Second order multivariate curve resolution applied to the flow injection analysis of mixtures of amino acids

A flow injection system with diode-array multi-wavelength spectrophotometric detection was used to generate second order data. The system was applied to monitoring the reaction between amino acids (lysine and proline) and l,2-naphthoquinone-4-sulfonate (NQS) to give the corresponding derivatives. The sample injection produced a pH gradient which allowed the discrimination of the time profiles of the different amino acid derivatives. Each amino acid gave a FIA response which was arranged in a data matrix whose chemical rank was higher than one (more than one spectrophotometrically active species was present in the reaction system). The method was applied to the simultaneous determination of Lys and Pro by second order multivariate curve resolution, obtaining a global quantification error of 0.36%. The analysis of one of these amino acids in presence of the other as interference by using a pure standard (without any information about the interference) was also studied. In this case, errors in the quantification were of 2.75 and 3.0% for Lys and Pro, respectively.