Overview
ISO 15093:2020 specifies an analytical procedure for the determination of high‑purity gold, platinum and palladium using the difference method with ICP‑OES (inductively coupled plasma optical emission spectrometry). The standard covers alloys and samples with a nominal fineness of 999 ‰ and above, with specific modifications in Annex B for fineness ≥ 999.9 ‰. It is the recommended method for assaying precious metals in jewellery and related products.
Key topics and technical requirements
- Principle: dissolve a weighed sample in aqua regia to prepare a ~10 g·L⁻¹ solution (higher concentration for ≥999.9 ‰), determine impurity elements by ICP‑OES, and calculate precious metal fineness by subtracting total impurities from 1 000 ‰.
- Instrumentation: ICP‑OES with minimum optical resolution 0.02 nm, detection limit 0.02 mg·L⁻¹, and background correction capability.
- Reagents & calibration:
- Use analytical grade acids (HCl, HNO3) and freshly prepared aqua regia.
- Stock solutions (A–D) of impurities are defined for calibration; reference materials of at least 999.9 ‰ purity are required to account for impurities introduced by standards.
- Multi‑point calibration and blank correction required; calibration curves per element are used to convert net intensities to concentrations.
- Sample prep & measurement:
- Typical sample: (500 ± 10) mg dissolved, heated to expel nitrogen oxides, made to 50 mL.
- Two independent sample solutions per sample; duplicate determinations should agree within 10% for the sum of impurities.
- Measurement conditions include stabilization time, multiple integrations and adequate rinsing between runs.
- Results & reporting:
- Express precious metal content in parts per thousand (‰) with four significant figures.
- Test report must document sample ID, sampling method (per ISO 11596), method reference (ISO 15093:2020), deviations, and laboratory identifiers.
Applications and users
- Routine and forensic assay laboratories for jewellery, bullion and precious metal products.
- Refineries, hallmarking authorities, quality control labs and regulatory bodies verifying fineness of gold, platinum and palladium.
- Useful for manufacturers and purchasers requiring traceable, standardized determination of high‑purity precious metals using ICP‑OES.
Related standards
- ISO 11596 - Jewellery - Sampling of precious metal alloys (referenced normative standard).
- ISO 15096 - structural alignment noted in ISO 15093 foreword (related document structure).
Keywords: ISO 15093:2020, ICP‑OES difference method, high purity gold, platinum, palladium, fineness 999 ‰, aqua regia dissolution, calibration, precious metals assay.
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