A simple, rapid and sensitive spectrophotometric method for the determination of trace amounts of 4-aminoantipyrine in aqueous solution is described. The method is based on a coupling reaction between 4-aminoantipyrine and diazotised 4-nitroaniline to form an intense yellow, water-soluble dye that is stable and has a maximum absorption at 380 nm. A graph of absorbance versusconcentration shows that Beer's law is obeyed over the concentration range 25-750 pg of 4-aminoantipyrine in a final volume of 25 ml (is., 1-30 p.p.m.) with a molar absorptivity of 1.3 x 104 I mol-1 cm-1, a Sandell sensitivity of 156.4 x 10-4 pg cm-2, a relative error of -0.8 to +I .5% and a relative standard deviation of 0.3-2.0% depending on the concentration.The optimum conditions for full colour development and the interference of foreign organic compounds have been investigated. The proposed method does not require either temperature control or a solvent extraction step.

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