Study on the formation of an amoxicillin adduct with methanol using electrospray ion trap tandem mass spectrometry

Abstract

The possibility of using the protonated methanol-adduct of antimicrobial amoxicillin for its identification and quantification at residue levels has been investigated, since it is impossible to completely suppress the formation of these adducts when methanol is present in the solvent system. This process has been monitored over time and as a function of concentration. It was determined that adducts were instantly formed and that the abundance of the protonated methanol-adduct at m/z 398 increased at the expense of the protonated molecule m/z 366 with storage time. The effect of several common solvents and mobile-phase additives on the ionization efficiency of amoxicillin and the formation of the methanol adduct has also been investigated. It was shown that the mass spectra of amoxicillin were strongly influenced by the solvent in which the analyte is dissolved and by the analyte concentration, as well as by the composition of mobile phase. Methanol was determined to be the best spray solvent, as it provided spectra with the lowest abundance of dimer ions. It was also determined that acetic acid as the mobile-phase additive provided the highest signal intensities, while ammonium acetate should not be used as an additive for the determination of amoxicillin at residue levels. Using high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS), fragmentation of the protonated molecules and the protonated methanol-adduct ions, in both positive and negative ion mode, has been performed. The fragmentation was stable and strong product ion spectra were obtained. The linearity of the MS detector response, and that of the chromatographic method, was tested. Due to the linear behaviour it was concluded that the protonated methanol-adduct ion can be used for analytical purposes, i.e. for identification and quantification of amoxicillin at trace levels.

Behavior of amoxicillin in wastewater and river water: identification of its main transformation products by liquid chromatography/electrospray quadrupole time‐of‐flight mass spectrometry

“…Low recoveries for AMX were obtained (35 ± 9%, n = 3). Similarly to the other TPs, we used accurate tandem mass spectrometry to structurally elucidate the compound amoxicilloic acid methyl ester (AMXC‐Me) 31–33. It was evidenced that in the elution step appreciable amounts of AMXC‐Me (ion formula C 17 H 23 N 3 O 6 S, m/z 398.1378; 0.50 ppm mass error) were formed (see Table 1).…”

Systematic LC‐MS/MS bioanalytical method development that incorporates plasma phospholipids risk avoidance, usage of incurred sample and well thought‐out chromatography

“…For certain analytes, perfl uorinated phases have been shown to exhibit not only RP characteristics but also normal-phase-like characteristics, especially in a mobile phase of high organic percentage. In LC-MS/MS bioanalysis, the selection of columns and mobile phases is further complicated since a mobile phase could significantly aff ect the nature and intensity of the analyte mass spectrometric response obtained using the same column (Jemal, 2000;Jemal and Xia, 2006;Delatour and Leclercq, 2005;Xia et al, 2006b;Patring and Jastrebova, 2007;Grujic et al, 2008;Peng and Farkas, 2008). Although not as widely reported, there have also been reports of observations that the type/brand of the column used could aff ect the analyte response using the same mobile phase (Xia et al, 2006b;Piovan et al, 2004;Ouyang et al, 2005).…”

New covalent modifications of phosphatidylethanolamine by alkanals: mass spectrometry based structural characterization and biological effects

“…Taking into account the molecular weight of hexanal of 100.087 g/mol (monoisotopic mass) and the elemental composition calculated from high resolution MS scans, we propose formation of monomeric, dimeric and trimeric Schiff base adducts, and their hydrated forms on PE head group (Scheme 1) and the ion at m/z 790.60 was assigned as amide-linked type adduct between hexanal and the amino group of PE. Additionally, the ion at m/z 906.72 was proposed to represent a methanol adduct [M + CH 3 OH] + [38][39][40] of the ion 874.69. In order to confirm the proposed Schiff base adducts, reduction with NaCNBH 4 was performed.…”