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Effect of Mobile Phase on Electrospray Ionization Efficiency

  • Jaanus Liigand
  • Anneli Kruve
  • Ivo Leito
  • Marion Girod
  • Rodolphe Antoine
Research Article

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.

Graphical Abstract

Key words

ESI Ionization efficiency Solvent effect pH Positive mode Organic phase content 

Notes

Acknowledgment

This work was supported by PUT 34 from Estonian Research Council as well as the institutional funding IUT20-14 (TLOKT14014I) from the Ministry of Education and Research of Estonia, and carried out in part at the High Performance Computing Center of the University of Tartu.

Supplementary material

13361_2014_969_MOESM1_ESM.pdf (464 kb)
ESM 1 (PDF 464 kb)

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Copyright information

© American Society for Mass Spectrometry 2014

Authors and Affiliations

  • Jaanus Liigand
    • 1
  • Anneli Kruve
    • 1
  • Ivo Leito
    • 1
  • Marion Girod
    • 2
    • 3
  • Rodolphe Antoine
    • 2
    • 4
  1. 1.Institute of Chemistry, Faculty of Science and TechnologyUniversity of TartuTartuEstonia
  2. 2.Universite de LyonLyonFrance
  3. 3.CNRS et Universite de Lyon 1, UMR 5280, ISAVilleurbanneFrance
  4. 4.CNRS et Universite de Lyon 1, UMR 5306, ILMVilleurbanne CEDEXFrance

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