A new catalytic spectrophotometric method for determing trace arsenium has been proposed.The method is based on the catalytic effect of As(V) in discoloring reaction between KIO 3 and Thymol Blue in HCl medium (pH=0.8) and the presence of activator citric acid.The method has good selectivity and the linear range is 0.00～10.00μg/L,detection limit is 6.3×10 -11 g/ml.The method has been used for the determination of trace arsenium in celery,human hair and waste water samples,and RSD is 2.1%～3.2% and recovery is 97%～102%.
