For affinity capillary electrophoresis (ACE), a novel capillary partially filled with an affinity ligand-encapsulated hydrogel using sodium alginate (SA) was prepared. Alginate hydrogel (AH) can be easily formed by adding a calcium ion into an SA solution and encapsulate proteins with maintaining their affinity. An SA solution containing avidin was partially injected into the capillary filled with a background solution (BGS) containing calcium dichloride, then an appropriate voltage was applied to introduce the calcium ion into the SA solution zone for the hydrogelation. The encapsulation of avidin by the formed AH was expected. To clarify the formation of the avidin-encapsulated hydrogel, a sample solution containing biotin was analyzed in the prepared capillary. In repeated analyses without refreshing the hydrogel, biotin was not detected due to a strong interaction with avidin at the first two runs, whereas it appeared after the third run. These results suggested the saturation of the binding site of the encapsulated avidin with the introduced biotin. Consequently, affinity ligands can be encapsulated successfully by the AH with maintaining their affinity.
As for carbohydrate analyses by capillary electrophoresis, we focused on the ACE analysis using quinolineboronic acids (QBAs) which form complexes with cis-diol compounds like most carbohydrates. In a BGS containing QBAs, the complexation provides the variations of both the fluorescence intensity and the apparent electrophoretic mobility of the complex from those of native carbohydrates, resulting in both the label-free fluorescence detection and selective separation of carbohydrates. As a result, nine carbohydrates, i.e., sorbitol, mannitol, galactitol, catechol, galactonic acid, arabitol, xylitol, meso-erythlitol, and mannose, was separated in a phosphate buffer containing 5-isoQBA, which indicated the successful detection and separation of these carbohydrates without any derivatization.