On-line two-dimensional capillary electrophoresis with mass spectrometric detection using a fully electric isolated mechanical valve.

CE is becoming more and more important in many fields of bioanalytical chemistry. Besides optical detection, hyphenation to ESI-MS detection is increasingly applied for sensitive identification purposes. Unfortunately, many CE techniques and methods established in research and industry are not compatible to ESI-MS since essential components of the background electrolyte interfere in ES ionization. In order to identify unknown peaks in established CE methods, here, a heart-cut 2D-CE separation system is introduced using a fully isolated mechanical valve with an internal loop of only 20 nL. In this system, the sample is separated using potentially any non-ESI compatible method in the first separation dimension. Subsequently, the portion of interest is cut by the internal sample loop of the valve and reintroduced to the second dimension where the interfering compounds are removed, followed by ESI-MS detection. When comparing the separation efficiency of the system with the valve to a system using a continuous capillary only a slight increase in peak width is observed. Ultraviolet/visible detection is integrated in the first dimension for switching time determination, enabling reproducible cutting of peaks of interest. The feasibility of the system is successfully demonstrated by a 2D analysis of a BSA tryptic digest sample using a nonvolatile (phosphate based) background electrolyte in the first dimension.

Capillary electrophoresis in two-dimensional separation systems: Techniques and applications.

The analysis of complex samples requires powerful separation techniques. Here, 2D chromatographic separation techniques (e.g. LC-LC, GC-GC) are increasingly applied in many fields. Electrophoretic separation techniques show a different selectivity in comparison to LC and GC and very high separation efficiency. Thus, 2D separation systems containing at least one CE-based separation technique are an interesting alternative featuring potentially a high degree of orthogonality. However, the generally small volumes and strong electrical fields in CE require special coupling techniques. These technical developments are reviewed in this work, discussing benefits and drawbacks of offline and online systems. Emphasis is placed on the design of the systems, their coupling, and the detector used. Moreover, the employment of strategies to improve peak capacity, resolution, or sensitivity is highlighted. Various applications of 2D separations with CE are summarized.

CZE-CZE ESI-MS Coupling with a Fully Isolated Mechanical Valve.

The hyphenation of capillary electrophoresis and electrospray ionization-mass spectrometry is a powerful tool for peptide and protein analysis. It provides high separation power in combination with sensitive and selective detection and the possibility of analyte identification. Unfortunately, many proven capillary electrophoresis methods are not compatible with electrospray-mass spectrometry since several compounds of best separating background electrolytes are interfering in the electrospray ionization. Here, we describe a two-dimensional capillary electrophoresis system using the second dimension as a cleanup stage in order to remove interfering compounds to enable electrospray-mass spectrometry coupling.