SIMPLE-MODEL FOR BLENDING AQUEOUS SALT BUFFERS - APPLICATION TO PREPARATIVE CHROMATOGRAPHY

In preparative chromatography of proteins and other biopolymers, eluti on is frequently achieved by a stepwise or continuous change of the mo bile phase composition, generally denoted as step or linear gradient. The gradient is formed by inline mixing of two aqueous buffers. For pr ediction of peak profiles, examination of the reliability of blending devices and remote control of chromatography controllers a model would be advantageous. This would be most beneficial for ion-exchange chrom atography and hydrophobic interaction chromatography where aqueous buf fers must be blended. Here different salt concentrations are commonly blended. The model is able to describe the delay of onset and the tran sition period for step gradient We developed a model based on the simp le continuously stirred tank reactor model (CSTR) which has been modif ied to include logistic growth. Two parameters have to be estimated; p arameter a is a lumped parameter related to the exponential time const ant and Gaussian broadening. The second parameter, denoted b, describe s the delay inherent to the system. This novel model is compared to a model based on the convolution of a step input with a Gaussian broaden ing and an exponential decay. The predicted values of both models are similar, when compared to experimental data obtained from inline mixin g of two salt buffers. The logistic growth modified CSTR model exhibit ed higher residuals than the convolution model. The beginning of the g radient cannot be approximated in a smooth fashion, since the applied equation contains a sharp inflection. The current model's application is limited to the blending of salt buffers; pH is not a consideration of this model.