Fluorimetric determination of arsenite and arsenate in water using fluorescein and iodine
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A rapid, simple and sensitive fluorimetric method has been developed for the determination of inorganic arsenic. The method is based on the competitive reaction of arsenite and 2',7'-dichlorofluoresecin (DCF) as fluoregenic reagent (lambda(ex) = 510 nm, lambda(em) = 528 nm) at pH 6.5-7.5 with iodine (I-2) to cause the increasing fluorescence intensity of the solution. Arsenate and other ions do not react with iodine. After reduction to the trivalent state by using L-cysteine, total arsenic is determined by spectrofluorimetry. Arsenate concentration can be calculated by difference. The calibration graph is linear over the range 4-180 ng/mL arsenite. The linear regression equation is DeltaF = 7.82C + 0.76 and the relative coefficient is 0.9991. The detection limit is 0.6 ng/mL arsenite. The recovery of this method for detecting arsenite is 96-105%. The method has been applied successfully to the determination of arsenite in tap and pool water.