High Pressure Liquid Chromatography (HPLC) is the process of separating multiple analytes by differing affinities toward the stationary phase. The selectivity of a stationary phase is dependent on the surface functional groups, though the majority of research only characterises new phases on a mesoscopic level. Solid-state NMR is a non-invasive technique which can provide detailed analysis on these materials on a molecular level. The technique can be used to determine not only whether a functional group has been successfully incorporated but can analyse whether this group is on the pore surface, able to interact with analytes, or trapped within the pore wall. Furthermore, we can assess whether the organic moiety is homogeneously distributed throughout the stationary phase and the interconnectivity of the silica framework. Analysing new stationary phases on a molecular level is essential to determining their chromatographic applications. The synthesis of three bi-functionalised PMOs under acidic conditions using combinations of bridging (-CH2CHr, -CH=CH-) and tether (-CH2C6HS, -C6Hs) functionalities is presented. By incorporating the organic groups into the silica framework we have produced new reversed phase columns containing a high carbon content. The synthesis of each periodic mesoporous organosilica (PMO) was optimised by varying the acid content and analysing the effect on a mesoscopic scale. The bi- functionalised silicas were then assessed on a molecular level to determine the mobility and the homogeneity of the functionalities using 2-D experiments such as 1H_13C Wideline (WISE) NMR and 1H_29Si Heteronuclear correlation (HETCOR) spectroscopy. The most viable stationary phases were analysed chromatographically using PAH and Tanaka tests and the results were compared to commercially available columns. There are many columns available, though even those containing the same functionality can produce very different separations due to the different synthetic procedures. We have compared two commercially available silicas, 1.7 urn Syncronis (containing monorneric . -C18) and Spherisorb ODS2 (containing polymeric -C18). Although both stationary phases contain the same functionality we have shown that on a molecular level they are very different. We have tried to relate these differences to the selectivity of the two phases. Using techniques such as 1H Nuclear Overhauser Effect Spectroscopy (NOESY) we have been able to compare how a toluene analyte interacts with two -C18 functionalised stationary phases. By also analysing the interactions between a -CH2CHr/ -CH2C6Hs functionalised PMO and toluene we have shown the way in which the analyte interacts with the stationary phase is dependent on the functionality incorporated. The synthesis of a new sphere-in-sphere stationary phase to improve the selectivity of larger biomolecules is presented. By sintering silica nanoparticles to the surface of large pore silica the mechanical strength and surface area of the material is improved though the large pores remaining can still facilitate the mass transfer of high molecular weight compounds. We have shown that by grafting -C12 moieties onto the surface of the silica the shorter elution time of smaller molecules compared to larger compounds is observed, whereas classical size exclusion chromatography (SEC) elutes larger analytes first. This suggests that the separation may be effected by some reversed- phase characteristics.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:569767 |
| Date | January 2011 |
| Creators | Clews, Laura Katherine |
| Publisher | University of Liverpool |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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