Overview
ISO 4946:2016 specifies a spectrophotometric method for the determination of copper in steel and cast iron using the 2,2'-biquinoline (cuproine) reagent. The method covers copper mass fractions from 0.02 % to 5.0 %. It describes sample dissolution, fuming with perchloric acid, reduction of Cu(II) to Cu(I), colour development with 2,2'-biquinoline and absorbance measurement at about 545 nm.
Key topics and technical requirements
- Scope & applicability: Quantitative copper determination in steel and cast iron within 0.02–5.0 % mass fraction.
- Principle: Dissolve sample in HCl/HNO3, fume with perchloric acid to remove acids and silica, reduce Cu(II) to Cu(I) with ascorbic acid, form coloured Cu(I)-2,2'-biquinoline complex and measure absorbance at ~545 nm.
- Reagents & standards:
- High‑purity iron (≤ 0.001 % Cu) for blanks and calibration.
- Hydrochloric, nitric and perchloric acids (with safety warnings for perchloric acid).
- Dimethylformamide (DMF) as solvent for 2,2'-biquinoline (warning: DMF is hazardous).
- Ascorbic acid solution (200 g/l) and 2,2'-biquinoline solution (0.60 g/l in DMF).
- Copper standard solutions: 1 g/l and 0.05 g/l for calibration.
- Apparatus & measurement:
- Class A volumetric glassware per ISO 648 & ISO 1042.
- Spectrophotometer set to ~545 nm, cells of 2 cm (or 4 cm for low concentrations).
- Procedure highlights:
- Typical test portion ≈ 0.5 g.
- Aliquot volumes adjusted by expected copper content (e.g., 100 ml test solution with 10 ml aliquot for 0.02–0.3 % Cu).
- Use a compensating solution (DMF instead of 2,2'-biquinoline) to zero the instrument.
- Establish a calibration graph by plotting net absorbance vs. µg Cu per ml; convert measured absorbance to copper mass fraction with blank correction.
- Precision: Method precision was evaluated by an interlaboratory trial (six labs) and analysed according to ISO 5725; repeatability/reproducibility vary with copper content.
Applications and users
ISO 4946:2016 is intended for:
- Metallurgical and materials testing laboratories performing quality control on steel and cast iron.
- Steel producers and foundries monitoring copper content for specification compliance and process control.
- Inspection bodies and laboratories performing official or contractual chemical analysis.
Practical applications include alloy verification, failure analysis and conformity testing where accurate copper quantification is required.
Related standards
- ISO 648 - Single‑volume pipettes
- ISO 1042 - One‑mark volumetric flasks
- ISO 3696 - Water for analytical laboratory use
- ISO 14284 - Sampling and sample preparation for steel and iron
- ISO 5725 - Precision of measurement methods
Keywords: ISO 4946, copper determination, 2,2'-biquinoline, spectrophotometric method, steel and cast iron, metallurgical testing, copper mass fraction, calibration graph, spectrophotometer.
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