Spectrophotometric Determination of Trace Mercury in Aqueous Solution with Thiocyanate-Acridine Red

A highly sensitive spectrophotometric method for determination of mercury has been developed, based on mercury in an excess of thiocyanate to form Hg(SCN) 2- 4, then formation of the 1∶2 ion association complex of Hg(SCN) 2- 4 with acridine red in the presence of polyvinyl alcohol gum Arabic. The molar absorptivity is 3.1×10 5 L·mol -1 ·cm -1 . The maximum absorbance of ion association against the reagent blank is at 583 nm. Beer's law is obeyed in the range of 0～9 μg Hg(Ⅱ)/25 mL. The relative standard deviation for the determination of 4.0 μg Hg(Ⅱ)/25 mL is 2.1%( n =9), and the detection limit is 0.35 μg Hg(Ⅱ)/(3 σ,n =11). The procedure is relatively simple. Elimination of liminated the interference is achieved by adding the mixed masking agents of potassium fluoride sulphosalicylic acid citric acid into sample solution, so the determination has very good selectivity. Trace mercury in aqueous solution has been satisfactorily determined directly by the method.