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• The ionicity of ILMs was tested by experimental and calculation methods. • The ionicity was found to be varied between matrices and driven by several factors. • The intermolecular interactions were found to have a great impact on ionicity. • The retro -proton transfer at a high temperature was determined. Ionic liquid matrices (ILMs) have been applied for MALDI-MS analysis for more than 20 years. Despite this, there is still insufficient knowledge regarding their properties. In this work, we tested the ionicity of selected ILMs and discussed their impact on the MALDI process. The targets were the following mixtures: CHCA/TEA, FER/TEA, HABA/α-MBA, 2,5-DHB/α-MBA (CHCA - α-cyano-4-hydroxycinnamic acid, FER – ferulic acid, HABA − 2-(4-hydroxyphenylazo)benzoic acid, 2,5-DHB − 2,5-dihydroxybenzoic acid, TEA – triethylamine, α-MBA - α-methylbenzylamine). These are ILMs which in our previous study showed liquidity at room temperature. We decided to apply several empirical and theoretical techniques due to the complexity of the problem. Thermogravimetric analysis (TGA) with IR was used to test the process at a higher temperature (simulation of a laser shot). 1H NMR was used for the determination in pure ILMs of intermolecular interactions, which have a high impact on ionicity. Conductivity and rheological measurements were performed to determine the Walden plot, from which the excess of ionicity can be concluded. DFT calculations were used to support the statements of dissociation processes in the gas phase and solution. The auto-ionization of matrices in MALDI was also tested. The interpretation of the Walden plot shows that HABA/α-MBA is a very good ionic liquid, which can be derived from a proposed "pedal motion"-like mechanism. The ionicity of other matrices was reduced because of intermolecular interactions (proved by TGA-IR and 1H NMR). The MALDI-MS analysis shows that the obtained mass spectra, namely the base peaks, depend on amine gas proton affinity. Furthermore, the DFT calculation results and the TGA-IR analysis support the mechanism of retro -proton transfer after the laser shot in the gas phase. Finally, it was concluded that the four tested ILMs are differentiated in ionicity, but its extent has no impact on the auto-ionization of the matrix. [ABSTRACT FROM AUTHOR]

• The number of small molecules analyzed by MALDI MS using ILM is relatively low. • The highlighted advantages were reported for rather low number of ILMs. • The lower time of MALDI analysis can be achieve thanks to the ILMs application. • Often higher laser energy was needed for effective ionization supported by the ILMs. • Guidelines for the selection of ILMs for a specific task are awaiting to be presented. Ionic liquid matrices (ILMs) were introduced almost 20 years ago as alternatives to crystal matrices for MALDI MS analysis. They are protic ionic liquids synthesized by mixing conventional acidic MALDI matrices with an equimolar number of organic amines. They have certain advantageous attributes, such as: i. high homogeneity of the matrix + sample mixture, which increases the shot-to-shot reproducibility, ii. reducing the background on mass spectra, which is why molecules with low masses can be analyzed, and iii. the possibility of the quantitative analysis of small molecules. This review aims to present updated reports on the applicability of ILMs for the quantification of small molecules, and to critically discuss the features therein. The number of reports presenting quantitative analysis using ILMs is relatively small, despite the wide range of synthesized ILMs. Various representatives of small peptides, amino acids, pharmaceuticals, drugs, oligosaccharides, alkaloids and toxins were analyzed using ILMs based on DHB and CHCA acids. Furthermore, ILMs were found to be applicable for the imaging and mapping of lipids and small peptides. Even relatively similar ILMs vary from one another due to their ionization potential (intensity of signals in positive and negative ion extraction mode, fragmentation rate, adduct formation). Currently, there are no guidelines for the selection of ILMs for a specific task, which would appear to be a milestone in the application of ILMs for MALDI MS. [ABSTRACT FROM AUTHOR]

In the presented study, the applicability of four sorbent materials (active carbon, neutral alumina, Primary and Secondary Amines (PSA), and Florosil) applied on top of a polymeric Strata-X column was tested to improve the solid-phase extraction of 15 analytes (pharmaceuticals and estrogens) from water. Deionized water and water fortified by humic acids (representatives of dissolved organic matter) were the tested matrices. The effect of water acidification was tested as well. The values of recovery show that sorbents often have different sorption features towards pharmaceuticals with acidic and basic functional groups. PSA shows sorption towards humic acids, thereby can minimize the matrix effect obtained during final quantification by chromatographic techniques coupled with mass spectrometry. The slight sorption of basic pharmaceuticals to humic acids was found out. Finally, a mixture of PSA and alumina was used, and the validated SPE-GC/MS(SIM) method was applied for raw and treated wastewater. A triple-sorbent solid-phase extraction cause lower matrix effect compared to the previous study. This small innovation in the SPE procedure (without any significant cost enhancement and extension of the duration) can have an impact on the quantification of the pharmaceuticals and estrogens, and improve the reliability of the results. • Four sorbents were applied on top of a polymeric SPE column. • Active carbon was discarded; Florosil showed sorption towards basic analytes. • PSA effectively adsorbed humic acids, reducing the matrix effect. • Humic acids affected the recovery of basic analytes (β-blockers, antidepressants). • Finally, Strata-X + PSA + Alumina were used for the screening of analytes in wastewater. [ABSTRACT FROM AUTHOR]