BS ISO 7431-1:2024
Thiourea for industrial use - Test methods

Standard No.

BS ISO 7431-1:2024

Release Date

2024

Published By

British Standards Institution (BSI)  GB  /  BSI

Latest

BS ISO 7431-1:2024

Introduction

Standard Framework and Technological Evolution

BS ISO 7431-1:2024, as the latest international standard for the industrial application of thiourea, integrates modern analytical techniques such as ion chromatography (IC) and inductively coupled plasma optical emission spectroscopy (ICP-OES). Compared with the previous version, the main updates are as follows:

Technical dimension	ISO 7431-1:2024	Traditional method
Calcium detection	New ICP-OES method (LOD 0.01mg/L)	Atomic absorption method only
Thiocyanate determination	Ion chromatography (ISO 10304-3)	Colorimetry
Heavy metal detection	Sodium sulfide-glycerol colorimetric method (Pb≤0.001%)	Unspecified limit

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Analysis of core test methods

4.2 Determination of thiourea content (iodine titration)

Automatic titrator undergoes redox reaction with iodine under alkaline conditions, key parameters:

• Reaction equation: 4NaIO + CS(NH₂)₂ + H₂O → CO(NH₂)₂ + 4NaI + H₂SO₄
• Titration endpoint: The blue color of starch indicator disappears
• Tolerance: Absolute difference of parallel determination ≤0.2%

4.8 Calcium detection (arbitration method)

When using atomic absorption spectroscopy (AAS) as an arbitration method, please note:

1. Sample pretreatment: carbonization at 850±25℃
2. Dissolution in nitric acid medium (pH<2)
3. Characteristic wavelength: 422.7nm

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Implementation suggestions

Application case of rubber additive industry

When a rubber factory uses this standard to detect thiourea used as a vulcanization accelerator:

• Ignition residue must be controlled at ≤0.02% (Clause 4.4)
• Heavy metal detection adopts the comparative solution method (Clause 4.9)
• It is recommended to add XRF screening as a rapid initial screening method

Precautions for implementation of the standard

• Safety warning: Thiourea is toxic by skin absorption (CAS 62-56-6)
• Pure water requirements: meet ISO 3696 grade 3 water standards
• Sampling specifications: follow ISO 8213 solid chemical sampling standards

BS ISO 7431-1:2024 Referenced Document

• ISO 10304-3:1997 Water quality - Determination of dissolved anions by liquid chromatography of ions - Part 3: Determination of chromate, iodide, sulfite, thiocyanate and thiosulfate
• ISO 11885:2007 Water quality - Determination of selected elements by inductively coupled plasma optical emission spectrometry (ICP-OES)
• ISO 14911:1998 Water quality - Determination of dissolved Li<(hoch)+>, Na<(hoch)+>, NH<(Index)4><(hoch)+>, K<(hoch)+>, Mn<(hoch)2+>, Ca<(hoch)2+>, Mg<(hoch)2+>, Sr<(hoch)2+> and Ba<(hoch)2+> using ion chromatography - Method for water and waste water
• 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; Determination of calcium and magnesium; Atomic absorption spectrometric method
• ISO 8213 Chemical products for industrial use; Sampling techniques; Solid chemical products in the form of particles varying from powders to coarse lumps

BS ISO 7431-1:2024 history

• 2024 BS ISO 7431-1:2024 Thiourea for industrial use - Test methods

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