Flow Counterbalanced Capillary Electrophoresis Using Packed Capillary Columns: Resolution of Enantiomers and Isotopomers

Microchip-Based Electrophoretic Separations with a Pressure-Driven Backflow

It is well known that the resolving power of capillary zone electrophoretic separations may be improved with an increase in the applied electric field strength and separation time. While large electric fields may be realized in short analysis channels commonly employed in microfluidic systems, this experimental design is not suitable for achieving long separation times. In this chapter, we describe the use of a steady and/or a periodic pressure-driven backflow to increase the separation time in short microchannels thereby enabling the analysis of closely related species on microchip devices. The reported backflow was realized in our assays using an on-chip pressure-generation capability that relied on the partial blockage of electroosmotic flow around a junction of two glass channel segments having different depths. Although the noted strategy led to additional band broadening in the system, the resolving power of our device was observed to substantially improve upon introduction of the reported steady/periodic pressure-driven backflow for analysis channels shallower than 5 μm.

Number of theoretical plates achievable by a toroidal capillary electrophoresis system

The ability of a method and instrument to separate very similar compounds is related to the "plate number," a number indicating performance. The resolution between two neighboring peaks is proportional to the square root of the plate number. Currently available commercial capillary electrophoresis instruments easily reach plate numbers of a few million. In the present work, a capillary electrophoresis system with a toroidal platform is proposed and theoretically studied with the goal of extending the achievable plate number. In this new system, electrophoresis occurs in a nonstop continuous circulating mode within a closed loop capillary (toroid). Plate numbers upwards of one billion are theoretically predicted. This could resolve hundreds of unseparated mixtures of stereoisomers and other analytes that remain without a method for their analysis.

Enhanced neuropeptide profiling via capillary electrophoresis off-line coupled with MALDI FTMS

An off-line interface incorporating sheathless flow and counter-flow balance is developed to couple capillary electrophoresis (CE) to matrix-assisted laser desorption ionization Fourier transform mass spectrometry (MALDI FTMS) for neuropeptide analysis of complex tissue samples. The new interface provides excellent performance due to the integration of three aspects: (1) A porous polymer joint constructed near the capillary outlet for the electrical circuit completion has simplified the CE interface by eliminating a coaxial sheath liquid and enables independent optimization of separation and deposition. (2) The electroosmotic flow at reversed polarity (negative) mode CE is balanced and reversed by a pressure-initiated capillary siphoning (PICS) phenomenon, which offers improved CE resolution and simultaneously generates a low flow (<100 nL/min) for fraction collection. (3) The predeposited nanoliter volume 2,5-dihydroxybenzoic acid (DHB) spots on a Parafilm-coated MALDI sample plate offers an improved substrate for effective effluent enrichment. Compared with direct MALDI MS analysis, CE separation followed by MALDI MS detection consumes nearly 10-fold less sample (50 nL) while exhibiting 5-10-fold enhancement in S/N ratio that yields the limit of detection down to 1.5 nM, or 75 attomoles. This improvement in sensitivity allows 230 peaks detected in crude extracts from only a few pooled neuronal tissues and increases the number of identified peptides from 19 to 43 (Cancer borealis pericardial organs (n = 4)) in a single analysis. In addition, via the characteristic migration behaviors in CE, some specific structural and chemical information of the neuropeptides such as post-translational modifications and family variations has been visualized, making the off-line CE-MALDI MS a promising strategy for enhanced neuropeptidomic profiling.

Advances in chiral separation using capillary electromigration techniques

This review gives an overview of recent developments in CZE, EKC, and CEC covering the literature since the year 2004. Since there appeared a special issue on applications, this review focuses on the progress in electromigration techniques and new methodological developments. New techniques, new chiral selectors as well as new chiral stationary phases for CEC are discussed.

Counter-flow gradient electrofocusing

Counter-flow gradient electrofocusing techniques are methods whereby a combination of electrophoresis and a bulk solution counter-flow is used to accumulate or focus analytes at stationary points along a separation column. This review first describes the various forms of counter-flow gradient electrofocusing that have been demonstrated in the literature and then compares figures of merit for counter-flow focusing methods and conventional CE methods. In an effort to compare the concentration enhancement of the various focusing techniques against each other, as well as of stacking methods, the parameter of analyte-accumulation velocity is introduced and employed to normalize the efficacy of the techniques.

Highly efficient protein separations in capillary electrophoresis using a supported bilayer/diblock copolymer coating

A surfactant/polymer wall coating consisting of the doubly chained cationic surfactant dimethyldioctadecylammonium bromide (DODAB) and polyoxyethylene (POE) 40 stearate is investigated. The coating is formed by simply rinsing a capillary with a solution containing DODAB and POE 40 stearate. The resultant coating is semi-permanent--demonstrating stable electroosmotic flow (EOF) even after a 60 min high pressure rinse with buffer. The EOF (-0.45+/-(0.23) x 10(-4) cm(2) V(-1) s(-1) at pH 7.4) is suppressed by more than a factor of ten compared to that observed for DODAB alone. Model protein mixtures were separated over a pH range of 3-10 with efficiencies of up to greater than 1 million plates/m for the basic proteins cytochrome c, lysozyme, ribonuclease A and alpha-lactalbumin, and the acidic proteins insulin chain A, trypsin inhibitor, and alpha-chymotrypsinogen A. Migration time reproducibility was 0.5-4.0% from run to run and 0.6-4.3% from day to day. Protein recoveries with this coating ranged from 84% to 97%.