Determination of arsenic in environmental and biological samples using toluidine blue or safranine O by simple spectrophotometric method.

A simple spectrophotometric method has been developed for the determination of arsenic in various environmental and biological samples. The method is based on the reaction of arsenic(III) with potassium iodate in acid medium to liberate iodine. This liberated iodine bleaches the blue color of toluidine blue or pinkish red color of safranine O. The decrease in absorbance at 628 or 532 nm is directly proportional to arsenic(III) concentration and obeys Beer's law in the range of 1.2-10.5 or 0.4-11.5 microg mL(-1) for arsenic(III). The molar absorptivity, Sandell's sensitivity, detection limit and quantitation limit of the method using toluidine blue or safranine O were found to be 1.076 x 10(4) or 1.388 x 10(4) L mol(-1) cm(-1), 9.66 x 10(-3) or 7.49 x 10(-3) microg cm(-2), 0.308 or 0.250 microg mL(-1), 0.934 or 0.759 microg mL(-1) respectively. The relative standard deviation for five replicate analyses of 4 microg mL(-1) of As(III) using toluidine blue or safranine O were 0.60% or 0.80%. The optimum reaction conditions and other analytical conditions were evaluated. The effect of interfering ions on the determination is described. The proposed method is free from any interference. The method has been used for the determination of arsenic in various environmental and biological samples.