Diffusion and calibration properties of microdialysis sampling membranes in biological media

The diffusion and calibration properties for three commercially available microdialysis membranes (polycarbonate-polyether (PC), polyacrylonitrile (PAN), and cuprophan (CUP)) were evaluated. The analytes studied had molecular weights between 94 (phenol) and 1355 (vitamin B12). For each analyte-membrane pair, an effective membrane diffusion coefficient was calculated. Effective membrane diffusion coefficients varied considerably between the microdialysis membranes. For Vitamin B12, CUP and PAN membranes gave relative recovery values of greater than 20% at 0.5 microl min(-1), while the PC membrane had a 1% recovery. When backpressure was applied. PC and PAN membranes exhibited more ultrafiltration than CUP membranes. Ultrafiltration did not affect analyte relative recovery through either PC or PAN membranes. Effective membrane diffusion coefficients were not significantly altered for some membrane-analyte combinations when exposed to 4% bovine serum albumin or 0.3% fibrinogen. These data suggest that reductions in relative recovery during long-term microdialysis sampling experiments may be due to other physiologically relevant proteins or to tissue reactions near the dialysis membrane.