Post-Chromatographic Dicationic Ionic Liquid-Based Charge Complexation for Highly Sensitive Analysis of Anionic Compounds by Ultra-High-Performance Supercritical Fluid Chromatography Coupled with Electrospray Ionization Mass Spectrometry

Abstract

A green analytical strategy has been developed for the analysis of 10 perfluorinated compounds (PFCs) incorporating supramolecular solvent (SUPRAS)-based extraction and ultra-high-performance supercritical fluid chromatography (UHPSFC)–tandem mass spectrometry. The SUPRAS was prepared through self-assembly of reverse micelles by mixing heptanol, tetrahydrofuran, and water at optimized volume ratios. An imidazolium-based germinal dicationic ionic liquid (DIL), 1,1-bis­(3-methylimidazolium-1-yl) butylene difluoride ([C4(MIM)2]­F2), was dissolved in the make-up solvent of UHPSFC and introduced post-column but before the electrospray ionization source. After chromatographic separation on a Torus DIOL analytical column (100 mm × 2.1 mm, 1.7 μm), the PFC analytes associated with the DIL reagent through charge complexation. The formation of positively charged complexes resulted in improved ionization efficiency and analytical sensitivity. Enhancement in signal intensity by one to two magnitudes was achieved in the positive ionization mode compared to the negative ionization mode without using the dicationic ion-pairing reagent. The developed protocol was applied to 32 samples of real textiles and 6 samples of real food packaging materials, which exhibited great potential for the analysis of anionic compounds.

Analysis of needs for enforcement of PFAS in articles and chemical products

“…A novel green analytical strategy (in this context, "green" means using less solvents), characterized by the use of fewer solvents, has been pioneered by Li et al (2021) for the analysis of 10 per luorinated compounds (PFAS). This approach incorporates supramolecular solvent (SUPRAS)-based extraction and ultra-high performance supercritical luid chromatography (UHPSFC)-tandem mass spectrometry.…”

“…The typical LOQs ranged between 0.2 and 3.2 µg/kg for the SUPRAS-based extraction system coupled with SFC. However, the utilization of the SUPRAS-based extraction with SFC is not a commonly employed routine methodology, and its integration into commercial laboratories may pose a challenge (Li et al, 2021).…”

Enhancing sensitivity in miniature mass spectrometry analysis via dicationic ionic liquid-based matrix-assisted ionization and charge inversion reactions

“…17,18 Dicationic ionic liquids (DILs), an innovative group of ILs, consist of a dication paired with two anions. DILs have been used as complexing agents in analytical methods based on high-performance liquid chromatography (HPLC), 19,20 supercritical fluid chromatography (SFC), 21 ion chromatography (IC), 22 or capillary electrophoresis (CE) 23 followed by MS detection. During electrospray ionization (ESI), corona discharge is more prevalent in negative ion mode, which may cause arcing events.…”

“…These adducts can be detected in positive ion mode with greatly enhanced sensitivity. 26 This charge inversion reaction has been applied in the analysis of bisphosphonate drugs, 27 sphingolipids, 28 herbicides, 29 long-chain unsaturated fatty acids, 30 fatty acid methyl esters, 31 per-and polyfluoroalkyl substances (PFAS), 21 nucleotides, 32 and various other compounds. 33,34 This strategy exhibits major advantages, such as enhanced spray stability and analysis sensitivity.…”

Electromembrane Extraction and Dual-Channel Nanoelectrospray Ionization Coupled with a Miniature Mass Spectrometer: Incorporation of a Dicationic Ionic Liquid-Induced Charge Inversion Strategy

“…However, corona discharge is more prevalent in the negative-ion mode as opposed to the positive-ion mode, resulting in reduced spray stability and increased background noise. − To address this limitation, a charge inversion reaction can be initiated by introducing an ion-pairing reagent during the electrospray process to reverse the ion charge polarity of anionic analytes on demand with the aims of increasing ionization efficiency and selectivity . Dicationic ionic liquids (DILs), consisting of a dication paired with two counter-anions, have been used as postcolumn ion-pairing reagents for analytical methods based on HPLC, , supercritical fluid chromatography (SFC), IC, , or CE , followed by MS detection. The presence of DILs allows the formation of overall positively charged complexes for the analysis of anionic analytes, which would circumvent the use of the less preferable negative-ion mode.…”