Diazotised sulphanilic acid as a spectrophotometric reagent for the determination of trace amounts of indole in aqueous solution

Abstract

A spectrophotometric method for the determination of trace amounts of indole in aqueous solution is described. The method is based on the coupling reaction of the determinand with diazotised sulphanilic acid to form, in an acidic medium, an intense yellow, water-soluble, stable azo dye, which shows maximum absorption at 445 nm. The graph of absorbance versus concentration in linear, indicating that Beer's law is obeyed over the range 30–90 µg of indole in a final volume of 25 ml, i.e., 1.2–3.6 p.p.m., with a molar absorptivity of 33.4 × 103 l mol–1 cm–1, a sensitivity index of 0.0035 µg cm–2, a relative error of 0 to –1.6% and a relative standard deviation of 0.2–1.9%, depending on the determinand concentration. The optimum reaction conditions and interferences from foreign organic compounds have been investigated.