Characterization of ammonium chloride derivatives by salt clustering in electrospray mass spectrometry

Efficient clustering of cyclic sulfonium salts applying liquid secondary ion mass spectrometry

Salt-like cluster ions of the ([cation](n)[anion](n-1))(+) type are commonly composed of mono-atomic, inorganic components. Clusters containing organic ions are also known, with nitrogen-centred cations being particularly prominent. However, sulphur-centred analogues, such as organic sulphonium salts, represent a notable exception. Fast atom bombardment and liquid secondary ion mass spectrometry of such compounds show, in general, a low tendency towards the formation of clusters. The present study reveals that sputtering of cyclic sulphonium salts leads to the efficient formation of cluster ions beyond previous observations. Cluster ions are characterised by isotopic pattern analysis and collision-induced dissociation.

Chemometric approach to evaluate the parameters affecting electrospray: application of a statistical design of experiments for the study of arginine ionization

The effects of different experimental parameters on arginine electrospray ionization have been investigated with response surface modelling design. This chemometric technique allows a study of the effects of selected experimental variables and their interactions on the response of an experiment by performing a limited number of analyses. Six variables were studied: methanol content in the liquid phase, formic acid concentration, electrospray voltage, orifice voltage, mobile phase flow rate, and sheath gas flow rate. Signal abundance and signal-to-noise ratio of the protonated molecule and the protonated dimer were measured from the electrospray mass spectra and these four responses were tested by the design. The factor that exhibits the greatest influence on MH+ abundance is shown to be the liquid flow rate whereas the formation of protonated dimer is mainly controlled by the percentage of methanol in the mobile phase. A strong synergic effect of methanol content and formic acid concentration in the liquid has also been demonstrated in the study of noise level. Moreover, the capabilities of the multicriteria optimization method have been demonstrated through a successful prediction of a set of optimal experimental conditions.