ONLINE PRECONCENTRATION OF INORGANIC MERCURY AND METHYLMERCURY IN SEA-WATER BY SORBENT EXTRACTION AND TOTAL MERCURY DETERMINATION BY COLD VAPOR ATOMIC-ABSORPTION SPECTROMETRY

A comparative study of three mercury chelate forming reagents [diethyl dithiocarbamate, pyrrolidin-1-yldithioformate and diphenylthiocarbazon e (dithizone)] has been carried out for the preconcentration of ultrat race amounts of inorganic mercury and methylmercury in silica C-18 min icolumns as the solid sorbent. Sample flow injection in-line sorbent e xtraction was coupled with continuous cold vapour atomic absorption sp ectrometry (CVAAS) for detection. Results showed the superiority of th e carbamate type reagents over the dithizone for the on-line formation and preconcentration of the corresponding mercury chelates. Using die thyldithiocarbamate (DDC) as reagent, aqueous sample volumes of 100 ml can be preconcentrated with 100% efficiency for both inorganic mercur y and methylmercury. Quantitative release of the retained DDC chelates was obtained for volumes of eluent (ethanol) of 50 mu l. Following th e proposed procedure, detection limits of 16 ng/l. of mercury were ach ieved for sample volumes of 25 ml. The relative standard deviation was +/-3.4% at 0.5% mu g/l. Hg(II) levels. The method has been successful ly applied to the determination of low levels of mercury in sea-water.