title: Sensitivity improvement in hydrophilic interaction chromatography negative mode electrospray ionization mass spectrometry using 2-(2-methoxyethoxy)ethanol as a post-column modifier for non-targeted metabolomics.
abstract: The application of ammonia acetate buffered liquid chromatography (LC) eluents is known to concomitantly lead to ion suppression when electrospray ionization mass spectrometry (ESI-MS) detection is used. In negative ESI mode, post column infusion of 2-(2-methoxyethoxy)ethanol (2-MEE) was shown in the literature to help to compensate this adverse effect occurring in reversed phase liquid chromatography mass spectrometry (RP-LC-MS) analyses. Here a setup of direct infusion and hydrophilic interaction chromatography (HILIC) post-column infusion experiments was established in order to investigate systematically the beneficial effects of 2-MEE. We demonstrate that, 2-MEE can help to improve ESI-MS sensitivity in HILIC too and reveal analyte structure specific behaviors. Our study indicates that 2-MEE especially improves ESI response for small and polar molecules. The ESI response of stable isotope labeled amino acids spiked into biological matrices increases up to 50-fold (i.e. D5-l-glutamic acid) when post column infusion of 2-MEE is applied. A non-targeted analysis of a pooled urine sample via HILIC-ESI-QTOF-MS supports this hypothesis. In direct infusion, the combined application of an ammonia acetate buffered solution together with 2-MEE results in an improved ESI response compared to a non-buffered solution. We observed up to 60-fold increased ESI response of l-lysine. We propose this effect is putatively caused by the formation of smaller ESI droplets and stripping of positive charge from ESI droplets due to evaporation of acetic acid anions. In summary, post-column infusion of 2-MEE especially enhances ESI response of small and polar molecules. Therefore it can be regarded as a valuable add-on in targeted or non-targeted metabolomic HILIC-MS studies since this method sets a focus on this molecule category.
authors.affiliation: Research Unit Analytical BioGeoChemistry, Helmholtz Zentrum München, German Research Center for Environment Health, Neuherberg D-85764, Germany; Chair of Analytical Food Chemistry, Technische Universität München, Freising-Weihenstephan D-85354, Germany; German Center for Diabetes (DZD), Munchen, Germany. Electronic address: Wendelin.Koch@Helmholtz-Muenchen.de.
authors.forename: Wendelin
authors.initials: W
authors.lastname: Koch
authors.affiliation: Research Unit Analytical BioGeoChemistry, Helmholtz Zentrum München, German Research Center for Environment Health, Neuherberg D-85764, Germany; Chair of Analytical Food Chemistry, Technische Universität München, Freising-Weihenstephan D-85354, Germany; German Center for Diabetes (DZD), Munchen, Germany.
authors.forename: Sara
authors.initials: S
authors.lastname: Forcisi
authors.affiliation: Division of Clinical Chemistry and Pathobiochemistry (Central Laboratory), University Hospital Tübingen, 72076 Tübingen, Germany; Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Centre Munich at the University of Tübingen, Tübingen, Germany; German Center for Diabetes (DZD), Munchen, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Lehmann
authors.affiliation: Research Unit Analytical BioGeoChemistry, Helmholtz Zentrum München, German Research Center for Environment Health, Neuherberg D-85764, Germany; Chair of Analytical Food Chemistry, Technische Universität München, Freising-Weihenstephan D-85354, Germany; German Center for Diabetes (DZD), Munchen, Germany. Electronic address: Schmitt-Kopplin@Helmholtz-Muenchen.de.
authors.forename: Philippe
authors.initials: P
authors.lastname: Schmitt-Kopplin
mesh_terms: D055598:Chemical Phenomena; D002851:Chromatography, High Pressure Liquid / Q000295:instrumentation / Q000379:methods*; D000431:Ethanol / Q000031:analogs & derivatives* / Q000737:chemistry; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D055432:Metabolomics; D021241:Spectrometry, Mass, Electrospray Ionization / Q000295:instrumentation / Q000379:methods*
chemical_list: C403469:2-(2-methoxyethoxy)ethanol; D000431:Ethanol
keywords: 2-(2-Methoxyethoxy)ethanol; Dopant; Hydrophilic interaction chromatography; Metabolomics; Time of flight mass spectrometry; Ultra-high pressure liquid chromatography