CAPILLARY ELECTROPHORESIS MASS-SPECTROMETRY

As an on-line separation method, capillary electrophoresis (CE)-mass spectrometry (MS) distinguishes analytes by both their differences in electrophoretic mobilities and structural information. CE-MS combines the advantages of CE and MS so that information on both high separation efficiency and molecular masses and/or fragmentation can be obtained in one analysis. During the past few years CE-MS has undergone significant development both in instrumentation and application. Several ionization methods have been used for CE-MS. These include electrospray ionization, ion spray or pneumatically assisted electrospray ionization, and continuous-flow fast atom bombardment. The direct coupling of CE to desorption MS has not yet been reported, although publications have appeared on the off-line coupling of CE with matrix-asssisted laser desorption ionization and (252) Cf plasma desorption MS using fraction collection. Numerous new applications of CE-MS have been published in the areas of biological sciences, pharmaceutical and drug metabolism, and environmental analysis. The majority of applications of CE-MS have been in the field of biological and biochemical studies. Several limitations associated with CE-MS have precluded the technique being widely accepted for routine analysis. The major limitation is its relatively poor concentration sensitivity. The concentration detection limits of currently available CE-MS instrumentation are too high for most real-world applications. Other drawbacks with CE-MS include the fluctuation in analyte migration time and limitations in electrolyte selections. Approaches to improve the concentration sensitivity of CE-MS include on-line preconcentration either by capillary isotachophoresis or chromatographic methods. Another solution to increasing the sensitivity of CE-MS is the development of alternative types of mass spectrometers which offer the potential for greater sensitivity, such as ion trap, Fourier transform ion cyclotron resonance, and time-of-flight (TOF) mass spectrometers. Coated capillaries are useful in improving separation efficiencies of biomolecules by minimizing their adsorption onto the CE capillary walls. At present, CE-MS is still not generally considered for routine analysis mainly due to its limited concentration sensitivity. As a complementary separation method to LC-MS with extremely high efficiency, CE-MS has the potential for wide acceptance in the future. The popularity of CE-MS will continue to grow, as more sensitive MS instrumentation and CE-MS interface are developed.