Abstract
The improved method is developed for the usual mecury determination by cold-vapor AAS with acidic tin(II) after digestion of the sample. In the Japanese official method, iodide and its related compounds interfered with the trace mercury determination. Hence, the improvement of the official method is necessary for complicated environmental samples such as waste waters from university laboratories. The determination procedures are as follows: An aliquot (less than 100 ml) of sample solution is taken into a reaction vessel after digestion with potassium peroxodisulfate in a diluted sulfuric acid solution heated at 95 °C for 1 h. To the solution, 10 ml of 5 M sodium hydroxide, 2 ml of 1000 mg/l Cu2+ solution, 10 ml of 5% potassium zinc cyanide solution, and 2 ml of 10% tin(II) chloride solution are added, and the evolved mercury is measured with an atomic absorption spectrometer at 253.7 nm. The reducing power of tin(II) in alkaline solution is stronger than that in acidic solution because the standard redox potential for tin(II) is -0.93V vs. NHE at pH 14 (0.15V vs. NHE in acidic). However, potassium zinc cyanide is added as a masking agent for silver(I) ion because it interferes with the improved alkaline method. The detection limit and precision of the improved method are 0.5μg/l and 3%, respectively. The method was applied to the determination of mercury in waste water samples containing iodide with satisfactory results.
