Cold‐spray ionization mass spectrometry of the choline chloride‐urea deep eutectic solvent (reline)

Abstract

Cold‐Spray Ionization mass spectrometry (CSI‐MS) that can be compared to an electrospray ionization (ESI) source acting with a nebulizing gas cooled by liquid nitrogen is used for analyzing reline as Deep Eutectic Solvent (DES). The association of cholinium chloride salts with urea molecules is evidenced in negative CSI‐MS through the chloride adduct formation. The structure of the supramolecular assemblies forming the reline ions that are observed on CSI mass spectra is rationalized by chemical quantum calculations. The theoretical studies indicate that the ionic network organization is only supported by a maximization of hydrogen bonds of the chlorides with the hydroxyl and methyl moieties of the cholinium cations and the amino groups of urea. The studies of gas‐phase fragmentation of the supra‐molecular ionic assemblies detected in CSI‐MS are performed using the in‐source collision‐induced dissociation experiments. The experimental measurements in CSI‐MS, interpreted at the light of the molecular modelization results, suggest that the insertion of urea in adducts of chlorides with cholinium cations does not lead to the most stable ions.

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“…CSI MS used it to analyze reline, i.e., Choline chloride: urea (1:2, mol/mol). [26] The ions detected on the CSI MS were distinctive of Choline Chloride salt and Urea association into a chloride adduct. It was found that an increase in the number of urea molecules does not imply a stabilization of the NaDES.…”

“…Indeed, classical assay based on colorimetric measurement could be disturbed by the NaDES component leading to intensive research of alternative processes. For example, the direct electrochemistry of nine phenolic compounds was investigated for the first time in three DES-based media by cyclic voltammetry and differential pulse voltammetry in comparison with the Folin-Ciocalteu assay by Percevault et al [26]. The Folin-Ciocalteu test is routinely employed for determining the total phenolic content in extracts; even though it is widely used in DES extracts [47], sometimes it can be difficult to handle or even inaccurate in some (Na)DES, while electrochemical techniques are quick, simple and do not require the use of metals or organic reagents.…”

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“…This led to a supramolecular network made by the association of one cholinium chloride salt and two urea molecules. 27,[29][30][31][32]…”

“…[21][22][23][24][25][26] Their organization can be described through non-covalent molecular networks associating a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD). [27][28][29][30][31][32] Examples of DES applications in chemistry were described through extraction and microextraction techniques, [33][34][35][36] electrochemistry, 37 and catalysis. 38,39 Several studies have also shown that DESs based on choline chloride were able to absorb air contaminants such as sulfur dioxide 40,41 or ammonia.…”