MICELLAR ELECTROKINETIC CHROMATOGRAPHY MASS-SPECTROMETRY

The combination of micellar electrokinetic chromatography (MEKC) with mass spectrometry (MS) is very attractive for the direct identificatio n of analyte molecules, for the possibility of selectivity enhancement , and for the structure confirmation and analysis in a MS-MS mode. The direct coupling of MEKC with MS can be hazardous due to the effect of nonvolatile MEKC surfactants on MS performance, including the loss of analyte sensitivity and ion source contamination. The possibility of off-line coupling between MEKC and matrix-assisted laser desorption/io nization (MALDI)-MS remains to be investigated. Various approaches for on-line coupling MEKC with electrospray ionization (ESI)-MS, includin g the use of high-molecular-mass surfactant, an electrospray-chemical ionization (ES-CI) interface, a voltage switching and buffer renewal s ystem, partial-filling micellar plug and anodically migrating micelles , are reviewed and evaluated. The use of an ES-CI interface is most pr omising for routine operation of on-line MEKC-MS under the influence o f nonvolatile salts and surfactants. The use of a high-molecular-mass surfactant allows the formation of a micellar phase at very low surfac tant concentrations and avoids the generation of a high level of backg round ions in the low m/z region. Alternatively, the application of a partial-filling micellar plug and anodically migrating micelles elimin ate the introduction of MEKC micelles into the ESI-MS system. It is po ssible to directly transfer the conventional MEKC separations to parti al-filling MEKC-ESI-MS and MEKC-ESI-MS using anodically migrating mice lles without any instrument modifications. (C) 1997 Elsevier Science B .V.