ISO 19051:2015

INTERNATIONAL ISO
STANDARD 19051
First edition
2015-05-01
Rubber, raw natural, and rubber latex,
natural — Determination of nitrogen
content by Micro Dumas combustion
method
Latex de caoutchouc brut — Détermination de la teneur en azote par
la méthode de combustion de Micro Duma
Reference number
ISO 19051:2015(E)
©
ISO 2015

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ISO 19051:2015(E)

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ISO 19051:2015(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Principle . 1
4 Reagents . 2
5 Apparatus . 2
6 Calibration . 3
7 Sampling and preparation of test piece . 3
8 Procedure. 4
9 Test report . 5
Annex A (normative) Calibration schedule . 7
Annex B (informative) Technical justification of Micro Dumas combustion process .8
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ISO 19051:2015(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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electrotechnical standardization.
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described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
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The committee responsible for this document is ISO/TC 45, Rubber and rubber products, Subcommittee
SC 2, Testing and analysis.
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ISO 19051:2015(E)

Introduction
The Dumas combustion method has become the most frequently used method worldwide for the accurate
and fast determination of nitrogen. Compared to the wet chemical Kjeldahl method, it is superior in
terms of speed, safety, and environmental friendliness. The representative analysis of a natural product
requires a larger sample size of up to 1 g or more.
The nitrogen content of natural rubber is related to the protein level. The protein content of natural
rubber varies depending upon its source and methods used in its processing. Generally, raw natural
rubber is expected to have a nitrogen content in the range of 0,3 % to 0,6 %. The normal latex grades
have lower levels of nitrogen than the “dry” rubbers, with values around 0,2 %. However, “skim” rubber,
with its high protein content, will have appreciably higher values, in the range of 1,5 % to 2,5 %.
This test method will help determine the nitrogen content of the raw natural rubber in the shortest
possible time and will be helpful for laboratory quality control testing.
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INTERNATIONAL STANDARD ISO 19051:2015(E)
Rubber, raw natural, and rubber latex, natural —
Determination of nitrogen content by Micro Dumas
combustion method
WARNING 1 — Persons using this International Standard should be familiar with normal
laboratory practice. This International Standard does not purport to address all of the safety
problems, if any, associated with its use. It is the responsibility of the user to establish appropriate
safety and health practices and to ensure compliance with any national regulatory conditions.
WARNING 2 — Certain procedures specified in this International Standard might involve the use
or generation of substances or the generation of waste that could constitute a local environmental
hazard. Reference should be made to appropriate documentation on safe handling and disposal
after use.
1 Scope
This International Standard specifies a test method for the determination of nitrogen content of raw
natural rubber using the Micro Dumas combustion method. This method is also applicable to natural
rubber latex.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 123, Rubber latex — Sampling
ISO 124:2014, Latex, rubber — Determination of total solids content
ISO 1795, Rubber, raw natural and raw synthetic — Sampling and further preparative procedures
ISO 18899:2013, Rubber — Guide to the calibration of test equipment
3 Principle
In the combustion process (furnace at ca. 1 000 °C), nitrogen is converted to nitrogen gas/oxides. If
other elements are present, they will also be converted to different combustion products. A variety of
absorbents are used to remove these additional combustion products.
The combustion products are swept out of the combustion chamber by an inert carrier gas such as
helium and passed over heated (about 600 °C) high purity copper. This copper can be situated at the
base of the combustion chamber or in a separate furnace. The function of this copper is to remove any
oxygen not consumed in the initial combustion and to convert any oxides of nitrogen to nitrogen gas.
The gases are then passed through the absorbent traps.
Detection of the gases can be carried out in a variety of ways, including the following:
a) GC separation followed by quantification using thermal conductivity detection;
b) partial separation by GC (“frontal chromatography”) followed by thermal conductivity detection;
c) series of separate infrared and thermal conductivity cells for detection of individual compounds.
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ISO 19051:2015(E)

Quantification of nitrogen requires calibration with high purity “micro-analytical standard” standard
reference compounds with known nitrogen content.
During the combustion process, organic compounds are oxidized at high temperature to yield carbon
dioxide, water, and oxides of nitrogen:
O;1000°C
2
CHNCompoundC→ OH++ONO
22 x
The oxides of nitrogen are then converted to nitrogen gas in the presence of metallic copper:
Cu;600°C
NO → N
x 2
4 Reagents
4.1 Helium (99,99 %), as carrier gas and high purity (99,99 %) oxygen as combustion gas.
4.2 Analytical standards, as per Table 1.
Table 1 — Reference standards
Sample Molecular formula Theoretical %C Theoretical %H Theoretical %N Theoretical %S
Tryptophan C H N O 64,69 % 5,92 % 13,72 % 0 %
11 12 2 2
Imidazole C H N 52,93 % 5,92 % 41,15 % 0 %
3 4 2
Isatin C H NO 65,31 % 3,43 % 9,52 % 0 %
8 5 2
Alanine C H NO 40,44 % 7,92 % 15,72 % 0 %
3 7 2
Nicotinamide C H N O 59,01 % 4,95 % 22,94 % 0 %
6 6 2
Lysine C H N O 49,30 % 9,65 % 19,16 % 0 %
6 14 2 2
Cyclohexanone C H O 73,43 % 10,27 % 0 % 0 %
6 10
Acetanilide C H NO 71,09 % 6,71 % 10,36 % 0 %
8 9
Urea CH N O 20,00 % 6,71 % 46,65 % 0 %
4 2
Atropine C H NO 70,56 % 8,01 % 4,84 % 0 %
17 23 3
Cystine C H N O S 29,99 % 5,03 % 11,66 % 26,69 %
6 12 2 4 2
Sulphanilamide C H N O S 41,84 % 4,68 % 16,27 % 18,62 %
6 8 2 2
BBOT C H N O S 72,53 % 6,09 % 6,51 % 7,44 %
26 26 2 2
5 Apparatus
5.1 Combustion elemental analysers are manufactured in a variety of configurations to suit specific
applications and the choice will depend on the elements of interest, the sample type and size, and the
concentration of the analyte.
All instruments require two gas supplies: an inert carrier gas (helium recom
...