SPECIATION AND DETERMINATION OF CHROMIUM IN WATERS

Chromium is a metal which has both biological and environmental interest. It occurs in nature mostly in two stable oxidation states Cr(III) and Cr(VI). Cr(III) is non-toxic and plays a significant role in carbohydrate and fat metabolism, whereas Cr(VI) is highly toxic (MAC value 50 mug L-1 only). Being a major industrial pollutant, it has a hazardous effect on man, animal and plant life. In the present investigation, an attempt has been made to develop a highly selective and sensitive method for the spectrophotometric determination of Cr(III), Cr(VI) and total Cr in various water samples. Cr(VI) is extracted with N-hydroxy-N, N'-diphenylbenzamidine in chloroform over 0.2-0.8 M HCl and for total Cr the sample is oxidised before extraction. The extracts are separately reacted with 1,5-diphenylcarbazide in strong hydrochloric acid media to give a red-violet coloured compound having a molar absorptivity of (9.10) X 10(4) L mol-1cm-1 at lambda(max) 540 nm. The difference between the two gives the value for Cr(III) present in water sample. Various analytical parameters such as solvent effect for extraction of the metal, temperature effect, salt effect, effect of reagent concentration and diverse ions have been studied. The method follows Beer's law up to 0.43 mug L-1 of chromium with a correlation coefficient value of 0.99. The relative standard deviation of the method for 1 0 replicate measurement is +/- 2.0%. The detection limit of the method is 3 mug L-1. The system has been successfully applied for the determination of chromium in effluents of various industries.