Simple and effective label-free capillary electrophoretic analysis of sugars by complexation using quinoline boronic acids

An effective separation and detection procedure for sugars by capillary electrophoresis (CE) using a complexation between quinolineboronic acid (QBA) and multiple hydroxyl structure of sugar alcohol is reported. We investigated the variation of fluorescence spectra of a variety of QBAs with sorbitol at a wide range of pH conditions and then found that 5-isoQBA strongly enhanced the fluorescence intensity by the complexation at basic pH conditions. The other sugar alcohols having multiple hydroxyls also revealed the enhancement of the fluorescence intensity with 5-isoQBA, whereas the alternation of the intensity was not found in the sugars such as glucose. After optimization of the 5-isoQBA concentration and pH of the buffered solution in CE analysis, 6 sugar alcohols were successfully separated in the order based on the formation constants with 5-isoQBA, which were calculated from the variation of the fluorescence intensity with each sugar alcohol and 5-isoQBA. Furthermore, the limits of detection for sorbitol and xylitol by the CE method were estimated at 15 and 27 μM, respectively.