determination
- titrant volume determination
- titrant concentration determination
- nitrogen atomic mass uncertainty
MSL
Type A
- repeatability of measurement results.
Type B
- standard uncertainty due to volumetric including pipette, burette and
volumetric flask-calibration, repeatability, readability and end point bias
- standard uncertainty due to standardization of NaOH
- standard uncertainty due to CRM
- standard uncertainty due to moisture measurement
- standard uncertainty due to balance calibration, repeatability, buoyancy
- standard uncertainty due to sample weight
- standard uncertainty due to method recovery
- standard uncertainty due to homogeneity
UNIIM
Type A
- repeatability of measurement results
Type B
- standard uncertainty due to sample weight
- standard uncertainty due to titrant volume of sulphuric acid standard
volumetric solution (blank and test sample)
- standard uncertainty due to concentration of sulphuric acid standard
volumetric solution
- standard uncertainty due to certified value of GSO 10450-2014 that was used
for determination of molar concentration of sulphuric acid
- standard uncertainty due to detection of end point of titration

7.2 Formulas
Preliminary inspection of value
ix
and associated uncertainties
 iu x
has been carried out
in accordance with CCQM guidance note [2] using the following equation


( )
( )
i
i
x med x
u x

, (5)
The results of preliminary inspection have shown that in general there are consistent results
with a small number of outlying results. It means that it’s case – C according to the CCQM
guidance.

Check of consistency have performed according to the CCQM guidance note [3] using
algorithm is shown bellow (only results of participants key comparison used for calculation).
 
 
2
21
1
/
1/
m
i i
u m
i
i
i
x u x
x
u x



, (6)

 
2
2
1
m
i u
obs
i i
x x
u x


 
   
 

, (7)
where
ix
- result of value of i NMI,
 u x
- standard uncertainty of
x
.
After calculations using formulas (6), (7) was compared
2
obs
with m-1 and with
2
0.05,m 1 
,
the 95 percentile of
2
with m-1 of freedom.
If
2 1obs m  
, it is normally safe to proceed with the assumption that the results are
mutually consistent and that the uncertainties account fully for the observed dispersion of values.
If
2 2
0.05,m 11 obsm     
the data provide no strong evidence that the reported uncertainties
are inappropriate, but the remains a risk that additional factors are contributing to the dispersion.
Refer to the prior working group decision on presumptive consistency and proceed accordingly.
If
2 2
0.05,m 1obs  
the data should be considered mutually inconsistent.

Candidates of the key comparison reference values (KCRV) were estimated following the
CCQM guidance note [2] using different approaches. The result from participant in the parallel
pilot study has not been taken into account to determine the KCRV. Results and uncertainties have
been taken from the reports as they were. Formulas for calculation are shown bellow.


1
1 m
i
i
x x
m 
 
, (8)
 
 
 
2
1
1
m
i
i
x x
u x
m m





, (9)
where
ix
- result of value of i NMI,
 u x
- standard uncertainty of
x
.







Uncertainty-weighted mean

1
m
u i i
i
x w x


, (10)
 
 
2
2
1
1/
1/
i
i m
i
i
u x
w
u x



, (11)

 
 22
1
1
1/
m
i
iu
u x
u x 

, (12)
where
 iu x
- standard uncertainty of
ix
.


Median

 
 
 
/2 /2 1
1 /2
1
,
2
,
m m
m
x x even m even
med x
x m odd


 
  
  
 
 
, (13)

  2 2
2
u med x
m
 
, (14)

 1.483 imed d 
, (15)
where
 i id x med x 
.

7.3 Nitrogen mass fraction in glycine
The reported values of nitrogen mass fraction and uncertainties of all results have been
summarized in Table 10. Estimations of candidates KCRV have been obtained by different
approaches (arithmetic mean, weighted mean, median) are presented in Table 10 (only results of
participants key comparison used for calculation KCRV). The same results are displayed
graphically in Figures 2, 3.
It is proposed to use the median of the KCRV, because:

2 2
0.05,m 1obs  
in this case the data is mutually inconsistent,
The reported uncertainties are not very different,
There two extreme values according to
    /i ix med x u x
,
According to figure 2 transformed distribution for reported results of NMIs and DIs for
nitrogen mass fraction is asymmetric.











