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 reaction products (i.e. these absorption curves are seriously overlapped with each other), therefore the simultaneous determinations of them are carried out by using neither differential rate kinetic method nor multi-wavelength spectrophotometry and nor derivative spectrometry unless preseparation tactics of them are taken. In this paper, the conditions for chromogenic reactions of leucine, isoleucine, tryptophan, lysine, threonine, valine, phenylalanine 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 essential 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 experiments show that the PLS method is better than Kalman filter method.