title: Hydrophobic labeling of amino acids: transient trapping-capillary/microchip electrophoresis.
abstract: Transient trapping (tr-trapping) was developed as one of the on-line sample preconcentration techniques to improve a low concentration-sensitivity in microchip electrophoresis (MCE), providing highly effective preconcentration and separation based on the trap-and-release mechanism. However, a poor performance to hydrophilic analytes limited the applicability of tr-trapping. To overcome this drawback, tr-trapping was combined with a sample labeling using a hydrophobic reagent in CE. Three commercially available fluorescent dyes, fluorescein isothiocyanate, succinimidyl esters of Alexa Fluor 488 and BODIPY FL-X, were tested as derivatization reagents to increase the hydrophobicity of amino acids (AAs) that were undetectable due to no fluorescence/UV-absorbance. As a result, it was confirmed that BODIPY labeling allowed various AAs to be analyzed in tr-trapping-micellar electrokinetic chromatography (tr-trapping-MEKC) by the increase in the hydrophobicity. In tr-trapping-MEKC, both the improvement of the resolution and 106-125-fold enhancements of the detectability of labeled AAs were achieved relative to the conventional capillary zone electrophoresis. The limit of detection of labeled phenylalanine was improved from 800 to 5 pM by applying tr-trapping-MEKC. In tr-trapping-microchip MEKC, furthermore, an 80-160-fold enhancement of the peak intensity and a baseline separation was also achieved within 30 s. These results clearly demonstrate that the tr-trapping technique with hydrophobic labeling will make CE/MCE more sensitive for various analytes.
authors.affiliation: Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto, Japan. sueyoshi@anchem.mc.kyoto-u.ac.jp
authors.forename: Kenji
authors.initials: K
authors.lastname: Sueyoshi
authors.forename: Kota
authors.initials: K
authors.lastname: Hashiba
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kawai
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Kitagawa
authors.forename: Koji
authors.initials: K
authors.lastname: Otsuka
mesh_terms: D000596:Amino Acids / Q000737:chemistry* / Q000302:isolation & purification; D046209:Electrophoresis, Microchip / Q000379:methods*; D005456:Fluorescent Dyes / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D012680:Sensitivity and Specificity
chemical_list: D000596:Amino Acids; D005456:Fluorescent Dyes