Determination of eight essential amino acids in mixtures by chemometrics-spectrophotometry without separation

There are almost no differences among the reaction rates of eight essential amino acids with ninhydrin and among the absorption spectra of their react ion products (i.e. these absorption curves are seriously overlapped with ea ch other), therefore the simultaneous determinations of them are carried ou t by using neither differential rate kinetic method nor multi-wavelength sp ectrophotometry and nor derivative spectrometry unless pre-separation tacti cs of them are taken. In this paper, the conditions for chromogenic reactio ns of leucine, isoleucine, tryptophan, lysine, threonine, valine, phenylala nine and methionine with ninhydrin have been anew optimized, then a partial least-squares (PLS) method for simultaneous determination of two mixtures each of which contains five different amino acids among above eight essenti al amino acids (processing data with microcomputer) has been developed. The method is simple, rapid, accurate and the results agree with both present values and those obtained by amino acid autoanalyzer. Besides, our experime nts show that the PLS method is better than Kalman filter method. (C) 2001 Elsevier Science B.V. All rights reserved.