Simultaneous kinetic spectrophotometric determination of o-, m-and p-aminophenol using partial least squares calibration

Abstract

The oxidative coupling reactions of p-aminophenol with m-and p-aminophenol in the presence of octacyanomolybdate(v) were used as the basis of a differential kinetic method for the simultaneous determination of o-, m-and p-aminophenol (o-, m-and p-AP) in binary and ternary mixtures. The influence of Mo^v concentration, acidity, ionic strength and temperature was studied in order to establish optimum conditions. Several oxidants, including Ce⁴⁺, Cr^VI, Mn^VII, H₂O₂ and metaperiodate and Fe^III, Mn^IV, Mo^V and W^V cyano complexes were tried. The Mo^V cyano complex was chosen because it has a suitable redox potential and gives rise to kinetically useful runs. The reaction must be implemented under sub-stoichiometric concentrations of oxidant and so the concentration of each aminophenol in the mixture influences the reaction of the others, originating in a system with a high degree of non-linearity. As a result, most methods of data treatment cannot be used and multivariate calibration (PLS) was applied to the data acquired by a diode-array spectrophotometer between 340 and 500 nm. PLS calibration with a number of factors ranging between six and nine allowed satisfactory results for all kinds of mixtures. Aminophenols can be determined over the concentration range 0.1–1.0 mmol l^–1 for o-AP, 0.3–1.0 mmol l^–1 for m-AP and 0.25–3.0 mmol l^–1 for p-AP with errors of less than 10% in all instances. No systematic errors were detected.