Practical limitations of capillary gas chromatography

Abstract

SummaryGlass capillary gas chromatography is a high resolution separation method which allows the qualitative and quantitative analysis of even complex mixtures, which may contain many components -also isomeric -in a wide range of volatilities, polarities and concentrations.The principal limitation of gas chromatographic application is given by an insufficient volatility of the species to be separated. Elevated temperatures have to be applied if the application range is to be extended and to achieve steep peak profiles, i.e. low detection limits at high resolution. The use of elevated temperatures is limited, of course, by the temperature stability of both the solvent (stationary liquid and support) and the solutes.The problems of trace analysis for low volatility compounds at high resolution and its limitational parameters regarding sampling, separation and detection are discussed.The applicability of glass capillary columns in this field is influenced by the following parameters: tailing behaviour; irreversible adsorption of polar and decomposition of unstable solutes; thermal stability of stationary liquid (including the support deactivation); separation efficiency and sample capacity (film thickness).Multidimensional gas chromatography using capillary columns coupled either with a packed or another capilllary column for preseparations may be applied with advantage in the analysisof complex mixtures.The basic idea of a discussion on the limitations of a powerful analytical high performance method like capillary gas chromatography [l] may originate from different sources.Firstly, there will be a discussion on future developments to elucidate the lines of development which may be more promising than others and to rule out those activities which probably are without chance for principal or theoretical reasons. Moreover the inadequate application of the method, i.e. without regarding its limitations, by the analytical chemists, who are usually not in the position to spend time on systematic investigations, has created a critical attitude towards capillary gas chromatography which is thought of as inadequate regarding its capabilities and advantages even for routine analyses.Orthodox opinions, and even prejudices have been expressed until recently. But there is no longer any excuse for not making use of high performance capillary gas chromatography, faced with the extremely complicated volatile mixtures to be analyzed today.What are the limiting factors which could determine the optimization of practical gas chromatographic analysis? (a)Too much time has to be spent, depending on the required resolution and on the chromatographic volatility of the species to be determined.(b) Too low a level of detection is achieved (i.e. low signal to noise ratios at maximum detector sensitivity as a consequence of broad and distorted (tailed) peak profiles.(c) The qualitative (retention) andlor quantitative data are neither reproducible nor accurate.Limiting factors of more principal importance for optimal gas chromatographic ana...

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