Achievements electrospray ionisation

As described in 2.2.3.1, Principles of Assay , tHcy must be produced by chemical reduction, which is achieved in the method described here by dithiothreitol. tHcy is analysed by HPLC separation followed by electrospray ionisation and then separation of the ionised molecule in the first mass spectrometer, then fragmentation into a specific ion fragment in the second. Quantification is based on comparison of the signal from natural Hey (transition m/z 135.9 —< m/z 89.9) with that of the stable isotope internal standard (transition m/z 139.9 —< m/z 93.9). 

Electrospray ionisation is achieved at atmospheric pressure, the mass analyser, however, operates under high vacuum. A special interface is therefore necessary to transfer the ions from the ionisation chamber into the mass spectrometer. A schematic of such an interface is shown in Fig. 4.14. Usually a zone of intermediate pressure separates the ionisation chamber and the mass analyser. The liquid sample together with a curtain or nebulising gas is introduced into the heated ionisation chamber. An electrospray is generated by applying a potential difference between the needle and the opposite interface plate. A small proportion of the desolvated analyte ions exit the ionisation chamber through a submillimeter orifice and enter the zone of intermediate pressure. The analyte ions then pass via another small orifice into the mass analyser. This is usually a quadrupole which is operated under high vacuum. 

Williams, D.K. Hawkiidge, A.M. Muddiman, D.C. Sub-ppm mass measurement accuracy of intact proteins and product ions achieved using a dual electrospray ionisation quadrupole FT-ICR mass spectrometer. J. Am. Soc. Mass Spectrom. 2007,18 ), 1-7. Witt, M. Fuchser, J. Baykut, G. FT-ICR mass spectrometry with NanoLC/microelec-trospray ionization and MALDI Analytical performance in peptide mass fingerprint analysis. /. Am. Soc. Mass Spectrom. 2003,14(6), 553-561. 

These have also been characterised by GC-MS and electrospray ionisation [28]. It was shown that epoxy ring opening was achieved at low temperatures and within short reaction times. Several reactions were found to occur simultaneously and were involved in the early polymerisation process, leading to fast catalyst deactivation in solution, chlorination of 3-glycidoxyproply-tri-methoxysilane organic groups and titanium dispersion inside precursor sols. 

Electrospray has been successful for numerous azo dyes that are not ionic salts. Several anthraquinone dyes have been analysed by LC-ESI-MS [552]. Electrospray achieves the best sensitivity for compounds that are precharged in solution (e.g. ionic species or compounds that can be (de)protonated by pH adjustment). Consequently, LC-ESI-MS has focused on ionic dyes such as sulfonated azo dyes which have eluded analysis by particle-beam or thermospray LC-MS [594,617,618]. Techniques like LC-PB-MS and GC-MS, based on gas-phase ionisation, are not suitable for nonvolatile components such as sulfonated azo dyes. LC-TSP-MS on... 

---