As a follow up to the Analytix Reporter Issue 10 article, “Applications Employing New 2.7 μm Porous Graphitic Carbon Particles for U/HPLC”, we explore here, in a shortened review from Issue 13, the more fundamental and theoretical topics concerning PGC materials. What are they and how do they work as a stationary phase material in HPLC?
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Despite its uniqueness compared to more conventional liquid chromatography (LC) stationary phases, Porous Graphitic Carbon (PGC) has been around since the 1980’s. During that time, the goal was to generate a material that had the advantages of standard Reversed- Phase (RP) phases based on silica supports while eliminating some of the negative attributes, such as limited pH range, limited temperature stability, and secondary interactions from active surface silanols. What the researchers discovered was while there is some overlap with standard RP phases, some degree of graphitization gives the material other distinctive properties. Due to some of these characteristics specific to graphites, PGC has situated itself as more of a specialty phase for more challenging separations when other more traditional options do not work.
The article explores the background and science behind PGC looking at the following areas:
- Particle morphology
- Retention properties
- Interaction with hydrophobic analytes
- Interaction with hydrophilic analytes
- The importance of analyte stereochemistry
It concludes that PGC is a unique stationary phase giving the chromatographer an additional chemistry option to separate challenging compounds beyond the realm of conventional reversed-phase chromatography. In many respects, the PGC column may behave like a reversed-phase column with enhanced temperature, and pH stability, but due to the special properties of graphite, polar compounds that may need HILIC or ion-exchange conditions can be retained as well. However, some aspects of the analyte’s stereochemistry and potential surface area contact points need to be considered for there to be enough retention. Although the mechanisms are not fully understood, especially in regards to PREG, it is undeniable that PGC has unique retention properties towards polar compounds – especially planar molecules or analytes with double bond conjugation that can interact with the electron cloud of graphite. More research into these fundamental mechanisms will yield more accurate retention prediction models.