This article from Issue 10 of the Analytix Reporter, produced by Merck, describes a unique stationary phase for improved retention and analysis of polar compounds and examples of its applications in food and clinical analysis.
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Introduction
Since the 1960s, the scientific discipline of high-performance liquid chromatography (HPLC) has been dominated by silica particle-based column technologies. From irregular silica gels of the 1960s and 1970s to present-day superficially porous particles (SPPs), sub-2 µm fully porous particles (FPPs), and silica-based monoliths, the scientific literature is teeming with information on the applications of silica particle packed columns for a wide range of analyte polarities. Although there are advantages and disadvantages to each of these different particle modalities, in general, all silica-based packings have three common flaws: (1) a limited pH range for bonded phase stability (2) a limited temperature range for bonded phase stability, and (3) secondary interactions from active, silanol species (though, this can be a benefit when needed to elicit resolution by ionic interactions).
Back in the early days of chromatography, liquid chromatography (LC) utilized carbon particles. However, due to the nonlinear adsorption isotherms produced by then available, active carbon particles, they were not regarded as suitable for HPLC applications. Through the late 1970s and 1980s, researchers optimized porous graphitic carbon (PGC) particles for less active surfaces, leading to the commercialization of carbon particle packed HPLC. The following years saw optimization of synthetic procedures to bring down the particle size from 10 µm to 3 µm, yielding higher efficiencies in the resolution of analytes. Finally, a breakthrough, novel, synthetic process was developed over the last two years to create a smaller (2.7 µm) carbon particle with a narrower particle size distribution (PSD), higher mechanical stability, and reproducibility — resulting in improved efficiencies in the separation of challenging analytes.
Download the full article for more information and to view examples of the applications below:
- Analysis of Highly Polar Pesticides
- Analysis of Paraquat and Diquat - Converting an Existing HILIC Method to a PGC Method with a Simpler Gradient
- Separation of Vitamin D2 and D3 Metabolites and Their Epimers
Summary
Porous graphitic carbon is a novel stationary phase and gives the chromatographer an additional chemistry option in the separation of challenging compounds, beyond the realm of conventional silica-based reversed-phase chromatography. While in many respects, PGC may behave like a reversed-phase column, it also offers the advantages of enhanced temperature, solvent, and pH stability. Moreover, because of the unique properties of graphite, highly polar compounds (that may need HILIC or ion-exchange conditions) can be retained on a PGC column. Although its retention mechanisms are yet to be elucidated, it is clear that PGC has unique retentive properties towards polar compounds – especially planar molecules or analytes with double bond conjugation that can interact with the electron cloud of graphite. PGC is a unique stationary phase amongst more conventional HPLC stationary phases and further advancements in PGC particle design may result in even better resolving power for a wider range of compounds.
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