Large Volume Injection and Hyphenated Techniques for Gas Chromatographic Determination of PBDEs and Carbazoles in Air
Sammanfattning: This thesis is based on studies in which the suitability of various gas chromatography (GC) injection techniques was examined for the determination of polybrominated diphenyl ethers (PBDEs) and carbazoles, two groups of compounds that are thermally labile and/or have high boiling-points. For such substances, it is essential to introduce the samples into the GC system in an appropriate way to avoid degradation and other potential problems. In addition, different types of gas chromatographic column system and mass spectrometric detectors were evaluated for the determination of PBDEs.Conventional injectors, such as splitless, on-column and programmed temperature vaporizing (PTV) injectors were evaluated and optimized for determination of PBDEs. The results show on-column injection to be the best option, providing low discrimination and high precision. The splitless injector is commonly used for “dirty” samples. However, it is not suitable for determination of the high molecular weight congeners, since it tends to discriminate against them and promote their degradation, leading to poor precision and accuracy. The PTV injector appears to be a more suitable alternative. The use of liners reduces problems associated with potential interferents such as polar compounds and lipids and compared to the hot splitless injector, it provides gentler solvent evaporation, due to its temperature programming feature, leading to low discrimination and variance.Increasing the injection volume from the conventional 1-3 µL to >50 µL offers two main benefits. Firstly, the overall detection and quantification limits are decreased, since the entire sample extract can be injected into the GC system. Secondly, large volume injections enable hyphenation of preceding techniques such as liquid chromatography (LC), solid phase extraction and other kinds of extraction. Large-volume injections were utilized and optimized in the studies included in this thesis.With a loop-type injector/interface large sample volumes can be injected on-column providing low risk of discrimination against compounds with low volatility. This injector was used for the determination of PBDEs in air and as an interface for the determination of carbazoles by LC-GC. Peak distortion is a frequently encountered problem associated with this type of injector that was addressed and solved during the work underlying this thesis.The PTV can be used as a large volume injector, in so-called solvent vent mode. This technique was evaluated for the determination of PBDEs and as an interface for coupling dynamic sonication-assisted solvent extraction online to GC. The results show that careful optimization of the injection parameters is required, but also that the PTV is robust and yields reproducible results.PBDEs are commonly detected using mass spectrometry in electron capture negative ionization (ECNI) mode, monitoring bromine ions (m/z 79 and 81). The mass spectrometric properties of the fully brominated diphenyl ether, BDE-209, have been investigated. A high molecular weight fragment at m/z 486/488 enables the use of 13C-labeled BDE-209 as an internal surrogate standard.
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