Kinetic spectrophotometric determination of trace cadmium and lead based on its inhibitory effect on discoloring reaction of arsenazo I and peroxide hydrogen

A kinetic spectrophotometric method for the simultaneous determination of trace cadmium and lead has been developed,based on inhibitiv e effect of lead and cadmium on the discoloring reaction of Arsenazo Ⅰ by peroxide hydrogen in ammonia solution medium.The linear range of determination is 0.005-0.50 μg/mL for lead and 0.002-0.80 μg /mL for cadmium.Foreign ions hardly interfere in the determination.The interferences from Mg2+,Ca2+,Zn2+,Sn2+ ions were eliminated by extraction and reextraction with dithizone.The method has been applied to the simultaneous determination of lead and cadmium in samples with the relative standard deviations(RSDs) of less than 3.0% for lead and 2.6% for cadmium,and the recovery of 98%-101% for lead and 96%-97% for cadmium.