Hyphenated CE techniques

Hyphenation in capillary electrophoresis is still in its infancy. Critical aspects of CE hyphenation include the minute volumes of sample injected (typically a few nL) and small flow-rates (in the order of nLmin-1). Interfaces are not commercially available. CZE-UV can be used for the analysis of higher polyamide oligomers in HF1P solution [859]. A solvent elimination design with nebuliser has been described for CE-FTIR and CEC-FTIR coupling absolute detection limits are hundreds of pg [860]. An advantage of CE-FTIR is that analytes may be detected and identified without derivatisation. CE(C)-NMR [861-863] is advancing rapidly. 

Principles and Characteristics The main reasons for hyphenating MS to CE are the almost universal nature of the detector, its sensitivity and the structural information obtainable, including assessment of peak purity and identity. As CE is a liquid-phase separation technique, coupling to the mass spectrometer can be achieved by means of (modified) LC-MS interfaces. Because of the low flow-rates applied in CE, i.e. typically below lOOnLmin-1, a special coupling device is required to couple CE and the LC-MS interface. Three such devices have been developed, namely a 

Although electrospray ionisation has advantages for studies of ionic and very polar molecules, APCI is the preferred ionisation method for many other compounds - in that it provides better sensitivity and has advantages for quantitative studies. CE-APCI-MS studies were conducted on both QQQ and QITMS instruments [887]. 

The combination of CE with continuous-flow fast atom bombardment (CF-FAB-MS) requires the use of an interface, because of the incompatibility of the CF-FAB process and CE for liquid flow [888], The CF-FAB source requires a solvent, usually water/glycerol (95-5 v/v), which is maintained at a steady flow-rate of 2-15mLmin 1. Flow-rate in CE does not exceed 1 nLmin-1. 

Variations may also be introduced at the CE end of the coupling. CZE is the most widely practised mode of CE. Nanospray CZE-ESI-MS [889], 

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