Development and validation of novel solventless microextraction techniques in gas chromatography

Among the prior demands in current sample preparation for organic trace analysis are sensitivity, ease of automation and solvent exclusion. One approach to meet these demands has been the development of microextraction techniques, where the amount of extraction phase is very small compared to the sample phase. Today, microextraction techniques are used in current analytical methods from all fields. This thesis provides an overview on the recent developments in solventless microextraction techniques, with special emphasis on techniques providing full automation, starting from the first open-tubular trap techniques in the mid-1980s to recent devices utilizing sorbent packed needles. Different implementations of in-needle microextraction are discussed with their characteristic benefits, shortcomings and possible sampling modes. In this context, solid phase dynamic extraction (SPDE) was investigated for its applicability in quality control analysis of 196 German red wines. To that purpose, a fingerprinting database was created using commercial available chromatogram comparison software. 22 flavor relevant alcohols and esters have been quantified, also, to monitor the long term extraction performance of the SPDE needles, which showed constant results for up to 400 extractions using one extraction needle tip. A novel in-tube extraction (ITEX) device for headspace sampling has been evaluated for environmental and food analysis. To that end, five commercially available and six custom prepared sorbent traps have been evaluated for their extraction efficiency for over 50 analytes from different classes. They cover aromatics, heterocyclic aromatics, halogenated hydrocarbons, fuel oxygenates, alcohols, esters and aldehydes. During this course, the benefits of the use of adsorbent or absorbent materials, depending on the application, were shown, as well as the potential of mixed bed traps. Method detection limits in the low ng L-1-range were achieved for compounds of importance for drinking water quality, which is much lower than demanded by regulatory limits and usually requires much more complex purge and trap systems. Furthermore, it was possible to discriminate the six beer varieties Alt, Helles, Kölsch, Pilsener beer, Schwarzbier and wheat beer and to assign 46 beers to these classes, just by analyzing volatile aroma constituents and applying Linear Discriminant Analysis. The governing parameters of the extraction and injection steps are discussed and the experiences from method development are summarized to give recommendations for the setting of proper extraction conditions, in order to minimize the experimental effort for future method development.Zu den wichtigsten Anforderungen in der aktuellen organischen Spurenanalytik gehören Empfindlichkeit, leichte Automation und die Vermeidung von Lösemitteln. Ein Ansatz diese Ziele zu erreichen war die Einführung von Mikroextraktionstechniken, bei denen die Menge der Extraktionsphase, im Vergleich zur Probenphase, sehr klein ist. Heute werden Mikroextraktionstechniken in vielen analytischen Gebieten angewandt. Diese Arbeit bietet einen Überblick über die Entwicklung lösemittelfreier Mikroextraktionstechniken, mit vornehmlichem Schwerpunkt auf vollständig automatisierbare Techniken, beginnend bei den ersten Kapillartechniken Mitte der 1980er Jahre, bis hin zu aktuellen Ausführungen mit gepackten Nadeln. Die Verschiedenen Varianten werden in Bezug auf ihre charakteristischen Vor- und Nachteile und ihre Einsatzmöglichkeiten diskutiert. In diesem Zusammenhang wurde die Solid Phase Dynamic Extraction (SPDE) auf ihre Anwendbarkeit in der Qualitätskontrolle von 196 deutschen Rotweinen untersucht. Dazu wurde mit einer kommerziellen Vergleichssoftware eine Datenbank erstellt, mit der bekannte Proben identifiziert werden können. Weiterhin wurden 22 Geschmacksrelevante Alkohole und Ester quantifiziert und anhand dieser Daten die Langzeitstabilität der SPDE Nadeln untersucht. Mit einer Nadel konnten, bei konstanter Leistung, bis zu 400 Analysen durchgeführt werden. Eine neuartige In-tube Extraction (ITEX) Einheit wurde für die Umwelt- und Lebensmittelanalytik evaluiert. Dabei wurde die Extraktionseffizienz von fünf kommerziell erhältlichen und sechs speziell angefertigten Extraktionsnadeln anhand von über 50 Analyten verschiedener Klassen verglichen. Sie umfassten Aromaten, Heteroaromaten, halogenierte Kohlenwasserstoffe, Treibstoffzusätze, Alkohole, Ester und Aldehyde. Dabei wurden die anwendungsspezifischen Vorteile von Ab- und Adsorbtionsmaterialien und die Möglichkeiten gemischter Extraktionsphasen gezeigt. Für trinkwasserrelevante Analyten wurden Nachweisgrenzen im unteren ng L-1-Bereich erzielt, die weit unter den erforderlichen Grenzwerten liegen und sonst nur mit deutlich komplexeren Purge & Trap Systemen erreicht werden. Weiterhin war es durch Messung von flüchtigen Geschmacksstoffen möglich, die sechs Biervarianten Alt, Helles, Kölsch, Pils, Schwarzbier und Weizen zu Unterscheiden und 46 Biere, durch lineare Diskriminanzanalyse, ihrer entsprechenden Variante zu zuordnen. Mit den Erfahrungswerten der Methodenentwicklung werden die entscheidenden Parameter der Extraktions- und Injektionsschritte diskutiert und Empfehlungen für geeignete Bedingungen gegeben, um den Entwicklungsaufwand für zukünftige Methoden zu minimieren

