Hongping Wei

1, 3-Dialkylimidazolium-based room-temperature ionic liquids as background electrolyte and coating material in aqueous capillary electrophoresis

The 1-ethyl-3-methylimidazolium (EMIM) cation was found to have constant mobility of 4.5 x 10(-4) cm2 V(-1) s(-1) over the pH range of 3 to 11. The electroosmotic flow of bare silica capillary was reversed by the covalently bonded room-temperature ionic liquid (RTIL) coating. With run buffer of 5 mM EMIM (pH 8.5), NH4+ in human urine was separated from the K+ matrix and was detected to be 0.37 +/- 0.012%. K+, Na+, Li+, Ca2+, Mg2+ and Ba2+ were baseline separated in RTIL-coated capillary with run buffer of 10 mM EMIMOH-acetic acid at pH 5, and the concentration of the above ions in a red wine were detected to be 907, 27.9, 0, 71.0, 83.4 and 31.1 microg/ml, respectively. The RTIL-coated capillary showed stable electroosmotic flow for at least 80 h in the run buffer.

Separation of ionic liquid cations and related imidazole derivatives by α-cyclodextrin modified capillary zone electrophoresis

The separation and detection of 1-alkyl-3-methylimidazolium, including isomers, and related imidazole derivatives was performed by alpha-cyclodextrin (alpha-CD) modified capillary zone electrophoresis. The separations were carried out in a running buffer comprising 5.0 mM triethylamine and 2.0 mM alpha-CD adjusted to pH 4.5 by acetic acid. All the analytes were baseline separated within 8 min and the detection limits (signal-to-noise ratio = 3) ranged between 0.42 and 1.36 ppm. The method showed good linearity (within 3-50 times the detection limits, r > 0.99) and reproducibility (relative standard deviation < 0.8% for migration times and < 3% for peak areas), which should make it suitable for routine analysis. It was employed in detecting impurities in commercial chemicals, and 0.27% 1-methylimidazole in 1-ethyl-3-methylimidazolium chloride and 0.55% imidazole in 2-ethylimidazole were found. In addition, it was employed in process analysis during synthesis of ionic liquids and demonstrated a potential to provide information on the reaction mechanism.

Rugged gap reactor device for postcolumn fluorescence detection in capillary electrophoresis

In this paper, the construction and performance of a rugged device for postcolumn derivatization in capillary electrophoresis (CE) are described. The device was based on a gap design, and a gap with a very small distance (<3 μm, estimated under microscope) could be easily constructed without micromanipulation. Addition of derivatizing reagents into the reaction capillary was attributable to gravity flow. The concentration of derivatizing reagents can be controlled through manipulating the electroosmotic flow in the reaction capillary and the height of the liquid levels from the derivatizing reagents to the buffer reservoirs. The device has been applied in fluorescence detection of amino acids using a mixture of o-phthaldialdehyde/2-mercaptoethanol as derivatizing reagent. Theoretical plate numbers for 11 amino acids separated in a pH 9.5 borate buffer were obtained in the order of 40 000-250 000. The detection limit for glycine (S/N = 2) was found to be 6.7 × 10(-)(7) mol/L using a commercial HPLC fluorescence detector modified for CE. Free amino acids in a wine sample were also determined. Because the device is quite stable, we believe that it can be used routinely in analytical laboratories.

Capillary electrophoretic analysis of cyclodextrins with dynamic fluorescence labeling and detection

Abstract The use of 8-anilinonaphthalene-1-sulfonic acid (8,1-ANS) as buffer additive in the capillary electrophoretic separation of cyclodextrins (CDs) was investigated. Better detection sensitivity was obtained for α- and γ-CDs than with previously reported capillary electrophoretic methods. Increasing the concentration of 8,1-ANS improved resolution and sensitivities for α-, β- and γ-CDs, while decreasing the pH of the background electrolyte can improve sensitivities. Detection limits for α-, β- and γ-CDs were determined to be 60, 20 and 7 μ M , respectively. The formation constants of CD–8,1-ANS complexes at pH 6 were also measured by capillary electrophoresis. Finally the specificity of amyloglucosidase to CDs was analyzed as a practical application of this method.