New Concepts and Techniques for Quantification and Trace Analysis by Gas Chromatography

In the first part of this thesis, strategies for avoiding systematic errors when quantifying the main components in mixtures of solvents has been developed (paper I). It is shown that variations in density caused by variations in sample composition and/or volume contraction need to be taken into account. In this way, quantification can be improved. The second part (paper II-V) describes a number of new methods for the analysis of organic trace components present in gaseous or aqueous samples, after an overview of the most commonly applied sample enrichment techniques has been given. For the enrichment of volatile trace compounds from gaseous samples, the concept of open tubular trapping has been further developed. A simplified procedure for preparing ultra-thick film, sorptive open tubular traps (OTTs) is described (paper III). The traps are coated with an irregular film of PDMS, and it is shown that the performance in terms of breakthrough volume is only marginally affected by the use of such traps. In paper IV, it is shown both experimentally and with a theoretical model that the enrichment capacity of OTTs can be significantly increased by increasing the inner diameter of the traps. A fully automated procedure for high-capacity sorption enrichment of trace organic analytes present in water is also reported (paper II). Time-based non-equilibrium extractions are feasible, enabling fast extractions that still allow sub-ppt limits of detection. The high flexibility of the automated system makes it possible to sample from process streams or off-line sources. Finally, the development of a new 2-dimensional precolumn-backflush method for the analysis of polar volatile trace analytes in water is described (paper V). This concept is based on the action of a hygroscopic salt which has a strong affinity for water, in a precolumn. Organic trace compounds, such as volatile alcohols or ketones show little retention on the precolumn and are eluted ahead of the bulk amount of the water onto a capillary column for subsequent high resolution separation. The residual water is removed from the system by backflushing the precolumn. The procedure allows the direct injection of aqueous sample volumes of at least 100 μl, and the pre-fractionation is accomplished within only a few minutes. Quantification limits for selected polar trace components were in the low ppb-region.