Determination of gold in precious alloys by glow discharge atomic emission spectrometry

Abstract

The increasing need for harmonization in the determination of trace and matrix elements in precious metals and alloys requires the development of innovative and reliable techniques which might eventually replace the conventional fire assay approach. Three types of alloys of Au, with Ag, Cu and Zn (respectively, 910, 750 and 580‰, i.e., 22, 18 and 14 karats), were taken into account. Samples were shaped as flat disks and analyzed for their Au content by glow discharge atomic emission spectrometry (GD-AES). Wherever possible, use was made of Ag or Cu as the internal standard. The discharge conditions adopted included pulsed current intensity in the range 4–9 mA, voltage between 600 and 700 V and Ar pressure of 200 Pa. The concentration values obtained for Au agree well with the nominal concentrations given by the producer for different lots of alloys, as well as with the data obtained by the fire assay. In particular, in terms of accuracy the GD-AES approach appears to be fully equivalent to the fire assay. Repeatability of measurements was also satisfactory, although it should be improved to comply with current regulations, which require an uncertainty range not exceeding 1‰. Inductively coupled plasma atomic emission spectrometry (ICP-AES), on the other hand, appears to be not so suitable for this application.