Comparison of interferences and matrix modifiers in the determination of gold by electrothermal atomisation atomic absorption spectrometry with Zeeman-effect background correction

Interference effects caused by percent. levels of NaCl, MgCl2, CaCl2, Mg(ClO4)2, HNO3, HCl and HCIO4 in the determination of Au by ETA-AAS were compared for tube-wall and platform atomisation. The effectiveness of various matrix modifiers in reducing the interferences was also assessed. The modifiers used were Ni, Pd, Pd-Mo, Cu, or Pd-Mo-Ni for wall atomisation and Ni or Pd-Mo for platform atomisation. All the modifiers increased the char temperature for Au from 800–900 °C to 1200–1300 °C. Of the interferents studied, CaCl2 and NaCl had the greatest suppressive effect on Au atomic absorption signals, at matrix concentrations between 0.1 and 0.5%m/V. In contrast, HNO3 and HCl caused no interference at levels up to 5%V/V. The best general modifiers for Au were Ni and Pd-Mo, with the latter better for wall-atomisation measurements. Although the best Au sensitivity was obtained with Pd, the short-term stability of Au solutions was poorer with this modifier than for Pd plus Mo. For platform atomisation, Ni and Pd-Mo were equally good modifiers, and interferences were less pronounced than for wall atomisation. In general, the best conditions for interference-free analysis of Au-containing samples were addition of Ni or Pd-Mo modifier, platform atomisation and peak-area measurement.