Solid-Phase Extraction and Spectrophotometric Determination of Trace Amounts of Mercury in Natural Samples

Abstract.

A sensitive and selective solid phase spectrophotometric method for the determination of trace amounts of inorganic mercury is described. Hg²⁺ was sorbed on a silica gel-packed column as an Hg²⁺–N,N′-bis(2-mercaptophenyl)ethanediamide (H₂L) complex. The Hg²⁺ complex was eluted from the column using 7 mL of acetone. Various parameters including pH, column flow rate, and ligand concentration were optimized. The complex was found to obey Beer’s law from 2.3 to 73.7 µg mL⁻¹ within the optimum range when the preconcentration factor was two. The effective molar absorption coefficient at 523 nm was 1.17×10³ L mol⁻¹ cm⁻¹ at 523 nm. The concentration limits in Beer’s law dropped from 0.09 to 2.95 µg mL⁻¹ within the optimum range when the preconcentration factor was 50. The relative standard deviation at a concentration level of 5 µg mL⁻¹ Hg²⁺ (9 repetitive determinations) was 1.6%. The detection limits are 0.34 µg mL⁻¹ and 0.015 µg mL⁻¹ when the preconcentration factors are 2 and 50, respectively. The method has been used for routine determination of trace levels of Hg²⁺ in natural waters. The potential application of this method for the removal of Hg²⁺ from natural samples (sea water and lake water) spiked with 100 ng mL⁻¹ of Hg²⁺ was studied. In order to validate the proposed method, LGC 6156 (harbour sediment – extractable metals) was analysed by this method. The results proved that excellent extraction of Hg²⁺ from both natural water samples was obtained by solid phase extraction using N,N′-bis(2-mercaptophenyl) ethanediamide.