Determination of Trace Mercury in Drinking Water by Hydride Generation Atomic Fluorescence Spectrometry with Ammonium Pyrrolidinedithiocarbamate Chelation and Cloud Point Extraction

Considering that the standard of HJ 694—2014 for detecting mercury in drinking water has a high detection limit and cannot meet the analysis requirements for trace mercury, the method was proposed with ammonium pyrrolidinedithiocarbamate (APDC) solution as chelating agent and non ionic surfactant Triton X-114 solution as extractant. Trace mercury in drinking water was enriched in the surfactant phase through cloud point extraction, and determined by hydride generation atomic fluorescence spectrometry. After filtration and acidification, 50 mL of the water sample was taken, and 1.5 mL of 2.0 g · L⁻¹ APDC solution and 1.5 mL of 5% (volume fraction) Triton X-114 solution were added. The mixed solution was adjusted its acidity to pH 6, equilibrated at 40 ℃ for 5 min, centrifuged at rotational speed of 2 900  r · min⁻¹ for 10 min, and cooled in the ice water bath for 5-10 min. The upper aqueous phase was discarded, and 300 μL of the defoamer prepared by mixing tributyl phosphate and ethanol at volume ratio of 1∶1 was added into the surfactant phase. The resulting solution was diluted to 5 mL by 5% (volume fraction) hydrochloric acid solution for intrumental detection. It was shown that linear relationship between values of the mass concentration and the fluorescence intensity of mercury was kept within 2.0 μg · L⁻¹, with detection limit of 0.002 μg · L⁻¹. Test for recovery was made according to the standard addition method, giving recoveries in the range of 86.8%-97.9%, and RSDs (n=6) of the determined values were not more than 8.0%. The detection limit of the method was one order of magnitude lower than that given by the standard of HJ 694—2014, which could meet the detection limit requirements for trace mercury analysis in clean water samples such as drinking water.