COMPARISON OF MODIFIERS FOR MERCURY SPECIATION IN WATER BY SOLID PHASE EXTRACTION AND HIGH PERFORMANCE LIQUID CHROMATOGRAPHY-ATOMIC FLUORESCENCE SPECTROMETRY

Diethyldithiocarbamate and 2-mercaptoethanol modifiers were compared for the preconcentration of mercury species in water by C-18 solid phase extraction (SPE). The recovery values of mercury species were determined by high performance liquid chromatography-atomic fluorescence spectrometry. The eluent type, pH, chloride ion concentration, humic acid concentration, and storage time were evaluated to compare the preconcentration efficiency. L-cysteine was employed to elute the mercury compounds. Less eluent was needed for 2-mercaptoethanol modified SPE than for diethyldithiocarbamate modified SPE at an L-cysteine concentration of 0.12%. Diethyldithiocarbamate modified SPE could be used over a wider pH range and higher humic acid concentrations, whereas 2-mercaptoethanol modified SPE was less affected by the chloride concentration. Both modified SPE systems stored mercury species for 5 days, but diethyldithiocarbamate modified SPE could be stored longer. Diethyldithiocarbamate SPE provided limits of detections of 3.5, 2.5, and 4 ng.L-1 and average recoveries of 90.78 +/- 3.37%, 96.79 +/- 5.12%, and 84.88 +/- 5.37% for mercury(II), methylmercury, and ethylmercury, respectively. The relative standard deviation was less 6.5%. For 2-mercaptoethanol modified SPE, the limits of detection were 1.4, 1, and 1.6 ng.L-1 and the recoveries were of 87.66 +/- 8.45%, 86.70 +/- 2.61%, and 91.31 +/- 6.98% for mercury(II), methylmercury, and ethylmercury, respectively, with a relative standard deviation below 9.7%. Water should be characterized for its physical and chemical characteristics before mercury preconcentration to choose the most suitable method