Electrospray interface for LC-MS

As electrospray is a very soft ionisation technique, the spectra are dominated by molecular ion- or quasimolecular ion-related species. Ionic, nonionic and zwitterionic surfactants are all amenable to the technique. Unlike FAB or LSIMS, electrospray does not suffer from discrimination effects [6] and it is therefore applicable to the analysis of mixtures. Sensitivity is high 10 pg of cationic surfactants can be detected with a good signal-to-noise ratio. The spectrum contains peaks from the intact cation. It has been reported [7] that the limit of detection for positive-ion electrospray is of the order of several femtograms (1 fg = 10 g). 

Anionics typically give negative-ion electrospray spectra corresponding to the intact anion [7]. Such ions are present in the spectra of fatty acids, a-olefin sulphonic acids, and linear alkyl benzenesulphonates [6]. In addition to the intact anion, alkyl sulphates also give ions at mie 97 and 80 as in negative-ions FAB (see section 12.6.3). These correspond to the species SO4 and SOJ. Alkyl sulphonates give the intact anion and the mIe = 80 species. In positive-ion electrospray, anionic surfactants can be detected as clusters with two cations (e.g. two sodium ions). 

Nonionics and zwitterionics can give positive-ion electrospray spectra by cation attachment [7]. 

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Since the first introduction of commercial electrospray interfaces for LC-MS, based on the Fenn design, continuous developments have taken place, resulting in more reliable and robust as well as more efficient interfaces. Some aspects of these developments are briefly discussed here. 

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