Figure 11 Diagram of a typical off-line microdialysis sampling system.

Microdialysis has several advantages as a sampling method. Due to the lowmolecular-weight cutoff of the dialysis membrane, proteins are excluded; this makes possible direct injection of the sample into the LC or CE. Enzymes are also excluded from the sample, obviating the need for enzyme inhibitors to ensure sample integrity. Because there is no net fluid loss, sampling can be done for long periods of time. Last, compounds (drugs, peptides) can be delivered directly to the site of interest to look at local metabolism or pharmacological action.