Novel colorimetric assay of indomethacin using 4-carboxyl-2,6-dinitrobenzene diazonium ion.

A simple, sensitive and direct colorimetric method for the determination of indomethacin either in pure form or in capsules has been developed. The method is based on the diazo coupling reaction between indomethacin and a highly reactive arenediazonium ion, 4-carboxyl-2,6-dinitrobenzene diazonium ion, with the consequent formation of an azo dye. The reaction is fast and gave an orange azo dye in ethyl acetate.