Evaluation of data produced by optode arrays under flow injection analysis(FIA) conditions using a partial least squares method (PLS2)

Transient diffuse reflectance spectra in the visible wavelength region from an enzyme optode were evaluated to determine artificial mixtures consistin g of penicillin and ampicillin simultaneously. In order to achieve a discri mination of the samples the optode operated at two different working pH val ues. Using an appropriate FIA modus a linear range in the increase and decr ease of the time-dependent signal was registered which could be easily fitt ed by means of ordinary linear regression. In this way characteristic stati c and dynamic features of the enzyme catalyzed reaction could be extracted for the evaluation by partial least-squares (PLS). The pre-processed raw da ta were differently weighted and the optimal number of primary factors was each selected by full cross validation. The interpretation of the spectral loadings and the correlation matrix identifies redundant variables resultin g in a model with an optimal number of variables. The results obtained with this model show that the straightforward linear regression can be a suffic ient approach to avoid the introduction of systematic errors in on-line pre -processing of data. (C) 1999 Elsevier Science BN. All rights reserved.