Library Dissertation Showcase

Injector port acylation of γ-hydroxybutyrate (GHB): condition optimisation, source adjustments, and characterisation of the derivatives

  • Year of Publication:
  • 2020

For several years, GC-MS has been the gold standard to identify γ-hydroxybutyrate (GHB) in seized material and biological samples. However, derivatisation must be carried out first to improve the thermostability of GHB to avoid the production of γ-Butyrolactone (GBL). Various analytical methods have been developed for the analysis of GHB but very few use acylation as a form of derivatisation.
This study aims to fill the gap and provide an in-depth analysis of injector port acylation of GHB with optimised conditions. The intention is for the work to be further developed with the use of chemical ionisation to improve analysis throughput. Fluorinated acid anhydrides were selected as they are the most commonly used acylation reagents. Trifluoracetic anhydride (TFAA), pentafluoropropionic anhydride (PFPA) and heptafluorobutyric anhydride (HFBA) were each given their own investigation.
The study found gradually increasing the temperature of the injector port had minor impact on derivatisation yields. The maximum was achieved at a constant temperature of 240 °C for an extended period. Different splits were investigated, it was found that reducing the split caused column overload, increased back pressure and system shut down. However, increasing the split meant derivatisation yields was significantly reduced, thus peak identification was inhibited. The optimum split was found to be 10:1 for TFAA and 5:1 for HBFA. Decreasing the source temperature increases the abundance of higher mass ions within the spectrum. This aids identification due to the specificity of the mass spectrum. However, the time spent achieving this reduces the analytical throughput, in a forensic context this can be detrimental to time-constrained cases. Each reagent supplied unique analytical benefits and drawbacks. Peak identification was easer in the TFAA chromatogram, while HFBA produced a more complex mass spectrum. A compromise between peak predominance and mass spectrum complexity could be
reached using PFPA.

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