They may be called PFP, PFPP, pentafluorophenyl, fluorophenyl or F5 phases. What they all have in common is the structure shown above (the pentafluorophenyl group) attached to the silica particles.
Most modern phases contain a propyl spacer between the above group and the silica, so that the phase looks something like this:
A “PFPP” phase refers to the above structure with the propyl spacer. However, quite often the other names apply as well, depending on the column and vendor. We are quite proud to offer our new PFPP phases, the Raptor Fluorophenyl and the Force Fluorophenyl, which are designed using the latest advances in bonding technology. The following are some questions that may come to mind.
What makes the phase useful?
Due to the presence of the fluorine atoms, a fairly polar phase is created that allows for HILIC separations. The electronegativity of the fluorine atoms, in combination with the delocalized electrons from the aromatic ring, result in increased retention for charged bases (like amine compounds) and other electronegative compounds (those containing halogen atoms, O, or N). Also, due to the presence of the aromatic ring and propyl spacer, the phase still retains some nonpolar characteristics, so it can also be used in reverse phase mode.
I recommend the following if you wish to read more about HILIC separations and characteristics of PFPP phases:
Restek USLC, Ultra Selective Liquid Chromatography
Reliable HILIC LC-MS/MS Analysis of 4-Methylimidazole (4-MEI) on Raptor FluoroPhenyl Columns
How should these phases be used?
For HILIC mode, use a mobile phase that is at least 50% organic solvent. If using a gradient, start with high organic and program up to high aqueous content. Often a mild modifier, such as 0.1% formic acid is used in both mobile phase A and B. Here are some examples:
For reverse phase mode, conditions similar to what is used with C18 are common, except that sometimes the gradient starts with a higher organic content to encourage retention of highly polar compounds, perhaps 30% organic or higher. Here are some examples:
How do I condition this phase before using?
Equilibration times will vary according to application. If using for the first time or after changing solvents in your mobile phase(s), it may take as much as 50 column volumes or more. It is recommended to always start with a new column when developing methods, as the phase is sometimes permanently altered by certain mobile phase modifiers and buffer salts.
How do I prepare my sample to use with this phase?
Samples should be as clean as possible, as the phase is somewhat sensitive to differences in sample matrix. If sample matrix is an issue that does not lend itself well to cleanup, it is best to quantitate using matrix-matched calibration standards. As with any LC column, particulates should be removed by filtration prior to loading on the instrument.
I hope this has helped to answer some of the questions you might have about using PFP phases.
Thank you for reading.