USE OF PH GRADIENTS IN CONTINUOUS-FLOW SYSTEMS AND MULTIVARIATE REGRESSION TECHNIQUES APPLIED TO THE DETERMINATION OF METHIONINE AND CYSTEINE IN PHARMACEUTICALS
F. Blasco et al., USE OF PH GRADIENTS IN CONTINUOUS-FLOW SYSTEMS AND MULTIVARIATE REGRESSION TECHNIQUES APPLIED TO THE DETERMINATION OF METHIONINE AND CYSTEINE IN PHARMACEUTICALS, Analytica chimica acta, 348(1-3), 1997, pp. 151-159
The simultaneous spectrophotometric determination of methionine and cy
steine in presence of cystine and other compounds in pharmaceuticals,
using a multivariate calibration method, was studied. The method is ba
sed on the reaction between the analytes and the o-phthalaldehyde-N-ac
etyl-L-cysteine (OPA-NAC) reagent performed in a continuous-flow syste
m (FI). The FI system allows the generation of a local pH gradient in
order to produce spectral and/or kinetic changes in the W-Vis spectra
of the amino acid-OPA-NAC derivatives. This information is used to imp
rove the prediction ability of the Partial Least-Squares (PLS) models.
The performance of two FI assemblies, the selection of variables and
the pretreatment of the data were studied. A series of eighteen synthe
tic solutions containing different concentrations of methionine, cyste
ine and cystine was prepared and used as a calibration set to study th
e PLS models. In addition, solutions of a commercial formulation conta
ining the three amino acids were prepared and the content of methionin
e and cysteine was predicted. The results obtained using the PLS model
s were compared with those obtained using an HPLC method.