ISO 7431-1:2024

International
Standard
ISO 7431-1
First edition
Thiourea for industrial use —
2024-01
Part 1:
Test methods
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test methods . 2
4.1 General .2
4.2 Determination of thiourea content.2
4.2.1 Principle .2
4.2.2 Reagents .2
4.2.3 Apparatus .2
4.2.4 Procedure .3
4.2.5 Calculation .3
4.2.6 Expression of results .3
4.3 Determination of water insoluble substance .3
4.3.1 Principle .3
4.3.2 Apparatus .3
4.3.3 Procedure .4
4.3.4 Calculation .4
4.3.5 Expression of results .4
4.4 Determination of ignition residue .4
4.4.1 Principle .4
4.4.2 Apparatus .4
4.4.3 Procedure .4
4.4.4 Calculation .4
4.4.5 Expression of results .5
4.5 Determination of initial melting point .5
4.5.1 Principle .5
4.5.2 Apparatus .5
4.5.3 Procedure .5
4.5.4 Calculation .5
4.5.5 Expression of results .5
4.6 Determination of turbidity .5
4.7 Determination of thiocyanate content .5
4.7.1 Principle .5
4.7.2 Reagents .6
4.7.3 Apparatus .6
4.7.4 Procedure .6
4.7.5 Calculation .6
4.7.6 Expression of results .6
4.8 Determination of calcium element .6
4.8.1 General .6
4.8.2 Ion chromatography .6
4.8.3 Inductively coupled plasma optical emission spectrometry (ICP-OES) .7
4.8.4 Atomic absorption spectrometry (AAS) (referee method) .8
4.9 Determination of heavy metals .9
4.9.1 Principle .9
4.9.2 Reagents .9
4.9.3 Apparatus .9
4.9.4 Procedure .9
4.9.5 Determination .9
4.9.6 Expression of results .9

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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The procedures used to develop this document and those intended for its further maintenance are described
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This document was prepared by Technical Committee ISO/TC 47, Chemistry.
A list of all parts in the ISO 7431 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
Introduction
1)
Thiourea (CAS No. 62-56-6), as a kind of chemical raw material, is widely used in the manufacture of drugs,
dyes, resins, compression plastic powder, etc., and can also be used as vulcanization accelerator for rubber
and flotation agent for metal minerals, especially in the field of high-folding optical resin materials.
Thiourea molecular weight: 76,12 (according to international relative atomic mass of 2019)
1) Chemical Abstracts Service (CAS) Registry Number® is a trademark of the American Chemical Society (ACS). This
information is given for the convenience of users of this document and does not constitute an endorsement by ISO of the
product named. Equivalent products may be used if they can be shown to lead to the same results.

v
International Standard ISO 7431-1:2024(en)
Thiourea for industrial use —
Part 1:
Test methods
WARNING — Thiourea is environmental hazard and toxic by ingestion and skin absorption to
humans. It is the responsibility of the users of this document to establish appropriate safety and
health practices and determine the applicability of regulatory limitations prior to use.
1 Scope
The document specifies test methods for industrial thiourea properties, such as thiourea content, water
insoluble substance, ignition residue, initial melting point, turbidity, thiocyanate content, calcium element
and heavy metals.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 3165, Sampling of chemical products for industrial use — Safety in sampling
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 6353-1:1982, Reagents for chemical analysis — Part 1: General test methods
ISO 7027-1, Water quality — Determination of turbidity — Part 1: Quantitative methods
ISO 7980:1986, Water quality — Determinati
...