Electrochemically-Induced Reactions of Hexafluorophosphate Anions with Water in Negative Ion Electrospray Mass Spectrometry of Undiluted Ionic Liquids
- West Virginia University, Department of Chemistry (United States)
The influence of water on the observed gas-phase population of negative ions in electrospray mass spectrometry was studied for the undiluted ionic liquid 1,3-butyl-methyl-imidazolium hexafluorophosphate (BMIM{sup +}PF{sub 6}{sup −}). During the electrospray process, electrolytic reduction of water enhances the production of tetrafluorophosphate (F{sub 4}PO{sup −}), which undergoes further reactions to produce difluorophosphate (F{sub 2}PO{sub 2}{sup −}) anions. These anions are observed in addition to the pre-existing hexafluorophosphate anion. The apparent substitution of two fluorine atoms with one oxygen is attributed to a series of reactions initiated by hydrolysis of hexafluorophosphate. This hydrolysis reaction was enhanced by the addition of hydroxide, formed via the hydrolysis of water or through the addition of ammonium hydroxide. The formation of F{sub x}PO{sub y}{sup −} was studied as a function of the electrospray current and solution flow rate. The mass spectral response shows a quantitative logarithmic relationship between ΣF{sub x}PO{sub y}{sup −} signal intensities (adjusted for mole equivalents of H{sub 2}O required) and the amount of water present, against which the water content could be rapidly assessed. Results were found to be comparable to Karl Fischer titration data.
- OSTI ID:
- 22774039
- Journal Information:
- Journal of the American Society for Mass Spectrometry, Vol. 17, Issue 7; Other Information: Copyright (c) 2006 American Society for Mass Spectrometry; Country of input: International Atomic Energy Agency (IAEA); ISSN 1044-0305
- Country of Publication:
- United States
- Language:
- English
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