4-(4-Diethylaminophenylazo)-1-(4-nitrobenzyl)pyridinium bromide is a very stable compound that can be used in the determination of anionic surfactants[1][2].
References
[1] Higuchi K, et al. Spectrophotometric determination of anionic surfactants in river waters using 1-(4-nitrobenzyl)-4-(4-diethylaminophenylazo)-pyridinium bromide. Analyst, 1980, 105(1253): 768-773. [2] Motomizu S, et al. Solvent extraction-spectrophotometric determination of anionic surfactants with ethyl violet. Analytical Chemistry, 1982, 54(3): 392-397.
