ADAPTIVE CALIBRATION SCHEME FOR QUANTIFICATION OF NUTRIENTS AND BY-PRODUCTS IN INSECT-CELL BIOREACTORS BY NEAR-INFRARED SPECTROSCOPY

Spectroscopic methods are gaining in popularity in biotechnology becau se of their ability to deliver rapid, noninvasive measurements of the concentrations of multiple chemical species. Such measurements are par ticularly necessary for the implementation of control schemes for cell culture bioreactors. One of the major challenges to the development o f spectroscopic methods for bioreactor monitoring is the generation of accurate and robust calibration models, particularly because of the i nherent variability of biological processes. We have evaluated several methods of building calibration models, including synthetic calibrati ons and medium spiking methods. The approach that consistently produce d reliable models incorporated samples removed from a bioreactor that were subsequently altered so as to increase the sample variation. Seve ral large volume samples were removed from a bioreactor at varying tim e points and divided into multiple aliquots to which were added random , known amounts of the analytes of interest. Near-infrared spectra of these samples were collected and used to build calibration models. Suc h models were used to quantify analyte concentrations from independent samples removed from a second bioreactor. Prediction errors for alani ne, glucose, glutamine, and leucine were 1.4, 1.0, 1.1, and 0.31 mM, r espectively. This adaptive calibration method produces models with les s error and less bias than observed with other calibration methods. So mewhat more accurate measurements could be attained with calibrations consisting of a combination of synthetic samples and spiked medium sam ples, but with an increase in calibration development time.