Selective Separation of Polar Unsaturated Organics Using a Water Stationary Phase in Gas Chromatography
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2022-04
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Abstract
In this thesis, a water stationary phase is explored as a novel means of selectively separating unsaturated analytes in gas chromatography. Several unsaturated/saturated analyte pairs consisting mainly of alcohols and carboxylic acids were examined using both a 30 m conventional non-polar HP-5 column and an 11 m water phase column. For most investigated on the HP-5 column, analytes often eluted very close to each other (~6-12 seconds apart) with poor resolution. By comparison, the shorter water phase column well separated each of the analogue pairs by about 3-8 minutes or more. As well on the water phase, analytes with a triple bond were much more retained than those with two double bonds, which in turn were much more retained than those with one double bond. Conversely, on the HP-5 column these were poorly separated if at all.
Next, the addition of various metal ion salts to the water phase was explored. While Ca2+ ion produced modest increases in selectivity, the addition of Ag+ ion was most influential and further increased the original water phase selectivity by a factor of 2.3. This also illustrated the flexibility of the system to be adjusted for such separations as a variety of metal ion salts could be easily dissolved into the water stationary phase for this investigation. Lastly, an exploration of unsaturated analyte separations found that cis/trans isomers were baseline resolved on the water phase but co-eluted on a 30 m conventional polar Carbowax column. Similarly, positional isomers varying the location of the double bond were found to separate with a selectivity value near 1.1 on the Carbowax column, whereas on the water phase column they yielded a value of 1.3 and eluted in the reverse order. The mechanistic implications of OH---pi bonding in the water phase was discussed as a potential origin for the selectivity observed. The method was applied to gasoline, model contaminated water, essential oil, and food stuff analysis. Results indicate that this method could be a very useful means of selectively separating such unsaturated analytes.
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Marno Jones, A. (2022). Selective separation of polar unsaturated organics using a water stationary phase in gas chromatography (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.