Effect of mobile phase on electrospray ionization efficiency

Abstract : Electrospray (ESI) ionization efficiencies (IE) of a set of 10 compounds differing by chemical nature, extent of ionization in solution (basicity), and by hydrophobicity (tetrapropylammonium and tetraethylammonium ion, triethylamine, 1-naphthylamine, N,N-dimethylaniline, diphenylphthalate, dimethylphtahalate, piperidine, pyrrolidine, pyridine) have been measured in seven mobile phases (three acetonitrile percentages 20%, 50%, and 80%, and three different pH-adjusting additives, 0.1% formic acid, 1 mM ammonia, pH 5.0 buffer combination) using the relative measurement method. MS parameters were optimized separately for each ion. The resulting relative IE data were converted into comparable logIE values by anchoring them to the logIE of tetrapropylammonium ion taking into account the differences of ionization in different solvents and thereby making the logIE values of the compounds comparable across solvents. The following conclusions were made from analysis of the data. The compounds with pK(a) values in the range of the solution pH values displayed higher IE at lower pH. The sensitivity of IE towards pH depends on hydrophobicity being very strong with pyridine, weaker with N,N-dimethylaniline, and weakest with 1-naphthylamine. IEs of tetraalkylammonium ions and triethylamine were expectedly insensitive towards solution pH. Surprisingly high IEs of phthalate esters were observed. The differences in solutions with different acetonitrile content and similar pH were smaller compared with the pH effects. These results highlight the importance of hydrophobicity in electrospray and demonstrate that high hydrophobicity can sometimes successfully compensate for low basicity.
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Article dans une revue
Journal of The American Society for Mass Spectrometry, Springer Verlag (Germany), 2014, 25 (11), pp.1853-1861. 〈10.1007/s13361-014-0969-x〉
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https://hal.archives-ouvertes.fr/hal-01230362
Contributeur : Agnès Bussy <>
Soumis le : mercredi 18 novembre 2015 - 11:29:13
Dernière modification le : jeudi 29 novembre 2018 - 11:52:06

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Jaanus Liigand, Anneli Kruve, Ivo Leito, Marion Girod, Rodolphe Antoine. Effect of mobile phase on electrospray ionization efficiency. Journal of The American Society for Mass Spectrometry, Springer Verlag (Germany), 2014, 25 (11), pp.1853-1861. 〈10.1007/s13361-014-0969-x〉. 〈hal-01230362〉

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