INDIVIDUAL KINETIC DETERMINATIONS USING PARTIAL LEAST-SQUARES CALIBRATION

The slow oxidation reactions of cysteine, tyrosine and tryptophan by h exacyanomanganate(IV) were used to investigate partial least squares c alibration (PLS) as a method to be applied to the kinetic determinatio n of individual species, All the three reactions are first order in he xacyanomanganate(IV) concentration and the reactions with cysteine and tyrosine are first order in amino acid concentration. The stoichiomet ry was studied in each case, The determination results were always com pared with those obtained by applying the initial rate method to the s ame kinetic runs, When suitable kinetic curves are obtained and the in itial rate is easily determined, both methods give similar results; ho wever, when the initial rate is not easily determined (too fast reacti on, slope that changes very quickly, etc.) the results obtained with P LS are better (better precision and wider dynamic range), Moreover, an d in contrast to the initial rate method, PLS allowed tryptophan to be determined in the presence of some different feed matrices, provided the calibration set was of the same nature as the samples. This advant age is of general application and makes the analytical method more rob ust, PLS was tested on uncatalysed reactions but it could equally be a pplied to catalysed reactions.