Internal Standard Method for the Determination of Au and some Platinum Group Metals Using Inductively Coupled Plasma Optical Emission Spectrometry

Abstract

A method is described for the determination of Au, Pt, Pd, Ru and Rh in a converter matte sample, using inductively coupled plasma optical emission spectrometry (ICP-OES), with Y or Sc as internal standard. The results obtained by this method are discussed and compared with values obtained by an independent laboratory. The efficiency of internal standardization was evaluated by varying the operating conditions of the ICP-OES. Changes in the amount of energy transferred from the plasma to analyte, the amount of aerosol reaching the plasma and analyte residence time, were studied in terms of their effect on the emission intensity of the analyte and the internal standard. It was found that changes in the emission signals of the PGMs due to power variations could be effectively compensated for, using either Sc, Y or Ar lines as internal standards. For variations in aerosol gas flow rate, both Sc and Y could only compensate for Pd and Au between flow rates of 0.60 and 0.80 l min -1 and for Pt, Ru and Rh at 0.80 l min -1. The effect of sodium on the determination of Au and the PGMs, and the use of Sc and Y as internal standards, to compensate for Na matrix effects on accuracy were also studied. It was found that emission intensities of the analytes decreased with increasing Na concentration. Furthermore, Sc as an internal standard could compensate for Pt, Ru and Rh up to 5 g l-1 Na, while Y could only compensate for the same elements up to 1 g l -1 Na.


South African Journal of Chemistry Vol.55 2002: 72-86