Συντάχθηκε 22-09-2014 12:21
από Evaggelia Giantzi
Email συντάκτη: egiantzi<στο>tuc.gr
Ενημερώθηκε:
-
Κύρια: εξ. συνεργάτης.
Άλλες ιδιότητες: απόφοιτος ΜΔΕ/Διδ. ΜΗΠΕΡ
Παρουσίαση της διδακτορικής διατριβής με θέμα:
«Microextraction under vacuum conditions»
Ημερομηνία παρουσίασης: Παρασκευή 26 Σεπτεμβρίου 2014 και ώρα 13.00
Αίθουσα: Μ4.001 (κτίρια ΜΗΧΟΠ)
Υποψήφια Διδάκτωρ: Γιαντζή Ελίνα
Επταμελής Εξεταστική Επιτροπή:
1. Αναπληρώτρια Καθηγήτρια Έλια Ψυλλάκη (επιβλέπουσα)
2. Καθηγητής Νικόλαος Καλογεράκης
3. Καθηγήτρια Marta Lores
4. Καθηγητής Κωνσταντίνος Χρυσικόπουλος
5. Καθηγητής Νικόλαος Καλλίθρακας – Κοντός
6. Καθηγητής Ευάγγελος Διαμαντόπουλος
7. Αναπληρωτής Καθηγητής Ιωάννης Κωνσταντίνου
Περίληψη
The present thesis investigates the possibility of sampling semi – volatile analytes from the headspace of an aqueous sample using headspace solid – phase microextraction (HSSPME) under vacuum conditions. The new procedure was termed vacuum assisted headspace solid phase microextraction (Vac-HSSPME).
The proposed procedure ensured reproducible conditions for HSSPME and excluded the possibility of analyte losses. Although reduced pressure conditions during HSSPME sampling are not expected to increase the amount of analytes extracted at equilibrium, they greatly increase extraction rates compared to HSSPME under atmospheric pressure due to the enhancement of evaporation rates in the presence of an air-evacuated headspace. The effect is larger in semivolatiles, whose evaporation rates are controlled by mass transfer resistance in the thin gas film adjacent to the sample/headspace interface.
It was demonstrated that for low KH analytes, where mass transfer from the sample to the headspace is the rate-determining step, HSSPME extraction rates increase when sampling under vacuum conditions due to the enhancement of evaporation rates. Therefore, higher extraction efficiency and sensitivity can be achieved with Vac-HSSPME within short sampling times and under mild conditions (eg. lower temperatures). The KH value may be used to predict the performance of Vac-HSSPME. For analytes close or below the reported threshold values for low KH solutes, extraction kinetics are considerably improved with Vac-HSSPME compared to regular HSSPME, as evaporation rates for these analytes dramatically increase under reduced pressure conditions and consequently the sample responds much faster to the concentration drops in the headspace. For these compounds the faster replenishment of the analytes’ headspace concentrations also explained the fact that extraction kinetics was largely not affected by the tested change in headspace volume. Conversely, for intermediate KH solutes where liquid-phase resistance to mass transfer becomes important, Vac-HSSPME will not lead to obvious improvements in extraction rates compared to regular HSSPME.
Furthermore, Vac-HSSPME was successfully applied to the analysis of sandy soil samples. It was demonstrated that heating the dry sandy soil samples during Vac-HSSPME further enhanced extraction kinetics, while the presence of water during Vac-HSSPME was found to be essential and improved the sensitivity of the proposed method. Heating sand samples in the presence of a small amount of water enhanced extraction kinetics up to a certain temperature above which the presence of water molecules in the headspace was found to impair the partitioning of the target analytes with the SPME fiber. Thus, Vac-HSSPME confirmed that very good sensitivity and precision could be attained within short sampling times and under mild sampling temperatures.
Moreover, the automation of Vac-HSSPME has been made possible by downsizing the sampling containers. To overcome problems associated with the small openings and the orientation of the commercially available gas sampling chambers, custom-made glass sample containers having total volumes of 1000, 500, 40 and finally 22 mL were used as sampling chambers. The 22 and 40 mL modified sample vials offer ease in handling and significant analytical performance. This is the first work indicative of the automation potential, of such an efficient methodology, destined for routine laboratories.
