Atomic absorption determination of total mercury by a combined iron(III)-sodium borohydride reduction reagent

Abstract

Organic mercury compounds such as methylmercury (II) chloride (MMC) and phenylmercury(II) acetate (PMA) were decomposed and reduced by a combined Fe(II)-or Fe(III)-NaBH₄ reagent. A new method utilizing this phenomenon for the determination of mercury in solution by a cold vapor atomic absorption technique is described. A closed type cell (light path length: 10 cm) equipped with a reaction vessel was used for a device. The procedure is as follows. 150 ml of sample solution containing (0.151.05)μg as mercury was taken into a reaction vessel. After the vessel was connected with the closed type cell, 1.5 ml of Fe(II) or Fe(III) (1.00×10³ ppm) and 1 ml of NaBH₄ {1% (w/v)} solutions were added to the vessel through an upward inlet of the cell, and then the inlet was closed immediately with a stopcock. Then the absorbance due to vaporized mercury atoms was measured until the highest absorption peak was obtained. The addition of Fe(III) was more effective for the determination of organic mercury than that of Fe(II). The linear standard curves for MMC and PMA (as well as HgCl₂) were obtained by the method using a combined Fe(III)-NaBH₄ reagent. The detection limit (S/N=2) for mercury was down to 0.1 ng/ml.
The application of this method is expected for the determination of total mercury and for the selective determination of inorganic and organic mercury in natural water samples.