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

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.