Membrane characterisation and performance of microdialysis probes intended for use as bioprocess sampling units

Microdialysis probes equipped with different membranes types, polycarbonate, polyamide, cuprophan (regenerated cellulose), and three different polysulfones, were characterised intended for use as bioprocess sampling units. Quantitative and qualitative analysis of the dialysate composition was made by column liquid chromatography with refractive index detection. The dialysis performance of four alcohols and four carbohydrates was investigated in both standard (pure) and complex solutions by measuring the relative recovery (RR). The RR values of the analytes in a standard solution as a function of the flow-rate of the perfusion liquid are presented for the different membranes. Sampling in the presence of proteins or peptides resulted in lower RR values for the carbohydrates, especially using polysulfone membranes, whereas the dialysis performance for the alcohols was less affected, probably due to additional membrane transport mechanisms available for the alcohols. However, when the alcohols were analysed in the presence of spent sulphite liquor (SSL), a waste water from the pulp industry with a very complex composition, the RR values decreased substantially, in some cases by more than 50%. The decrease is presumably due to the combined effect of adsorption of matrix components onto the membrane surface, and binding of the analytes to compounds in the SSL. It is further shown that the transport of matrix components over the different membranes is more dependent on the porosity and chemical structure of the membranes than on their cut-off. Some preliminary results about the possibility of autoclaving the different membranes are also presented.