ISO 15096:2020 download.Jewellery and precious metals Determination of high purity silver Difference method using ICP-OES.
ISO 15096 specifies the analytical procedure for the determination of silver with a nominal content of and above 999 %o (parts per thousand).
ISO 15096 specifies a method intended to be used as the recommended method for the determination of silver of fineness of and above 999 %o. For the determination of fineness of and above 999,9 %o, modifications described in Annex B apply.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 11596,Jewellery — Sampling of precious metal alloys for and in jewellery and associated products
3 Terms and definitions
No terms and definitions are listed in ISO 15096.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
The sample is weighed and dissolved in nitric acid to prepare a 10 g/l solution (higher concentration is used for fineness of and above 999,9 %o). The suspension, which can be present in that solution, is isolated by centrifugation or microfiftration and dissolved in aqua regia. Both nitric and aqua regia solutions are analysed separately by ICP-OES and the total content of each impurity (see Table A.1 for wavelengths) in the sample is obtained by adding together the results of the two analyses. The silver content is obtained by subtraction of the total content of impurities in the sample from 1 000 %o. For the determination of fineness of and above 999,9 %o, modifications described in Annex B shall be applied.
5 Reagents
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity.
5.1 Hydrochloric acid (HC1), 30 % to 37 % HCI (mass fraction).
5.2 Nitric acid (H NO3), 65 % to 70 % HNO3 (mass fraction).
5.3 Aqua regia (should be prepared just before use). Mix three volumes of hydrochloric acid (5.1) and one volume of nitric acid (5.2).
5.5 Stock solution B (shall not contain any chloride), Ni, Sb, Se, Te, Ti (100 mg/I each) in 3 % to 7 % HNO3 (52) (mass fraction).
5.6 Stock solution C (shall not contain any chloride), As, Bi, Co, Pb, Pt, Si, Sn, Zn (100 mg/i each) in
3 % to 7 % HNO3 (52) (mass fraction).
5.7 Stock solution D (shall not contain any chloride), Ga, Ge, Hg. In, Pd, TI (100 mg/I each) in 3 % to 7 % HNO3 (52) (mass fraction).
NOTE 1 Elements which do not need to he analysed can be omitted. Other elements can be added, provided they are stable and do not generate significant interferences.
NOTE 2 Stock solutions “A” to D are typically prepared by mixIng 10 % (of the total volume) of each
1 000 mg/I monoelemental solution with 5 % of nitric acid (5.2) (volume fraction) and making up with water.
They can be kept [or up to 12 months under proper storage conditions.
5.8 Stock solution E (may contain both chlorides and nitrates), Al, Au, Cr. Fe, Mg, Ni, Pt, Sn (100 mg/I each) in 3 % to 7 % aqua regia (i3) (volume fraction).
NOTE Stock solution E is typically prepared by mixing 10 % (of the total volume) of each 1 000 mg/I monoelemuntal solution with 5 % of aqua regia (53) (volume fraction) and making up with water. It can be kept for up to 12 months under proper storage conditions.
5.9 Reference materials: silver of 999,9 %o minimum purity The content of each impurity shall be specified and taken into account in the calibration.
6 Apparatus
6.1 Customary laboratory apparatus.
6.2 ICP-OES, with a minimum optical resolution of 0,02 nm, a detection limit of 0,02 mg/I or better, and capability of background correction.
NOTE For preferably used wavelengths, see Annex A.
8.2 Sample solution
For each sample to be analysed, two sample solutions shall be prepared as follows and analysed.
The sample should be etched, washed and dried before use to remove any surface contamination.
Weigh (500 ± 10) mg of the sample portion to the nearest 0,1 mg, transfer into a 50 ml beaker, and add 7,5 ml of H20 and 7,5 ml of HNO3 (12). Heat gently until complete dissolution of the sample and continue to heat to expel the nitrogen oxides. Add 10 ml of water. After cooling to room temperature, transfer the solution from the 50 ml beaker to the centrifuge tube. Centrifuge the mixture at 3 000 r/min for 5 mm and transfer the liquid phase into a 50 ml volumetric flask. Add 5 ml of water to the residue, centrifuge the mixture again at 3 000 r/min for 5 mm more, and add the newly formed liquid phase to the 50 ml volumetric flask. This operation is repeated two extra times. Make up the volume of the volumetric flask water to 50 ml, and mix thoroughly.
Alternatively, after cooling to room temperature, filter the solution through a microfiltration system, add the filtrate to a 50 ml volumetric flask and make up the volume of the solution with water to 50 ml, and mix thoroughly. Analyse this solution without delay using the calibration solutions specified in fl3.
Add 2 ml of freshly prepared aqua regia (5) to the residue after centrifugation or microfiltration (if microfiltration is used, the filter shall be dissolved, too). Heat until complete dissolution and continue to heat to expel the nitrogen oxides. Cool to room temperature, transfer to a 5 ml volumetric flask, rinse with water, and make up with water to 5 ml. Analyse this solution using the aqua regia calibration solutions specified in UA.
8.3 Silver matrix calibration solutions (10 g/l)
Weigh three portions of (500 ± 10) mg of the silver (5.9), and dissolve, cool and transfer into 50 ml volumetric flasks each one as specified in &Z.
8.3.1 Blank solution 1.
Make up with water to 50 ml, and mix thoroughly.

9.3 Repeatability
Duplicate determinations shall give results differing by less than 10 % for the sum of impurities. If the difference is greater than this, the assay shall be repeated.
10 Test report
The test report shall Include at least the following information:
a) identification of the sample including source, date of receipt, and form of sample;
b) sampling procedure;
c) method used by reference to this document, i.e. ISO 15096:2020;
d) precious metals content of the sample, in parts per thousand (%o) by mass, as single values and mean values, with the result reported with four significant figures;
e) if relevant, any deviations from the method specified in this document;
any unusual features observed during the determination;
g) date of test;
h) identification of the laboratory carrying out the test;
i) signature of the laboratory manager and operator.