ISO 23345:2021 pdf free download – I ewellery and precious metals一Non destructive precious metal fineness confirmation by ED-XRF.
Introduction
This document describes a non-destructive method to verify (confirm) the fineness of finished and semifinished jewellery items considered homogeneous by ED-XRF (energy-dispersive X-ray fluorescence).
Multiple methods are available to determine the fineness of precious metal alloys. They however are all requiring the destruction of the sample and long analysis time; for example gold cupellation by Iso 11426. Under some circumstances, destruction of the sample is not an option. This method proposes a non-destructive alternative, which allows validating a declared fineness.
The standard is not suitable for the regulatory hallmarking application. Because of the inherent higher uncertainty associated with ED-XRF measurements, some results might be inconclusive.
The document gives guidelines on the
— instrumentation,
— number and composition of calibration standards needed for calibration,
— composition of reference material needed to verify the calibration,
— number of measurement and replicates on the sample whose fineness is to be verified
— uncertainty calculation, and
— interpretation of the results.
— known exact composition;
— composition of major and minor elements matching approximatively the sample to be analysed; trace elements may be ignored; a minimum of 3 standards shall be used, with the major element(s) composition covering a range up to 50 %o.
— minor elements below 5 %o do not need to be present in the standards but shall be declared in the calibration; they may be calibrated using the instrument maker’s calibration.
EXAMPLE For the measurement of an alloy with Au = 750 %o, the fineness of Au in the calibration standards may be 730 %o, 750 %o, and 770 %o.
6.1.2 Method calibration
The ED-XRF instrument (51) shall be specifically calibrated for each sample to be analysed. Each standard shall be analysed at least on 5 different positions. The standard deviation obtained for the measurements of each calibration standard shall not exceed 1,2 %o for the major element.
Inter-element interference corrections should be applied.
Analysis of the calibration standards, the reference material and the samples shall be performed using the same collimator size and using the same parameters (tube voltage, current, etc.). The largest possible collimator compatible with the sample target area should be used.
6.2 Verification
6.2.1 Reference material
To verify the calibration, a reference material with the following features shall be used:
— flat and clean surface of suitable size, with at least a diameter 5 times larger than the collimator used for measurement;
— sufficiently thick (at least 0,5 mm);
— homogeneous;
— known exact composition;
— not being used as calibration standard;
— certified reference material (CRM) and materials prepared under the ISO 17034 accreditation areE preferred;
— the composition of the reference material should be matching as far as practicable that of the sample; for major elements there shall be no more than 10 %o absolute difference between the concentration in the sample and in the reference material; for minor elements, that difference shall be no more than 20 %o absolute difference; trace elements may be ignored.
EXAMPLE If an alloy with a 750 %o Au — 240 %o Ag — 10 %o Cu is to be analysed, the concentrations in the reference material are between 740 %o and 760 %o for Au, between 260 %o and 220 %o for Ag, and between 30%oandO%oforCu.
6.2.2 Method verification
Before each batch analysis, the calibration shall be controlled by analysing the reference material.
The reference material shall be analysed at least on 5 different positions. The analysis time for each replicate shall not exceed the time used for the calibration. The standard deviation obtained for the measurements in the reference material shall not exceed 1,2 %o for the major element.