A new hydrophobic support material, Porous Graphitic (or Graphitised) Carbon (PGC) has been studied using both Liquid (LC) and Gas Chromatography (GC). The heat of adsorbtion (AH) of typical LC solvents determined on PGC, using GC, showed that AH increased with the molecular area (Ax) of solvents for well graphitised carbons, but that AH/Ax values were similar for all solvents studied. By definition, AH/Ax is a measure of eluotropic strength. The results reveal that a strong eluotropic series does not exist on carbon. A strong eluotropic series does exist on silica. In this case, AH/Ax values of solvents were dependent upon their eluotropic strengths (Eo), determined by LC. GC work was carried out using alcohols, ketones and aliphatic hydrocarbons on PGC, modified with different amounts of Carbowax 1500. Symmetrical peaks were obtained with coated materials. The column efficiency (N), first increased and then dropped with increasing Carbowax content on the PGC surface. The retention of ketones and hydrocarbons decreased with increasing amount of Carbowax on PGC. In the case of alcohols, the retention decreased with the initial introduction of Carbowax on to PGC. Some alcohols displayed enhanced retention at 0.10% of Carbowax. All alcohols showed increased retention at the monolayer coverage of Carbowax. In the quest for a perfect material for adsorption GC, PGC samples were hydrogen treated at elevated temperatures (230-1030°C). All hydrogen treated samples failed to display signficantly improved chromatographic properties. PGC was then treated with toluene in a stream of either hydrogen (at 630°C) or nitrogen (at 630°C or 300°C) to eliminate any active sites present on the surface. Hexane was used us an alternative to toluene at 630°C in a stream of hydrogen. Such surface treatments yielded improved materials for adsorption GC. On heating the columns (beyond 230"C), containing these materials, with carrier gas running through the columns, the Chromatography deteriorated in the cases of toluene-treated PGC whilst the Chromatography of the hexane-treatcd PGC remained unaffected. LC work on some aromatic compounds using PGC, coated with surfactants such as Tween 80 or Span 80 showed that, analyte retention decreased with increasing surfactant concentration (up to 0.03% of Tween and 0.02% of Span) in the eluent. N dropped with the introduction of Tween to the PGC. Increasing the ratio of water to mcthanol in the eluent, at a constant eluent concentration of surfactant, resulted in diminishing N, increasing eluent polarity and analyte retention values. Ion pairing was carried out on PGC using cetyltrimethylammonium-bromide (CTAB) as the ion pairing agent, at an eluent pH of 12.5. The retention of solutes, that ionise under these conditions, increased whereas the retention of analytes, that do not ionise, decreased with increasing eluent concentration of CTAB. The coated or chemically modified PGC surfaces are useful in GC whilst the dynamically coated PGC surfaces are important in LC. Such surface treatments can alter the following properties of PGC; (a) Retention characteristics, (b) the selectivity and (c) chromatographic efficiency.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:649514 |
| Date | January 1990 |
| Creators | Dias, H. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13643 |
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