Determination of Trace Mercury in Geochemical Samples by Cold Atomic Mercury Generation-Atomic Fluorescence Spectrometry

The sample (0.200 0 g) was added into 5 mL of a mixture of hydrochloric acid and nitric acid (9+1), and the solution was heated in boiling water for 2 h. After cooling, 5 mL of a solution containing 75 g·L^-1 thiourea and 75 g·L^-1 ascorbic acid was added and mixed well. Then the volume of the solution was made up to 25 mL with 3 mol·L^-1 hydrochloric acid solution containing 5 g·L^-1 tartrate. After shaking, the sample solution was used for cold atomic mercury generation-atomic fluorescence spectrometry analysis. Working conditions of the instrument were chosen as follows: 1 negative high voltage of photomultiplier tube was 230 V; 2 peak currents of main cathode and auxiliary cathode were 25 mA, 0, respectively; 3 a mixed solution containing 2 g·L^-1 KOH and 0.05 g·L^-1 KBH₄ was used as reducing agent; 4 flow-rate of carrier gas (argon) was 800 mL·min^-1; 5 temperature of atomizer was 200 ℃; 6 height of atomizer was 7 mm. It was showed that, linear relationship was found between fluorescence intensity and mass of mercury within 12.00 ng, with detection limit (3s) of 0.24 ng·g^-1. The proposed method was applied to determination of mercury in GBWs for geochemistry, giving results in consistency with certified values and RSDs (n=12) less than 8.0%.