Overview
ISO 19919:2025 - Jewellery and precious metals - Determination of silver - ICP-OES method using an internal standard element specifies an analytical procedure for accurate measurement of silver content in homogeneous precious-metal materials. The method is optimized for silver fineness from 50 ‰ to 990 ‰ (parts per thousand); higher fineness (>990 ‰) is addressed by spectroscopy-by-difference methods (see ISO 15096). The technique uses inductively coupled plasma optical emission spectrometry (ICP‑OES) with an internal standard to correct for instrument drift and matrix effects.
Key topics and technical requirements
- Scope and sample range: Preferable silver content 50 ‰–990 ‰; lower contents can also be analysed.
- Sample preparation: Weigh at least two accurately known test portions (example ~100 mg), dissolve in nitric acid, precipitate with concentrated hydrochloric acid, re‑dissolve and make up to measurement volume.
- Internal standards: Use single‑element standards such as yttrium, scandium, indium, germanium or lutetium; typical stock concentrations suggested (e.g., ~300 mg·L⁻¹ for In/Lu/Ge, ~100 mg·L⁻¹ for Sc/Y) and added in a fixed mass to all solutions.
- Calibration and bracketing: Bracketing calibration uses two calibration solutions that bracket the sample concentration (recommended preliminary check with three calibration standards). Measurement sequence example: low standard – sample – high standard – sample – low standard – …
- Instrumentation and performance: ICP‑OES capable of simultaneous measurement of Ag and internal standard with minimum optical resolution 0.02 nm. Use high‑purity argon (≥99.995 %), grade‑A volumetric flasks and an analytical balance with 0.01 mg readability.
- Quality criteria: Recommended linearity check (regression coefficient >0.9999) and final relative standard deviation (RSD) ≤ 0.3 % after calculation. Choose emission lines free from spectral interference (recommended wavelengths listed in the standard).
Applications and who uses it
ISO 19919:2025 is intended for:
- Assay offices and analytical laboratories performing silver determination in jewellery, bullion and precious‑metal alloys
- Jewellery manufacturers and quality control teams verifying fineness and material conformity
- Precious metals refineries and traders requiring traceable, reproducible results for certification and trade
Benefits include improved accuracy through internal standardization, robust matrix correction, and traceable calibration suitable for regulatory and commercial reporting.
Related standards
- ISO 15096 - spectroscopy method by difference for very high fineness (>990 ‰)
- ISO 11596 - sampling of precious metals and alloys (referenced for sampling procedures)
Keywords: ISO 19919:2025, ICP‑OES, silver determination, jewellery and precious metals, internal standard, fineness, calibration, analytical method.
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