Sample Preparation/Concentration for Trace Analysis in GC/MS (A study of solid phase microextraction and headspace sampling)
Wang, Yuwen Jr.
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Solid Phase Microextraction (SPME) associated with Microwave Assisted Extraction (MAE)(1-3) , on-line headspace derivatization (4-6) and the selectivity of different SPME coatings (7) were studied. Trace amounts of Veltol ®, Veltol Plus® and short chain fatty acids in food samples were analyzed by GC/MS. Since SPME is not directly applicable to solid samples, SPME associated with MAE techniques was studied for solids, primarily food samples. The efficiency of classical solvent extraction and MAE was compared. The parameters which affect SPME, were optimized for the determination of Veltol® and Veltol Plus® in food products such as potato chips and coffee. The technique gave a detection limit of 2 ppb for Veltol Plus ® which is 200 times more sensitive than conventional GC technique. Headspace injection is characterized by simple and easy handling of complicated solid and solution matrices. Headspace injection, however, is not suitable for high molecular weight substances or non-volatile compounds. An on-line derivatization headspace technique was studied for short chain fatty acids. These samples are difficult to do by classical GC. The developed technique simplified the conventional derivatization procedures and combined the sample preparation and GC/MS analysis into one step. The thermostatting temperature, time, solvent and matrix effects were investigated. Low calorie fat and some agricultural samples were analyzed. The detection limit for acetic acid is 8 ppb. SPME is a novel sample introduction technique. The behavior of di(methylsiloxane), polyacrylate and Carbowax coatings on SPME fibers for compounds having different functional groups were investigated. The selectivities of the coating, sample pH and the sample temperature were investigated.
- Doctoral Dissertations