It is essential to understand the interaction between the analyte, mobile phase and the column chemistry for the best possible separation of molecules. Of all three, the mobile phase in HPLC is the easiest to modify and thus, usually contains different eluent additives or buffers. While using mass spectrometry undoubtedly increases the variety of analytes possible to detect, it also introduces limiting factors such as the requirement of the volatility of the eluent. Most common additives in LC-MS systems are formic and acetic acid, their ammonium salts as well as ammonium bicarbonate. In our recent paper, we have proposed novel – fluorinated, eluent additives (hexafluoroisopropanol, hexafluoro-tert-butyl alcohol, trifluoroethanol as well as nonafluoro-tert-butyl alcohol and perfluoropinacol). Their influence was shown on rather simple exemplary molecules, which are widely spread over different logP values, containing protonated and deprotonated acids and bases. All novel fluorinated eluent additives demonstrated a strong influence on basic polar analytes in basic medium – they drastically increased retention. A decrease in retention was observed for acidic analytes when these novel eluent additives were used.
Moreover, current research displays a comprehensive overview of retention mechanisms for nonafluoro-tert-butyl alcohol and is the first time ever when perfluoropinacol has been introduced as eluent additive for reversed phase chromatography. Additionally, the influence on MS signal was studied when fluoroalcohols were used as eluent additives. This is also the first time when the absolute pH (pHabs) scale was used for expressing the mobile phase pH.
Current fundamental research forms a basis for a better understanding of the influence of fluoroalcohols as eluent additives and will help in the assay development in a wide range of applications.
This work is part of a larger endeavor – to promote a wider usage the unified pH scale (pHabs) by the research and technology communities, which is currently in progress via the UnipHied.
The UnipHied project is funded from the EMPIR programme (project 17FUN09) co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.