Automatic determination of mercury in samples of environmental interest.

Abstract

An automaticflow injection (FI) system for the determination of mercury was developed using a commercial cold vapour atomic absorption spectrophotometer (CVAAS). Control and data acquisition in the FI system was done with an IBM-PC 286 XT compatible microcomputer and a home-made interface, using software written in Q,uickBasic 4"5. Mercury content was determined by: sampling using a combination offour electromechanical three-way poly(tetrafluoroethylene) valves; separation of the dissolved reduced mercury in a gas]liquid separation cell using nitrogen as carrier, followed by amalgamation of the stripped metal on a gold wire column; after stripping the metal, cleaning the separation cell using vacuum, which was controlled by a three-way electromechanical valve; heating the gold wire column automatically to release the amalgamated mercury using an external nichrome wire coil; storing the output signals automatically to calculate the final mercury concentration, using commerdally available software. The optimized system presents a detection limit of 5"3 ng of mercury (30 pg absolute) using 5"7 ml (three injections of 1900 Izl of the sample) with an analytical frequency of six samples per hour and reproducibility of5%. The procedure was used to determine mercury infish, ha# and natural water samples. [7, 8]. Since then, numerous modifications and adaptations have been reported in the literature [7, 9-21]. These modifications include adaptation of the cold vapour to a flow injection (FI) system [11, 16-18], the use of chromatography columns for speciation [19], utilization of gold filled columns for one or two stage mercury amalgamation [10, 13, 14, 20] and, finally, by automation of the analyser itself [9, 21 ].