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Effect of high performance liquid chromatography mobile phase (methanol versus acetonitrile) on the positive and negative ion electrospray response of a compound that contains both an unsaturated lactone and a methyl sulfone group
Author(s) -
Jemal Mohammed,
Hawthorne Dara J.
Publication year - 1999
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/(sici)1097-0231(19990115)13:1<61::aid-rcm451>3.0.co;2-2
Subject(s) - chemistry , electrospray , formic acid , acetonitrile , adduct , electrospray ionization , ammonium acetate , protonation , methanol , chromatography , mass spectrometry , high performance liquid chromatography , ion , organic chemistry
During method development for the quantitative determination of a compound in human plasma by electrospray high performance liquid chromatography/mass spectrometry (HPLC/MS) we found that the positive ion electrospray response of the compound was dramatically higher (about twentyfold) in a mobile phase that contained methanol rather than acetonitrile. We then decided to investigate the electrospray behavior of the compound under different mobile phase conditions. The positive and negative ion electrospray response of the compound in mobile phases that contained methanol or acetonitrile at neutral and low pH (low pH achieved with formic acid), and with and without ammonium acetate, was investigated. The positive ion response at [M + H] + or [M + NH4] + was consistently higher in a methanolic mobile phase under all conditions studied. The comparatively lower response at [M + H] + or [M + NH4] + in the acetonitrile mobile phase was not due to the formation of adducts or fragment ions not seen in the methanolic mobile phase. However, the negative ion response at [M − H] − or at an adduct of [M − H] − , obtained in a methanolic mobile phase that contained formic acid and/or ammonium acetate was the same as that obtained in the corresponding acetonitrile mobile phase. The positive ion electrospray results obtained for this compound, with an exocyclic α,β‐unsaturated lactone as the only group that can potentially be protonated, are instructive and may serve as an example of the positive electrospray behavior of weakly basic compounds. The negative ion response, attributed to the methyl sulfone group, the only acidic group of the compound, may also serve as an example of the electrospray behavior of weakly acidic compounds. It should be noted that the weakly acidic methyl sulfone group gives good negative ion electrospray response in mobile phases of neutral and acidic pH in which the compound is not expected to be in the ionized form. © 1999 John Wiley & Sons, Ltd.