Utility of Postcolumn Addition of 2-(2-Methoxyethoxy)ethanol, a Signal-Enhancing Modifier, for Metabolite Screening with Liquid Chromatography and Negative Ion Electrospray Ionization Mass Spectrometry

Abstract

A strategy for highly sensitive metabolite screening by liquid chromatography-electrospray ionization (ESI) mass spectrometry with the negative-ion mode that involves the use of a reversed-phase column in gradient-elution mode and postcolumn addition of 2-(2-methoxyethoxy)ethanol (2-MEE), a novel signal-enhancing modifier, has been described. When a mobile phase of 50 mM ammonium acetate/acetic acid buffer (pH 4.4) at a flow rate of 100 microL/min was employed, poor ESI response of ibuprofen as a model drug, probably due to both the high surface tension of the mobile phase and the ion-suppression effect of acetate anion in the mobile phase, was observed. On the other hand, the postcolumn addition of 2-MEE (50 microL/min) into the mobile phase counteracted the ion suppression as well as the surface tension problem, resulting in approximately 100-fold signal enhancement of the analyte. The metabolite screening of ibuprofen in human urine was subsequently carried out comparing the results with and without postcolumn addition of 2-MEE. The results indicated that the postcolumn addition of 2-MEE dramatically improved the ESI responses of all urinary metabolites detected without affecting the chromatographic separation.

Sensitivity enhancement in liquid chromatography/atmospheric pressure ionization mass spectrometry using derivatization and mobile phase additives

“…The poor ionization efficiency may have been due to both the high surface tension of the mobile phase and the ion-suppression effect of the acetate anion in the mobile phase. Post column addition of 2-(2-methoxyethoxy)ethanol (50 L/min) increased the signal of analyte approximately 100-fold [99] and dramatically improved the ESI responses of all urinary metabolites as well. This method was also used to enhance the signal of rat urinary and biliary metabolites for a novel antirheumatic drug esonarimod [100].…”

Buffer Loading for Counteracting Metal Salt-Induced Signal Suppression in Electrospray Ionization

“…32 Similarly, Yamaguchi et al reported a 100-fold improvement in sensitivity for ions formed from solutions containing ammonium acetate and acetic acid, by addition of the low vapor pressure solvent 2-(2-methoxyethoxy)ethanol (2-MEE; bp 193 °C). 33 The authors speculated that "the ion-suppression effect of acetate ion" is responsible in part for the poor ESI response obtained from ammonium acetate/acetic acid-containing solutions and that 2-MEE counteracts signal suppression by allowing acetic acid and water to preferentially evaporate from the electrospray droplets prior to ion formation. 33 Here, we report that both the abundance and the reproducibility of ion signal of cytochrome c and ubiquitin ions formed by nanoES from aqueous solutions containing 0 or 2.0 × 10 −2 M sodium chloride are significantly improved by adding 7 or 8 M ammonium acetate to electrospray solutions.…”

“…33 The authors speculated that "the ion-suppression effect of acetate ion" is responsible in part for the poor ESI response obtained from ammonium acetate/acetic acid-containing solutions and that 2-MEE counteracts signal suppression by allowing acetic acid and water to preferentially evaporate from the electrospray droplets prior to ion formation. 33 Here, we report that both the abundance and the reproducibility of ion signal of cytochrome c and ubiquitin ions formed by nanoES from aqueous solutions containing 0 or 2.0 × 10 −2 M sodium chloride are significantly improved by adding 7 or 8 M ammonium acetate to electrospray solutions. We propose that this effect is due to the removal of Na + and Cl − from solution by precipitation within the evaporating electrospray droplets prior to the formation of gas-phase protein ions.…”

Analysis of sulfonated compounds by reversed-phase ion-pair chromatography—Mass spectrometry with on-line removal of non-volatile tetrabutyl ammonium ion-pairing agents

“…In addition, as a typical feature of the negative ion detection mode, only a low background occurred and therefore, excellent and easily interpretable mass spectra were obtained with both, ESI and APCI. As a typical example of a sulfonated aromatic compound, Figure 7 shows the APCI mass spectrum of Crocein Orange G. It is worth mentioning that post-column addition of 2-(2-methoxyethoxy)ethanol proved to exert a beneficial influence on signal intensities, as first published by Yamaguchi et al [24].…”