Dual-Gradient Capillary Electrochromatography by Varying the Mobile Phase Composition and Applied Voltage

Abstract

Dual-gradient capillary electrochromatography (DG-CEC) was developed to provide superior performance with regard to the separation of ionized analytes; in this method, both the eluent composition and the applied voltage are varied during the separation procedure. As for the gradient in the eluent composition, a shift in the pH is employed to control not only the electrophoretic mobility, but also the retention factor of the analytes. The dual-gradient method was shown to be effective in increasing the resolution and reducing the chromatographic period of ionized analytes. Fourteen kinds of o-phthalaldehyde labeled amino acids were separated within 8 min using DG-CEC with multistage enlargement in the applied voltage. The separation efficiency increased particularly for highly retained amino acids in the dual-gradient, as compared to those in the ordinary single-gradient for the eluent.

Analyte zone sharpening in pressurized capillary electrochromatography based on electrophoretic migration under a heterogeneous field

“…In this condition, the cationic peptides migrated toward the outlet, in which ACN content was relatively higher and the interaction with the stationary phase was slightly enhanced. The electrophoretic migration in the linear gradient field would reduce the peak width in a similar fashion to our previous studies .…”

“…As a consequence, the analyte at the front end was overtaken by that at rear end and the peak width was reduced, or focused. However, in our previous study, the magnitude of the reduction in the peak width was approximately half at the maximum, or the peak height increased approximately twice as much .…”

“…The apparatus for pCEC used was similar to the arrangement in our previous report . Briefly, the apparatus is composed of two pumps (LC‐10ADvp, Shimadzu, Kyoto, Japan), a static mixer (volume: 0.1 mL, Shimadzu), two laboratory‐made splitters, two resistance tubes (fused‐silica capillary, id 0.05 mm, od 0.375 mm, length 500 mm, supplied by GL Science, Tokyo, Japan), a UV detector (CE‐2075, Jasco, Tokyo, Japan), an injector (model 7520, Rheodyne, CA), a high‐voltage power supply (HCZE‐30PN0.25, Matsusada Precision, Shiga, Japan), and a laboratory‐made capillary column (id 0.15 mm, od 0.375 mm).…”

“…It should be noted that gradient elution can be regarded as a method that provides a heterogeneous field to a column, and electrophoretic migration under the same can potentially suppress band broadening if voltage was applied along this column. We have reported reducing peak widths for amino acids and peptides in reversed‐phase pressurized capillary electrochromatography (RP‐pCEC) with a linear gradient elution . In this case, the migration velocity of the analyte was varied dependently on the longitudinal portion of the column, i.e.…”

Zone Sharpening of Peptides in Pressurized Capillary Electrochromatography Using Dynamic pH Junction

“…12 Therefore, on-capillary concentration methods for CE should be applicable to pCEC and may be potentially useful for reducing the sample zone width spread in the column. 13,14 Recently, we reported on analyte zone sharpening for angiotensins in hydrophilic interaction capillary electrochromatography using a mobile phase containing perchloric acid. 15 In this previous study, we revealed that the gradient elution provided a significantly high conductive zone, which was produced by desorption of perchloric anions from the stationary phase.…”