Review: Sample Concentration Based on Inclusion of Organic Solvents in Capillary Zone Electrophoresis

Capillary electrophoresis, as an analytical tool for drugs, offers several advantages for pharmaceuticals and clinical applications; however, it suffers from poor detection limits. Concentration on the capillary (stacking) improves greatly this problem and is very easy to perform. One of the simple and practical methods to perform stacking is dissolving the sample in organic solvents and injecting a large volume of sample on the capillary. This leads to concentration of the sample 10-30 folds directly on the capillary, removes the excess of proteins found in biological fluids and overcomes the deleterious effects of salts. The stacking can be performed in both the hydrodynamic and electroinjection. This stacking brings the detection limits of the CE closer to that of the HPLC. The mechanism, practical applications, different factors, and optimum conditions for this type of stacking are reviewed and discussed.