XYLENOL ORANGE AS A NEW REAGENT FOR THE COLORIMETRIC DETERMINATION OFSELENIUM AND TELLURIUM

Xylenol orange is proposed as new sensitive reagent for the colorimetr ic determination of selenium and tellurium. The reagent forms a pink c olored radical cation with selenite and tellurite instantaneously at r oom temperature in slightly acidic medium. The pink species exhibits a n absorption maximum at 568 and 569 nm with a molar absorption coeffic ient of 2.69 x 10(4) and 2.82 x 10(4) 1 mol(-1) cm(-1) and Sandell sen sitivity of 2.94 and 4.52 ng cm(-2) for selenite and tellurite, respec tively. A 10-fold molar excess of the reagent is necessary for the dev elopment of the maximum color intensity. Beer's law is obeyed over the concentration range 0.10-5.50 and 0.13-6.38 mu g ml(-1) of selenium a nd tellurium, respectively with an optimum concentration range of 0.35 -5.10 and 0.40-6.00 mu g ml(-1), respectively using Ringbom method. Th e effects of acidity, time, temperature, order of addition of reagent, reagent concentration and the tolerance limit of the method towards v arious cations and anions usually associated with. selenium and tellur ium are reported. The proposed method is extremely sensitive, reproduc ible and has been satisfactorily applied to the determination of trace amount of selenium in polluted water, plant material and medicated sh ampoo.