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
Eliane C. P. do Rego,
Metrology, Quality and Technology
INMETRO
Brazil
Wagner Wollinger, Tânia M. Monteiro,
Key
Lucas J. de Carvalho
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
M. Alejandra
Industrial Technology
INTI-1
Argentina Rodriguez, Gabriela
Key
Rodriguez
Laboratorio Tecnológico del Uruguay
LATU
Uruguay
Karino Salvo
Key
State Enterprise All-
Ukrainian State Research
and production Center of
Standardization Metrology, Certification
UkrCSM
Ukraine
Vladimir Gavrilkin, Sergij Kulyk
Key
and Consumers’ Rights
Protection
Measurement Standards Laboratory of New Zealand
MSL
New Zealand
Laly Samuel
Key
Ural Scientific Research
Maria
Institute for Metrology
UNIIM
Russia
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 1
1
18,57
2
18,57
3
18,47
4
18,52
5
18,72
6
18,66
Nitrogen mass fraction, %
2
3
4
18,48 18,53 18,42 18,50 18,50 18,50
18,56 18,51 18,50 18,51 18,52 18,67
18,53 18,56 18,44 18,47 18,55 18,54
5
18,47 18,45 18,53 18,62 18,66 18,46
Mean value in vial, %
18,52 18,52 18,47 18,52 18,59 18,57
In order to estimate the inhomogeneity contribution uh , 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, uh , value for glycine (see Table 3, 4) were calculated according to ISO Guide 35 using the Equations (1) and (2).
uh
MSamong MSwithin n
(1)
uh
MSwithin 4
2
,
n N (n1)
(2)
where N=6, n=5.
Table 3 ANOVA analysis
Vial
number
1
5
2
5
3
5
4
5
5
5
6
5
sum 92,619 92,611 92,363 92,619 92,944 92,833
average 18,524 18,522 18,473 18,524 18,589 18,567
dispersion 0,0022 0,0024 0,0022 0,0031 0,0089 0,0093
Table 4 ANOVA analysis
source
SS
Among
0,040918
Within
0,112078
Sum
0,15299
standard uncertainties due to inhomogeneity, uh
standard uncertainties due to inhomogeneity, uh
relative standard uncertainties due to inhomogeneity, uho
df 5 24 29
0,027
-
0,14
MS 0,008184 0,004670
% %
F 1,7524
Equation (1) Equation (2)
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:
T t1 t0
2 10 ,
(3)
где –time of conducting the experiment, days;
T – estimated shelf life, days;
t1 - temperature of testing of samples (90±5), °C;
t0 - 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
4
21.12.2015
mean of stability test, Xs
18,46 18,70 18,56
standard deviation of the data of key comparison participants, S Xs+S Xs-S slope,b
standard uncertainty of slope, uslope
confidence interval t u 0,05;(n2) slope
standard uncertainty due to long-term (in)stability, us relative standard uncertainty due to long-term (in)stability, uso , % time measurements in key comparison, t, days (according to isochronous experiment)
0,10 18,66 18,46 0,0073 0,0071 0,03 0,67
0,32
360
Nitrogen mass fraction, %
18,90 18,80
W = 0,007333t + 18,450000
18,70
Mean of stability test results - 1S
18,60
18,50 18,40
Mean of stability test results - 1S
18,30
18,20
0
1
2
3
4
5
Time, mounth
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:
us uslope 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).
