Ascorbic acid for homogenous redox buffering in electrospray ionization–mass spectrometry

Abstract

Electrospray ionization (ESI) involves the dispersion of a liquid containing analytes of interest into a fine aerosol by applying a high potential difference to the sample solution with respect to a counter electrode. Thus, from the electrochemical point of view, the ESI source represents a two-electrode controlled-current electrochemical flow cell. The electroactive compounds part of the solvent sprayed may be altered by occurring electrolysis (oxidation in positive ion mode and reduction in negative ion mode). These reactions can be troublesome in the context of unknown identification and quantification. In the search for a simple, inexpensive, and efficient way to suppress electrochemical oxidation in positive ESI, the usability of ascorbic acid, hydroquinone, and glutathione for homogenous redox buffering was tested. Performance of the antioxidants was assessed by analyzing pharmaceutical compounds covering a broad range of functional groups prone to oxidation. Different emitter setups were applied for continuous infusion, flow injection, and liquid chromatography/mass spectrometry experiments. Best performance was obtained with ascorbic acid. In comparison to hydroquinone and glutathione, ascorbic acid offered superior antioxidant activity, a relatively inert oxidation product, and hardly any negative effect on the ionization efficiency of analytes. Furthermore, ascorbic acid suppressed the formation of sodiated forms and was able to induce charge state reduction. Only in the very special case of analyzing a compound isobaric to ascorbic acid, interference with the low-abundant [ascorbic acid+H]+ signal may become a point of attention.FigureAscorbic acid efficiently suppresses analyte oxidation and formation of sodiated forms in positive electrospray ionizationElectronic supplementary materialThe online version of this article (doi:10.1007/s00216-012-6196-z) contains supplementary material, which is available to authorized users.

Liquid chromatography-mass spectrometry platform for both small neurotransmitters and neuropeptides in blood, with automatic and robust solid phase extraction

“…Best resolution (R s ) and N were achieved with a mobile phase consisting of 70% ACN and 30% 100 mM ammonium formate at pH 3 (see Supplementary note Mobile phases, for brief discussion on other mobile phases examined). In addition, 300 μM ascorbic acid (anti-oxidant) was added to the mobile phase to avoid online-oxidation effects2021 (see Supplementary note Online oxidation).…”

Photo-initiated copolymerization of allyl and vinyl ethers with dialkyl fumarates: A mechanistic investigation by ESI mass spectrometry

“…Polymerization inhibitors are present in very small amounts in monomers sensitive to free radicals, generally between 100 and 1000 ppm. The relatively high content of the population of oligomers including a hydroquinone fragment may arise from the propensity of this aromatic fragment for oxidation during the ESI process [44]. This phenomenon would enhance the detectability of the corresponding species.…”

Hyphenation of Electrochemistry with Mass Spectrometry for Bioanalytical Studies

“…Therefore, the ESI source can be considered as an electrochemical cell itself [6,8]. In order to prevent unwanted electrochemical reactions in the ESI source, redox buffers can be employed [8]. A cone-shaped mist of charged droplets is emitted from the capillary tip (Taylor cone).…”

“…At atmospheric pressure the solution is infused through the narrow metal capillary which is held at the potential of some kV vs. counter electrode. Therefore, the ESI source can be considered as an electrochemical cell itself [6,8]. In order to prevent unwanted electrochemical reactions in the ESI source, redox buffers can be employed [8].…”