Diazotised 4-nitroaniline as a chromogenic reagent for the determination of trace amounts of pyrrole in aqueous solution

Abstract

A sensitive spectrophotometric method for the determination of trace amounts of pyrrole in aqueous solution is described. The method is based on the reaction of pyrrole with diazotised 4-nitroaniline to produce, in the presence of sodium acetate, an intense yellow, water-soluble, stable monoazo dye, which shows maximum absorption at 420 nm. A graph of absorbance versus concentration indicates that Beer's law is obeyed over the concentration range 5–100 µg of pyrrole in a final volume of 25 ml, i.e., 0.2–4 p.p.m., with a molar absorptivity of 2.32 × 10⁴ l mol^–1 cm^–1, a Sandell sensitivity of 0.0029 µg cm^–2, a relative error of +0.9 to –1.7% and a relative standard deviation of 0.6–2.0%, depending on the concentration. A study has been made to determine the optimum conditions of the colour reaction. Interferences from foreign organic compounds have been examined and the structure of the monoazo dye is suggested.