Development and use of carbon adsorbents in high-performance liquid-solid chromatography

Principles and applications of porous graphitic carbon stationary phase in liquid chromatography: An update

The introduction of carbon black particles as packaging material for liquid chromatography columns dates back to the late 70's, in an attempt to overcome common drawbacks associated with silica-based packings. The latter consisted of the difficulty in eliminating or shielding the polar residual silanol groups, responsible for secondary interactions with non-polar ligands, but also the fragility and instability of the bonded ligands. Since then, numerous advances have been made in the synthesis of carbon-based stationary phases, achieving excellent objectives in terms of chromatographic performance and versatility, mainly related to the possibility of working under a wide range of pH (1-14) and temperature (higher than 200 °C). The purpose of this review is to summarize the most significant advances in the synthesis and application of the porous graphitic carbon phase (PGC), in the last decade. Literature reports based on the use of PGC columns are focused on the analysis of a wide range of chemicals, spanning from polar compounds to apolar polymers. More in detail, polar analytes have included both small molecules and larger biomolecules (such as oligo- and polysaccharides, peptides, and glycopeptides), with special emphasis on additional selectivity for isomer separation. On the other hand, applications devoted to the analysis of non-polar analytes could benefit from the use of high temperatures, allowing for the achievement of satisfactory separations within reduced analysis time.

Application of Carbonaceous Materials in Separation Science

Porous carbons in the separation sciences occupy an important niche owing to their unique retention characteristics, chemical stability and the ability to control pore structure through template strategies. However, these same synthetic processes utilise oil-based carbonising resins and high temperature, energy-intensive pyrolysis steps to ensure the carbon product has pore-size regularity, minimal micropore content and homogeneous surface chemistry. This chapter will primarily focus on the development of porous carbons for application as chromatographic stationary phases. Discussion will cover the unique characteristics of the porous carbon retention mechanism and its application in separating a broad range of analyte classes. The chapter then moves on to describe the current disadvantages in the manufacture of commercially available carbon phase and then highlight recent efforts aimed at the development of alternative porous carbon stationary phases derived from sustainable carbon precursors.

A microfabricated graphitic carbon column for high performance liquid chromatography

We report the first development of a novel, planar, microfluidic, graphitic carbon separations column utilizing an array of graphitic micropillars of diamond cross-section as the chromatographic stationary phase. 795 nm femtosecond laser ablation was employed to subtractively machine fluidic architectures and a micropillared array in a planar, graphitic substrate as a monolithic structure. A sample injector was integrated on-chip, together with fluid-flow distribution architectures to minimize band-broadening and ensure sample equi-distribution across the micro-pillared column width. The separations chip was interfaced directly to the ESI probe of a Thermofisher Surveyor mass spectrometer, enabling the detection of test-mixture analytes following their differential retention on the micro-pillared graphitic column, thus demonstrating the exciting potential of this novel separations format. Importantly, unlike porous, graphitic microspheres, the temperature and pressure resilience of the microfluidic device potentially enables use in subcritical H(2)O chromatography.

Preparation and evaluation of carbon coated alumina as a high surface area packing material for high performance liquid chromatography

The retention of polar compounds, the separation of structural isomers and thermal stability make carbonaceous materials very attractive stationary phases for liquid chromatography (LC). Carbon clad zirconia (C/ZrO(2)), one of the most interesting, exhibits unparalleled chemical and thermal stability, but its characteristically low surface area (20-30 m(2)/g) limits broader application as a second dimension separation in two-dimensional liquid chromatography (2DLC) where high retentivity and therefore high stationary phase surface area are required. In this work, we used a high surface area commercial HPLC alumina (153 m(2)/g) as a support material to develop a carbon phase by chemical vapor deposition (CVD) at elevated temperature using hexane vapor as the carbon source. The loading of carbon was varied by changing the CVD time and temperature, and the carbon coated alumina (C/Al(2)O(3)) was characterized both physically and chromatographically. The resulting carbon phases behaved as a reversed phase similar to C/ZrO(2). At all carbon loadings, C/Al(2)O(3) closely matched the unique chromatographic selectivity of carbon phases, and as expected the retentivity was increased over C/ZrO(2). Excess carbon - the amount equivalent to 5 monolayers--was required to fully cover the oxide support in C/Al(2)O(3), but this was less excess than needed with C/ZrO(2). Plate counts were 60,000-76,000/m for 5 μm particles. Spectroscopic studies (XPS and FT-IR) were also conducted; they showed that the two materials were chemically very similar.

Retention characteristics of polybutadiene-coated zirconia and comparison to conventional bonded phases

This paper presents a detailed study of retention on a reversed-phase material made by coating polybutadiene (PBD) on porous zirconia. PBD-coated zirconia particles with six different carbon loads (0.25-5.6% carbon by weight) were prepared by evaporatively depositing and cross-linking PBD on microparticulate porous zirconia. Retention data of a homologous series of alkylbenzenes were obtained on the six PBD phases as a function of mobile phase composition in methanol-water and acetonitrile-water mixtures from 20 to 50% (v/v). The results obtained for the phase were compared to those for conventional octadecylsilane (ODS) bonded phases, and the effect of the amount of PBD on retention was studied in detail. We find that, per amount of bonded phase, the PBD phase is less retentive than is the ODS phase, but it has comparable hydrophobic selectivity. Furthermore, the PBD phase has about the same sensitivity toward changes in mobile phase composition as does the ODS phase, and its solute shape selectivity is similar to that of a monomeric ODS phase. Finally, we conclude that retention arises primarily from a partition-like process.