ISO 4941:2024

Overview

ISO 4941:2024 - Steel and iron - Determination of molybdenum content - Thiocyanate spectrophotometric method - specifies a validated laboratory procedure for measuring molybdenum (Mo) content in steel and iron. The standard covers sample dissolution, formation of a thiocyanate-based coloured complex, organic extraction and spectrophotometric measurement (around 470 nm) for Mo mass fractions between 0.005 % and 0.125 %. This is the third edition, technically revised from the 1994 version.

Key topics and requirements

• Scope and applicability: Measurement range 0.005–0.125 % Mo in steel and iron.
• Analytical principle: Dissolve sample, oxidize carbides, form a molybdenum–thiocyanate coloured complex, extract into butyl acetate, and measure absorbance at ~470 nm.
• Interferences: Vanadium and tungsten interfere when V/Mo > 16 or W/Mo > 8; the standard documents how these affect results.
• Reagents & standards: Specifies analytical-grade reagents and prepared solutions (acid mixtures, ammonium thiocyanate, L(+)-ascorbic acid, copper(II) solutions, tin(II)-copper(II) chloride, Mo standard solutions).
• Apparatus: Requires class A glassware, a separating funnel (100 ml) and a spectrophotometer with 10 mm or 20 mm optical path length cells.
• Procedure highlights: Typical test portion ≈ 1.00 g; use ISO 14284 for sampling/preparation; steps include test and compensating solutions, extraction of the organic layer, and calibration curve establishment.
• Safety: Warning on perchloric acid vapour - explosion hazard in presence of organics, ammonia or nitrous fumes.
• Quality control: Calibration curve preparation, use of compensating solution (pure iron) to correct background absorption, and updated precision data included.

Applications

ISO 4941:2024 is intended for:

• Steel and iron producers for alloy certification and process control.
• Metallurgical and chemical testing laboratories performing routine compositional analysis.
• Quality assurance teams verifying conformity to material specifications.
• R&D and failure analysis where accurate Mo quantification is required for metallurgical interpretation.

Practical uses include quality control of Mo-bearing steels, verification of supplier material certificates, and traceability in analytical records.

Related standards

• ISO 14284 - Sampling and preparation of samples for chemical composition determination
• ISO 3696 - Water for analytical laboratory use
• ISO 385 / ISO 648 / ISO 1042 - Laboratory glassware (burettes, pipettes, volumetric flasks)
• ISO 4800 - Separating funnels

Keywords: ISO 4941:2024, molybdenum determination, thiocyanate spectrophotometric method, steel and iron analysis, spectrophotometry, Mo content, interference V/Mo W/Mo, calibration curve.