Determination of trace mercury in environmental samples by cold vapor atomic fluorescence spectrometry after cloud point extraction

A sensitive method is presented for the determination of ultra-trace levels of mercury using cold vapor atomic fluorescence spectrometry along with cloud point extraction. Preconcentration is based on the complexation of Hg(II) by dithizone, followed by micelle-mediated extraction of the complex using the surfactant Triton X-114. Foaming, which is always observed when generating vapor mercury in the presence of surfactant, was strongly reduced by using SnCl2 as a reducing reagent, and a homemade gas–liquid separator. Variables that affect the assay were optimized. These included pH value, concentration of chelating reagent, concentration of Triton X-114, equilibration temperature and time. The preconcentration of a 45-mL sample gave an enhancement factor of 29. The calibration graph is linear in the range from 0.05 to 5.0 ng mL−1 with a correlation coefficient of 0.9991. The limit of detection (3δ) obtained under the optimal conditions is 5 pg mL−1. The relative standard deviation for seven replicate determinations at 0.5 ng mL−1 level is 5.2%. The method was successfully applied to the determination of Hg in real samples.