EXAMINATION OF MICRODIALYSIS SAMPLING IN A WELL-CHARACTERIZED HYDRODYNAMIC SYSTEM

The use of microdialysis sampling was examined in a well-characterized hydrodynamic system. A cross-flow microdialysis probe was designed in which the flow of both the dialysis perfusion solution and the sample solution could be carefully controlled. Dialysis membranes of cellulo se (Cuprophan), cellulose acetate, and polyacrylonitrile (PAN) were ex amined in this system using hydroquinone as the test analyte. The perm eability of the membranes to hydroquinone ranged from 1.72 x 10(-6) cm 2/s for PAN to 2.97 x 10(-7) cm2/s for cellulose acetate. Determinatio n of the dialysis fibers' recovery as a function of the sample flow ve locity resulted in a rapid increase in recovery with increase in flow velocity. The recovery plateaued at high sample velocity. These result s show that at low sample velocity diffusion through the sample soluti on is the rate-limiting step in recovery while at higher velocity tran sport through the membrane becomes rate limiting. Recovery for all thr ee membrane types plateaued above sample velocities of 0.211 cm/s. Thi s is well below the velocity of most biological fluids in which microd ialysis sampling has been applied. This result supports previous repor ts that an in vitro calibration of microdialysis probes is appropriate for use in hydrodynamic environments in vivo such as the blood and bi le.