Electrospray ionisation principle

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). 

Two techniques that have become preffered for ionisation of proteins/peptides is electrospray ionisation (ESI) and matrix-assisted laser desorption/ionisation (MALDI). Although different combinations of ionisation techniques and mass analyser exist, MALDI usually is coupled with a time-of-flight (TOF) (Figure 7) tube as a mass analyser while ESI is tradionally combined with quadrupole mass analysers. Instruments capable of MS/MS have the ability to select ions of particular m/z ratio from a mixture, to fragment selected ions and to record the precise masses of the resulting fragment ions. If this process is applied to the analysis of peptide ions, in principle the amino acid sequence of the peptide can be deduced. 

Nano-Electrospray Ionisation (nESI) is a variant on ESI which allows much lower flow rates, and therefore allows reduced sample consumption. The principle was developed in the mid-90s, with the primary aim of conpling to HPLC systems ... 

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