Retention mechanisms of acidic and basic analytes on the Pentafluorophenyl stationary phase using fluorinated eluent additives

Krit Lossmann; Ruta Hecht; Jaan Saame; Agnes Heering; Ivo Leito; Karin Kipper

doi:10.1016/j.chroma.2022.462850

Retention mechanisms of acidic and basic analytes on the Pentafluorophenyl stationary phase using fluorinated eluent additives

J Chromatogr A. 2022 Mar 15:1666:462850. doi: 10.1016/j.chroma.2022.462850. Epub 2022 Jan 28.

Authors

Krit Lossmann¹, Ruta Hecht¹, Jaan Saame¹, Agnes Heering¹, Ivo Leito¹, Karin Kipper²

Affiliations

¹ University of Tartu, Institute of Chemistry, 14a Ravila Street, 50411 Tartu, Estonia.
² University of Tartu, Institute of Chemistry, 14a Ravila Street, 50411 Tartu, Estonia; Chalfont Centre for Epilepsy, Chesham Lane, Chalfont St Peter, Buckinghamshire, SL9 0RJ, United Kingdom; Department of Clinical and Experimental Epilepsy, Faculty of Brain Sciences, UCL Queen Square Institute of Neurology, Queen Square, London WC1N 3BG, University College London, United Kingdom. Electronic address: karin.kipper@ut.ee.

PMID: 35131517
DOI: 10.1016/j.chroma.2022.462850

Abstract

This work explores the effects of three selected fluoroalcohols - 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), 1,1,1,3,3,3-hexafluorotert‑butyl alcohol (HFTB) and hexafluoro-2,3-(trifluoromethyl)-2,3-butanediol (PP) as novel eluent additives and their effect on the retention of basic and acidic analytes, using a reversed phase (RP) column with a fluorophenyl (PFP) stationary phase. In order to observe the changes in the model analytes' retention, chromatograms were obtained at multiple (5.0; 6.0; 7.0; 8.5; 9.0 and 9.5) pH values depending on the eluent. The retention observed with fluoroalcohols was compared with that of a conventional eluent additive - ammonium acetate. When fluoroalcohols were used as eluent additives, a decrease in the retention factors (compared with ammonium acetate) was generally observed for strong acids. The retention factors of strong bases were generally higher when using HFIP and HFTB as eluent additives. The behaviour of weak bases and weak acids was more nuanced, potentially enabling interesting selectivity. The extent of the effect regarding different fluoroalcohols also varied, with HFIP and HFTB having a more significant effect on the retention of analytes than PP. The retention data were interpreted in terms of the hypothesis that four interactions are at play: (a) hydrophobic retention typical to RP; (b) π-π interactions between the analytes containing an aromatic ring and the aromatic rings on the stationary phase; (c) charge-charge or hydrogen bond interactions between the analytes and partially deprotonated fluoroalcohols adsorbed on the stationary phase and (d) a hydrogen bond or charge-charge interaction between the free silanol groups or their deprotonated forms on the stationary phase and the analytes (either neutral or ionic). Alternative selectivity obtained through fluoroalcohols on the PFP stationary phase was compared with the C18 and biphenyl stationary phases. It was demonstrated that at the same eluent pH but with a different buffer system and/or different RP stationary phases, very different selectivity and retention order can be obtained.

Keywords: HFTB, HFIP; LC-MS; Pentafluorophenyl column; Perfluoropinacol.

MeSH terms

Acids*
Hydrogen-Ion Concentration
Hydrophobic and Hydrophilic Interactions

Substances

Acids