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 cellulose (Cuprophan), cellulose acetate, and polyacrylonitrile (PAN) were examined in this system using hydroquinone as the test analyte. The permeability of the membranes to hydroquinone ranged from 1.72 x 10(-6) cm2/s for PAN to 2.97 x 10(-7) cm2/s for cellulose acetate. Determination of the dialysis fibers' recovery as a function of the sample flow velocity resulted in a rapid increase in recovery with increase in flow velocity. The recovery plateaued at high sample velocity. These results show that at low sample velocity diffusion through the sample solution is the rate-limiting step in recovery while at higher velocity transport through the membrane becomes rate limiting. Recovery for all three membrane types plateaued above sample velocities of 0.211 cm/s. This is well below the velocity of most biological fluids in which microdialysis sampling has been applied. This result supports previous reports that an in vitro calibration of microdialysis probes is appropriate for use in hydrodynamic environments in vivo such as the blood and bile.