Table 10 – Reported values of nitrogen mass fraction and uncertainties

№
Kind
of
com-
pari-
son
NMI/
DIS
Nitrogen
mass
fraction,
%
Combined
standard
uncertainty,
uc, %
Expanded
uncertainty,
U(k=2), %
di, % U(di), % Verdict
1 2 3 4 5 6 7 8 9
1 Key INACAL 18,508 0,04 0,07 -0,05 0,09 +
2 Key LATU 18,513 0,07 0,13 -0,05 0,14 +
3 Key MSL 18,524 0,09 0,17 -0,04 0,18 +
4 Key UNIIM 18,535 0,05 0,11 -0,03 0,12 +
5 Key UkrCSM 18,585 0,06 0,13 0,03 0,14 +
6 Key INMETRO 18,589 0,05 0,09 0,03 0,11 +
7 Key INTI-1 18,606 0,05 0,10 0,05 0,12 +
8 Key SP 18,655 0,03 0,05 0,10 0,08 -
median 18,560 0,03 0,05 КСRV
mean 18,564 0,02 0,04
weighted mean 18,588 0,01 0,03
Consistency test Conclusion
2
obs

2
0.05,m 1 
m
2 2
0.05,m 1obs  

14.02 2.2 8 inconsistent

Figure 2 Error bars show standard uncertainty. The solid and dashed horizontal lines are the median and upper and low limits of the corresponding
standard uncertainty, respectively.

Figure 3 Degrees of equivalence di and expanded uncertainty U（di）(k=2)




-0,25
-0,20
-0,15
-0,10
-0,05
0,00
0,05
0,10
0,15
0,20
0,25
INACAL LATU MSL UNIIM UkrCSM INMETRO INTI-1 SP
d
i
(%
)

7.4 Discussion

Taking into account the final results it’s possible to say that measurement results of almost
all participants are consistent between each other.

8 EQUIVALENCE STATEMENTS

The equivalence statements have been calculated according to the BIPM guideline. The
degree of equivalence (and its uncertainty) between a NMI result and the KCRV is calculated
according to the following equations:

i i refd x x 
, (16)

      2 22i i refU d u x u x 
, (17)
where
id
is the degree of equivalence between the NMI result xi and the KCRV xref , and
U (di ) is the expanded uncertainty (k = 2) of the
id
calculated by combining the standard
uncertainty u(di ) of the NMI result xi and the standard uncertainty u xref of the KCRV xref (it is
supposed that
 cov ,i refx x
is ineligible). The equivalence statements for CCQM-K130 are given
in Table 10 and Figures 2, 3.

9 CONCLUSIONS

The Median is proposed for the KCRV. The use of median are agreed by all participants.
This Key comparison can be used in order to support calibration and measurement capabilities
in determination of nitrogen mass fraction in glycine and other aminoacids with nitrogen in
amino group (during decomposition by the Kjeldahl method). This Key comparison can’t be
used in order to support calibration and measurement capabilities in determination of nitrogen
mass fraction in compounds with nitrogen in other forms, where additional proof of
applicability is necessary.

10 ACKNOWLEDGEMENTS
UNIM gratefully acknowledges the help and collaboration from LATU, MSL, UNIIM,
UkrCSM, INMETRO, INTI-1, SP, INACAL.

11 REFERENCES
1. Moore, J.C. Total protein methods and their potential utility to reduce the risk of food
protein adulteration / J.C. Moore, W.Vries, M. Lipp, J.C. Grifiths, D.R. Abernethy // Compr. Rev.
Food Sci. F. —2010. — Vol. 9. — Issue 4. — P. 330–351
2. CCQM Guidance note: Estimation of a consensus KCRV and associated Degrees of
Equivalence. Version: 10.

