A simple, sensitive and highly selective direct spectrophotometric method for the determination of trace levels of mercury(II) in various samples is described. Diphenylthiocarbazone (dithizone) reacts in slightly acidic 50% aqueous 1,4‐dioxane media (0.18–1.80 M sulphuric acid) with mercury(II) to give an orange chelate which has an absorption maximum at 488 nm. The average molar absorption co‐efficient and Sandell′s sensitivity were found to be 2.5×10⁴l mol⁻¹ cm⁻¹ and 0.015 μg of Hg(II) cm⁻², respectively. The reaction is immediate and absorbance remains stable for over 24 h. Beer′s law is obeyed for concentration range of mercury(II) between 0.1 μg ml⁻¹ and 25 μg ml⁻¹; the stoichiometric composition of the chelate is 1 :2 (mercury : dithizone). The various analytical parameters, such as effect of time, acidity, reagent concentration and foreign species, were studied. The method was applied successfully to a number of environmental waters (portable and polluted), biological samples (human blood, urine and fish), soils, plant samples (potato, cabbage, lettuce, carrot and tomato), solutions containing both mercury(I) and mercury(II) and complex synthetic mixtures. The method is very simple and requires no solvent extraction or pre‐concentration steps.

A very simple, ultra‐sensitive and fairly selective new spectrophotometric method has been developed for the rapid determination of lead(II) at ultra‐trace level using 1,5‐diphenylthiocarbazone (dithizone) in presence of aqueous micellar solutions. The proposed method enabled the determination of lead down to µg l⁻¹ in human blood and urine in aqueous media without resource of any “clean‐up” step. The most remarkable point of this method is that the presence of micellar system avoids the previous steps of solvent extraction and reduces the cost, toxicity while enhancing the sensitivity, selectivity and the molar absorptivity. The complex formation of lead in blood with dithizone was completed within a minute at room temperature and the absorbance remains stable for 24 h. The average molar absorption coefficient and Sandell′s sensitivity were found to be 3.99×10⁵ l mol⁻¹ cm⁻¹ and 30 ng cm⁻² of Pb, respectively. Linear calibration graphs were obtained for 0.06–60 mg l⁻¹ of Pb^II; the stoichiometric composition of the chelate is 1:2 (Pb:dithizone). The interference from over 60 cations, anions and complexing agents has been studied at 1 mg l⁻¹ of Pb^II. The method was successfully used in the determination of lead in several biological samples (human blood and urine and bovine liver), solution containing both lead(II) and lead(IV) and complex synthetic mixtures. The results of biological analyses by the spectrophotometric method were in excellent agreement with those obtained by AAS. The results of lead concentration in biological samples were varied with age, sex and place which have been discussed.