We investigate eight 1‐alkylpyridinium‐based ionic liquids of the form [CnPy][A] by using X‐ray photoelectron spectroscopy (XPS). The electronic environment of each element of the ionic liquids is analyzed. In particular, a reliable fitting model is developed for the C 1s region that applies to each of the ionic liquids. This model allows the accurate charge correction of binding energies and the determination of reliable and reproducible binding energies for each ionic liquid. Shake‐up/off phenomena are determinedfor both C 1s and N 1s spectra. The electronic interaction between cations and anions is investigated for both simple ionic liquids and an example of an ionic‐liquid mixture; the effect of the anion on the electronic environment of the cation is also explored. Throughout the study, a detailed comparison is made between [C8Py][A] and analogues including 1‐octyl‐1‐methylpyrrolidinium‐ ([C8C1Pyrr][A]), and 1‐octyl‐3‐methylimidazolium‐ ([C8C1Im][A]) based samples, where X is common to all ionic liquids.

RATIONALE:Lipids are typically analysed in negative ionisation mode in desorption electrospray ionisation mass spectrometry (DESI-MS), which can result in reduced sensitivity. In this study we examine the use of dicationic compounds as reactive DESI-MS agents to detect a range of lipid standards from the surface in positive ionisation mode. METHODS: Nine dicationic compounds were tested for their ability to detect seven representative lipid species (palmitoleic acid, linoleic acid, phosphatidic acid (34:1), phosphoethanolamine (34:2), phosphatidylglycerol (34:1), phosphatidylserine (36:1), and phosphoinositol (34:2)) with a 2D DESI source on hydrophobic surfaces. Two different solvent systems (methanol/chloroform (1:1) and methanol) were tested with each dicationic compound, with the DESI-MS analysis performed in the positive ionisation mode. RESULTS: Most of the dications tested were able to form stable ion-pairs with the negatively charged lipid species when analysed from the surface with DESI-MS, and were detected readily in positive ionisation electrospray mode as singly charged species. The optimal solvent system was found to be methanol. The dicationic compound [C 6 (C 1 Pyrr) 2 ][Br] 2 was found to enhance the detection of palmitoleic acid (638%), linoleic acid (304%) and phosphoethanolamine (269%) compared with the negative ionisation mode. CONCLUSIONS: We demonstrate the first successful application of dicationic compounds in DESI-MS for the ambient surface detection of model lipids in positive electrospray ionisation mode. Dicationic compounds could potentially be used as reactive DESI-MS agents to improve the ambient detection of a number of negatively charged analytes.

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Novel scan routines, termed ‘multiple‐scan monitoring’ cycles, have been developed for the rapid sequential acquisition of data from two or more scan types using ion‐trap mass spectrometry. These cycles allow data to be acquired from multiple‐scan functions with a cycle time compatible with combined chromatography/mass spectrometry and other sample introduction methods. Multiple‐scan monitoring is illustrated for the measurement of the components of a test mixture, and for the determination of sulphamethazine and tetrachlorodibenzo‐p‐dioxin.

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