ESTIMATION OF SOLVENT-MODULATED LINEAR ADSORPTION PARAMETERS OF TAXANES FROM DILUTE PLANT-TISSUE CULTURE BROTH

A stepwise elution technique is developed to estimate the linear solve nt-modulated isotherm parameters of taxanes from dilute plant tissue c ulture broth. The technique is proven to be robust under various exper imental conditions because mass transfer effects are decoupled from is otherm effects on elution bands. Simple algebraic equations are derive d to relate isotherm parameters to the retention times at different so lvent compositions in stepwise elution under volume overload condition s. A minimum loading volume, which is a function of mass transfer para meters, column geometries, and adsorption affinities, is estimated fro m moment analysis to ensure that band spreading due to mass transfer d oes not affect the accuracy of this method. The isotherms of a low-cos t solute, phenylalanine, under different ethanol concentrations are me asured by a standard multiple frontal chromatography method. The resul ts serve as benchmarks for the parameters that are estimated over the same ethanol concentration range using the stepwise elution technique. The parameters determined from these two independent methods are in c lose agreement. For paclitaxel and cephalomannine, the retention times and peak shapes from plant tissue culture broth experiments are well predicted from rate model simulations using the parameters estimated f rom single-component elution data.