The determination of mercury and its organo compounds by high performance liquid chromatography-atomic flourescence spectrometry.

A number of digestion procedures used for the preparation of soil and sediments samples for the determination of total mercury by cold vapour atomic fluorescence spectrometry were investigated. Satisfactory results were obtained from a closed microwave digestion procedure for which 0.5g of soil or sediment sample was taken and heated with 3 mL of nitric acid and 1 ml of hydrogen peroxide. After cooling down of the digest, 0.5 mL of potassium permanganate solution (60 g.L[-1]) was added and left to react for 30 min to 4 hours following the decomposition of the sample. The excess of potassium permanganate was then reduced with 0.5 mL of hydroxyammonium chloride (20 g.L[-1]). After optimisation, this procedure was applied to the analysis of 50 sediment samples.The accuracy of this method was confirmed by recoveries of total mercury in certified reference material (C74-05) containing 294 ng.g[-1] mercury and mean recoveries of 101.6 +/- 4.4 % were obtained.The second part of this work covered the speciation of organo mercury compounds in sediments by high performance liquid chromatography - atomic fluorescence spectrometry. Methyl mercury and mercury in standard solutions were successfully separated using a Cig loaded silica column. The resolution obtained using a Hypersil column (medium carbon load) was 67. Levels of methyl mercury as low as 2 ng.g[-1] were detected in aqueous solutions. Two types of extraction procedures were investigated for the determination of organo mercury compounds by HPLC-AFS. Acid leaching extraction procedure was the most promising of the two methods. For this procedure, 1 g of sample was taken and 10 mL of 6M HC1 was added, the sample was shaken for at least 15 min before being centrifuged. 5 mL of aliquot was treated and diluted in order to obtain a pH greater than 4. This procedure although allowing qualitative analysis did not allow quantitative determination of mercury and methyl mercury.