A Simple Spectrophotometric Determination of Trace Level Mercury Using 1,5-Diphenylthiocarbazone Solubilized in Micelle

A very simple, ultra-sensitive and fairly selective non-extractive spectrophotmetric method is presented for the rapid determination of mercury(II) at ultra-trace level using 1,5-diphenylthiocarbazone (dithizone) as a new micellar spectrophotometric reagent (λmax = 490 nm) in a slightly acidic (0.07 - 0.17 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 the molar absorptivity. The reaction is instantaneous and the absorbance remains stable for over 24 h. The average molar absorption coefficient and Sandell’s sensitivity were found to be 5.02 × 104 L mol-1 cm-1 and 10 ng cm-2 of Hg, respectively. Linear calibration graphs were obtained for 0.05 - 10 mg L-1 of Hg; the stoichiometric composition of the chelate is 1:2 (Hg:dithizone). The method is characterized by a detection limit of 1 µg L-1 of Hg. Large excesses of over 60 cations, anions and complexing agents (e.g. EDTA, tartrate, oxalate, citrate, phosphate, thiourea, azide, SCN-) 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; milk and fish) and soils; solutions contained both mercury(I) and mercury(II) as well as complex synthetic mixtures. The method has high precision and accuracy (s = ±0.01 for 0.1 mg L-1).