Synthesis and analytical applications of 4-aminopyrazolone derivatives as chromogenic agents for the spectrophotometric determination of phenols

The synthesis of simple, extensively conjugated chromophores as substitutes for 4-aminoantipyrine (4-AAP) capable of causing hyperchromic shifts when coupled with phenols is described. The 4-aminopyrazolone derivatives synthesised are subsequently applied for the spectrophotometric assay of phenolic compounds and the advantages of each of the proposed systems are highlighted. No improvement is made on the detection of para-substituted phenols as well as polychlorophenols (e.g. pentachlorophenol). An increase in the sensitivity of coupling products is obtained for certain phenolic compounds as indicated from the comparison of the individual responses. The proposed methods have analogous analytical features and in some cases show considerable improvements compared to the 4-AAP method. Beer's law is obeyed over a wide dynamic range (up to ca. 500 mu g/l) and the relative standard deviations are <3.4%. The methods are applied satisfactorily for phenol assay in real samples, however, taking into account the intrinsic differences of the methods in the responses to the various phenolic compounds. (C) 2000 Elsevier Science B.V. All rights reserved.