Table 6 Sample sent dates, receipt dates and report dates
Institute
Sample dispatch date Sample receipt date
INMETRO
19 August 2015
28 August 2015
INACAL
19 August 2015
23 November 2015
SP
19 August 2015
2 September 2015
INTI-1
19 August 2015
16 September 2015
LATU UkrCSM
MSL
19 August 2015 19 August 2015 19 August 2015
26 August 2015 2 September 2015 2 September 2015
Date report sent 29.02.2016 29.02.2016 29.02.2016 29.02.2016 10.03.2016 29.02.2016 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
INMETRO
Method of analysis
Kjeldahl
Approx. sample mass, g
0,7
Titrant, its molar concentration
Sulphuric acid 0,25 M
INACAL
Kjeldahl
0,500±0,005
Hydrochloric acid, 0,1 M
SP
Elemental method
0,035
-
INTI-1 LATU UkrCSM
Kjeldahl Kjeldahl Kjeldahl
0,130±0,007 0,155±0,005
0,15±0,1
Hydrochloric acid, 0,1 M
Hydrochloric acid, 0,1 M
Sulphuric acid 0,05 M
MSL UNIIM
Kjeldahl Kjeldahl
0,15 0,16±0,1
Hydrochloric acid, 0,1 M
Sulphuric acid 0,05 M
Table 8 Traceability details
Institute
Traceability
INMETRO INACAL
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. 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 UkrCSM
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. 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 UNIIM
Traceability is provided by using: -NMIJ CRM3201-a05- 0.1mol/kg HCl traceable to SI and certified by coulometric titration. 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
Type A - repeatability of measurement results
INMETRO
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
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
SP
- 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
Type A - repeatability of measurement results.
INTI-1
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)
UkrCSM MSL UNIIM
- 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
Type A - repeatability of measurement results
Type B - sample weighting - EP determination - titrant volume determination - titrant concentration determination - nitrogen atomic mass uncertainty
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
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 xi and associated uncertainties u xi has been carried out
in accordance with CCQM guidance note [2] using the following equation
xi med (x) ,
(5)
u(xi )
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).
m
xu
xi / u2 xi
m
,
(6)
i1 1/ u2 xi
i 1
2 obs
m i 1
xi u
xu xi
2
,
(7)
where xi - 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 obs
m 1,
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
m 1
2 obs
2 0.05,m1
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 obs
2 0.05,m1
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.
x
1 m
m i 1
xi
,
(8)
m
xi x 2
ux
i 1
mm 1
,
(9)
where xi - result of value of i NMI, u x - standard uncertainty of x .
Uncertainty-weighted mean
m
xu wi xi ,
(10)
i 1
wi
1/ u2 xi
m
,
(11)
1/ u2 xi
i 1
u2
1
xu
m
1/ u2 xi ,
i 1
(12)
where u xi - standard uncertainty of xi .
Median
med
x
1 2
xm /2
xm /21
,
even
m
even
,
(13)
xm1/2 ,
m odd
u2 med x 2 ,
(14)
2m
1.483med di ,
(15)
where di xi 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
obs
0.05,m1
in this case the data is mutually inconsistent,
The reported uncertainties are not very different,
There two extreme values according to xi med x / u xi ,
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
№ comparison
NMI/ DIS
Nitrogen mass
fraction, %
Combined standard uncertainty,
uc, %
12
3
4
5
1 Key INACAL 18,508
0,04
2 Key LATU
18,513
0,07
3 Key
MSL
18,524
0,09
4 Key UNIIM
18,535
0,05
5 Key UkrCSM 18,585
0,06
6 Key INMETRO 18,589
0,05
7 Key INTI-1
18,606
0,05
8 Key
SP
18,655
0,03
median mean
18,560
0,03
18,564
0,02
weighted mean
18,588
0,01
Consistency test
2 obs
2 0.05, m 1
14.02
2.2
Expanded uncertainty, U(k=2), %
6 0,07 0,13 0,17 0,11 0,13 0,09 0,10 0,05 0,05 0,04 0,03
m
8
di, %
U(di), % Verdict
7
8
9
-0,05
0,09
+
-0,05
0,14
+
-0,04
0,18
+
-0,03
0,12
+
0,03
0,14
+
0,03
0,11
+
0,05
0,12
+
0,10
0,08
-
КСRV
Conclusion
2
2
obs
0.05,m1
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.
di (%)
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
Figure 3 Degrees of equivalence di and expanded uncertainty U（di）(k=2)
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:
di xi xref ,
(16)
U di 2 u2 xi u2 xref ,
(17)
where di 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 di 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 xi , xref 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: latest registration of participant: latest arrival of samples at participants: latest report of results: report A: report B:
by end of April 2015 by end of July 2015 (updated) by end of September 2015 by end of February 2016 by end of May 2016 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
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