GridLabs: Facilitating collaborative access to remote laboratories

eScience is usually characterized by the cooperation of distributed groups of researchers who share data and computing environments and perform experiments together. Often immense data sets that were produced by expensive equipments need to be accessed and evaluated. Such eScience scenarios require both, support for collaboration of researchers at distant locations and also the remote control of the shared laboratory devices. However, this type of remote experimentation and collaboration must be taught during university education. In this paper, we propose a framework that supports the training of above practices through the provision of a dedicated collaboration environment. It extends current approaches with support for a life cycle of remote labs, including scheduling the access to remote labs as well as defining access permissions. Our experiences in teaching lab courses suggest that the approach is also applicable in eScience scenarios

Polymerase chain reaction to search for Herpes viruses in uveitic and healthy eyes: a South African perspective

Objective: To analyse aqueous polymerase chain reaction (PCR) results in patients diagnosed with undifferentiated uveitis and determine prevalence of herpesviridae in non-uveitic patients undergoing routine cataract extraction. Design: Retrospective comparative case series and prospective cross-sectional study. Subjects: 72 patients with idiopathic uveitis and 57 surgical patients. Methods: Diagnostic aqueous paracentesis with PCR testing for 6 herpes viridae in uveitic patients. Anterior chamber paracentesis immediately pre-operative in the prospective arm, with PCR testing. Results: In the retrospective review we had a 47.2% positive PCR yield. Data analysis revealed a statistically significant correlation between a positive yield and being HIV+ (p=0.018); between an EBV+ yield and being HIV+ (p= 0.026) and a CMV+ result and being HIV+ (p=0.032). Posterior uveitis (p=0.014) and symptoms <30 days (p= 0.0014) had a statistically significant yield. In the prospective arm of the study: all 57 patients were HIV- and all aqueous samples were negative for the 6 herpesviridae. Conclusion: We recommend PCR testing for Herpesviridae as a safe second line test for patients with undifferentiated uveitis. We were unable to establish prevalence and suggest that the idea of a commensal herpes virus is unlikely if the blood-ocular barrier is intact

Volatile fingerprinting differentiates diverse-aged craft beers

Supplementary data to this article can be found online at https:// doi.org/10.1016/j.lwt.2019.03.044.Beer ageing on wood is a complex and difficult to control process involving several reactions and compounds. Difficulties in understanding the underlying phenomena often lead to empirical and unpredictable processes and heterogeneous products. This work resorts to volatile fingerprinting along with multivariate analysis as tools to differentiate and highlight differences in beers derived from diverse production processes. Volatile composition of beers originating from barrel ageing processes and unaged beer were analyzed by GC-MS. The collected data was processed by principal component analysis, which allowed the evaluation of relations between samples and volatile compounds. Beers were distinguished by clusters comprising different groups of volatiles. Beer with the longest period in barrel was in the cluster with the most volatiles. Beer produced by resident barrel microbiota fermentation was characterized by presence of Brettanomyces sp. metabolites. Beer aged in barrel by a shorter time period showed characteristic content of ethyl esters and oak extractives. Beer produced in inox vat and beer fermented in barrel with pitching of S. cerevisiae appeared in the same cluster, relating with fermentative esters. Volatile fingerprinting was a viable approach to characterize and distinguish the analyzed beers, providing relevant information regarding the impact of production methodologies in volatile composition.This work had funding support of the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2019 unit and COMPETE 2020 (POCI-01-0145 FEDER-006684) and BioTecNorte operation (NORTE-01-0145-FEDER000004) funded by the European Regional Development Fund under the scope of Norte2020 – Programa Operacional Regional do Norte. Fermentum –EngenhariadasFermentações Lda.also participated incofunding and supplying materials for this work. Authors would like to thank Mr. Paulo Coutinho and Quinta do Portal for supplying the oak barrels used in this work.info:eu-repo/semantics/publishedVersio

A multi-user multiprocessor computer system

Thesis (M. Ing.) -- University of Stellenbosch, 1988.Full text to be digitised and attached to bibliographic record

A multi-user multiprocessor computer system

Thesis (M. Ing.) -- University of Stellenbosch, 1988.Full text to be digitised and attached to bibliographic record