SIMULTANEOUS KINETIC SPECTROPHOTOMETRIC DETERMINATION OF O-AMINOPHENOL, M-AMINOPHENOL AND P-AMINOPHENOL USING PARTIAL LEAST-SQUARES CALIBRATION

The oxidative coupling reactions of p-aminophenol with m- and p-aminop henol 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 mixt ures. The influence of Mo-V concentration, acidity, ionic strength and temperature was studied in order to establish optimum conditions, Sev eral oxidants, including Ce4+, Cr-VI, Mn-VII, H2O2 and metaperiodate a nd Fe-III, Mn-IV, Mo-V and W-V cyano complexes were tried, The Mo-V cy ano complex was chosen because it has a suitable redox potential and g ives rise to kinetically useful runs, The reaction must be implemented under sub-stoichiometric concentrations of oxidant and so the concent ration of each aminophenol in the mixture influences the reaction of t he others, originating in a system with a high degree of non-linearity , As a result, most methods of data treatment cannot be used and multi variate 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 r esults 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 1 0% in all instances, No systematic errors were detected.