Abstract
The degree of interference from various sulphates in the determination of lead by flameless a.a.s. is high (e.g. the decrease in the signal from lead is 10% for 2 nanomol of sodium sulphate) and decreases in the order sodium ⩾ potassium ⩾ calcium ⩾ magnesium. The interference from magnesium sulphate can be eliminated by ashing the sample at 870 ± 10°C. Results obtained from high-temperature equilibrium calculations show that gaseous lead sulphide is responsible for the interferences in the presence of sodium sulphate. Theoretical conditions for the formation of gaseous lead sulphide are outlined. The influence of carbon on the reactions involved was investigated by use of standard graphite as well as glassy carbon tubes; the results are compared with those found theoretically. In the presence of a tenfold excess of lanthanum(III), the recovery of lead is higher than 90% for all the sulphates investigated, at least up to an amount of 0.2 μ mol. The addition of oxygen as well as hydrogen to the inert gas decreases the interference from sodium sulphate, in accordance with the theoretical predictions.
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