A Rapid Spectrophotometric Method for the Determination of Trace Level Silver Using 1, 5-diphenylthiocarbazone in Aqueous Micellar Solutions

Abstract

The very sensitive, fairly selective direct spectrophotometric method is presented for the rapid determination of silver at ultra-trace level using1, 5-diphenylthiocarbazone (dithizone) as a new micellar spectrophotometric reagent ( max= 495 nm) in a slightly acidic (0.1-1.0 M H2SO4) aqueous solution. The presence of a micellar system avoids the previous steps of solvent extraction and reduces the cost, toxicity while enhancing the sensitivity, selectivity and molar absorptivity. The  average  molar absorptive of  the Ag - dithionate complex formed in presence of  anionic  sodium deducible sulfate (SDS) surfactant was  found to be  1.6 x 105  L. mol.-1 cm-1  which was  almost  10 times higher than the value observed (1.0 x 104 L. mol.-1 cm-1) in the standard method, resulting in an increase in the sensitivity of  the method. The reaction is instantaneous and                   the absorbance remains stable for over 24 h. The Sandell’s sensitivity was found to 12 ng cm-2 of Ag. Linear calibration graphs were obtained for 0.07-10 mg L-1 of silver; the stoichiometric composition of the chelate is 1:1 (Ag: dithizone). The method is characterized by a detection limit of 0.1 µg L-1 of Ag. Large excess of over 50 cations, anions and complexing agents (e.g. EDTA, tartrate, oxalate, citrate, phosphate, azide) do not interfere in the determination. The method was successfully applied to a number of environmental water samples (potable and polluted), biological samples (human blood and urine), photographical samples and soil samples. The method has high precision and accuracy (s = ±0.01 for 0.1 mg L-1).