Comparison of chemical modifiers for the determination of gold in biological fluids by electrothermal atomic absorption spectrometry
The use of various isomorphous metals as chemical modifiers on the determination of gold has been investigated. The temperature programmes and the masses of modifiers were carefully optimized. Noble metals, copper, nickel, and rhenium increased the atomic absorption signal of gold and raised the maximum pyrolysis temperature from 700 to 1000 °C. In the presence of 20 µg of ascorbic acid this temperature was 1000 °C, whereas in combination with 1 µg of Pd it increased to 1150 °C. On the basis of platform atomization and integrated absorbance measurements, the best sensitivity for aqueous solutions was obtained with the mixed modifiers rhodium–rhenium (m0= 7.3 pg), ascorbic acid–palladium (m0= 7.1 pg) or ascorbic acid–rhodium (m0= 6.8 pg), whereas the characteristic mass in the absence of modifiers was 12.2 pg. The limit of detection was 0.23 µg l–1 in the absence of modifier, whereas it was 0.12 µg l–1 in the presence of the mixed modifier rhodium–rhenium. In the absence of chemical modifiers, a fractional order of release was observed for gold, whereas in the presence of modifiers an approximately first-order release was observed. The determination of gold in biological fluids was interference-free and complete recovery was obtained when stabilized temperature platform furnace conditions were fulfilled. Constant signals, without double peaks and shoulders, were obtained only in the presence of modifiers. It was found that gold solutions stored in the autosampler cups during measurements of the samples were stable only in the presence of 0.5 g l–1 NH4SCN or 1.0 g l–1 ascorbic acid.