Appendix A – Technical Protocol
CCQM-K130/ CCQM-P166
Nitrogen mass fraction measurements in glycine

1. Introduction
Mass fraction of nitrogen is very important pointer because the results of these
measurements are often used for determination of protein mass fraction that is an important
indicator of the quality of the vast majority of food products and raw materials.
After discussing results of Pilot comparisons in the field of nitrogen mass fraction in dry
milk powder on the session TC 1.8 "Physical Chemistry" COOMET it was decided to offer to
carry out and Key comparisons "Nitrogen mass fraction measurements in glycine" - amino acetic
acid, as the representative of high-purity substances.
The comparison is being carried out for the purpose of the confirmation of follow
measurement capacity:



2. Measurand and reporting
Mandatory measurand (for CCQM-K130) – value of mass fraction of nitrogen.
The aim of CCQM-K130 / CCQM-P166 is to measure mass fraction of nitrogen in
glycine.
Each participant shall report the results for the value of of mass fraction of nitrogen. The
results should be reported in mass fractions, accompanied by a full uncertainty statement
(including a combined standard uncertainty and an expanded uncertainty with a coverage factor
applied). In addition the report should include technical details on the measurement procedure,
traceability links and uncertainty contributions.

3. Guidance values and target uncertainty
Analyte / matrix: the objects of comparisons are nitrogen mass fraction in glycine.
Sample of glycine in the range nitrogen mass fraction from 18,47 % to 18,85 % and in the
range of moisture less than 0,05 % is delivered by UNIIM.
Target uncertainty is expected on the level of 0,1 %.

4. KCRVs
Processing of obtained measurement results of nitrogen mass fraction will be carried out
according to the following articles:
- Cox M.G. “The evaluation of key comparison data”
- Jorg W.Muller. “Possible Advantages of a Robust Evaluation of Comparisons”
It’s offered to try different approaches: the arithmetic mean, weighted mean, median for
the evaluation of reference value.
The reference is invited to try out different ways: the arithmetic mean, weighted mean,
median, etc.

5. Methods of measurement
Each participant may use any suitable method(s) for the measurement of the mass fraction
of nitrogen.

6. Planned time schedule
call for participants: by end of April 2015
latest registration of participant: by end of July 2015 (updated)
latest arrival of samples at participants: by end of September 2015
latest report of results: by end of February 2016
report A: by end of May 2016
report B: by end of July 2016

7. Samples
Sample of glycine in the range nitrogen mass fraction from 18,47 % to 18,85 % and in the
range of moisture less than 0,05 % is delivered by UNIIM.
Packaging and labeling:
The material of the sample is a reagent of aminoacetic acid with a mass fraction of the
basic substance of at least 99,5 %, which is a white powder, packed in dark glass vial, fitted with
a sealed screw caps. Jars further sealed in waterproof bag made from polyethylene. Mass of glycine
in one vial is 5 g. The package has the label with the sample name.
Storage conditions:
- Ambient temperature, °C 20±5
- Protection from the straight sun light
Storage life is 2 years.
Note: After opening the package the samples are selected for the measurement of mass
fractions of nitrogen, the remaining portion of the sample material must not be stored.
Before carrying out the measurements, the package integrity is checking by means of
visual observation. The package is opened and samples are selected.


8. Pilot laboratory
Laboratory of metrology of moisture measurement and certified reference material (241)
NMI’s name and abbreviation
Ural Scientific Research Institute for Metrology, ROSSTANDART, Ekaterinburg (UNIIM)
The postal address: 4, Krasnoarmeiskaya St., Ekaterinburg, Russian Federation, 620000

Head of Laboratory 241, Maria Medvedevskikh
Telephone / Fax +7 (343) 350-60-63, 355-02-63
E-mail: Mariya.medvedevskikh@somet.ru

Research scientist lab. 241 Maria Krasheninina
Telephone / Fax +7 (343) 350-60-63, 355-02-63
E-mail: krasheninina_m@uniim.ru


9. References
1. Cox M.G. “The evaluation of key comparison data”, Metrologia 39 (2002) 589-595
2. Jorg W.Muller. “Possible Advantages of a Robust Evaluation of Comparisons”, Journal
of Research of the National Institute of Standards and Technology Vol.105, No.4 (2000)
551-555