Comparison of conventional, narrow-bore and capillary liquid chromatography/mass spectrometry for electrospray ionization mass spectrometry: practical considerations

Electrospray ionization (ESI) is nowadays the most important technique for on-line liquid chromatography/mass spectrometry (LC/MS) coupling. Different ESI probe designs including the microESI and pneumatically assisted ESI (ionspray) interfaces allow the introduction of sample at flow-rates ranging from a few hundred nl min−1 to 1–2 ml min−1. In this paper, an overview of the different LC/ESIMS devices is presented from the point of view of their flow compatibility. Several parameters for LC/ESIMS miniaturization and its effects on sensitivity are considered from the practical point of view. Low-flow ESI requires the use of narrow-bore and capillary columns. Sample preconcentration microdevices are recommended in order to circumvent some miniaturization drawbacks such as the low optimum injection volume and the low column capacity. Some considerations on fused-silica microcolumn and microESI needle construction are also presented.