Design, development and evaluation of a resistively-heated thermal modulator for comprehensive two-dimensional gas chromatography.

摘要

Comprehensive two-dimensional gas chromatography (GCxGC) is regarded as one of the most powerful methods for complex sample analysis. The very large peak capacity, structured chromatograms and increased detectibility are favorable attributes that make GCxGC a routinely used analytical technique for the analysis of petroleum, forensic, fragrance and even human breath samples. The heart of any GCxGC is the modulator which focuses effluent from the first column and subsequently re-injects this trapped aliquot as a narrow sample plug for a second, often very rapid, analysis on a micro-bore capillary column. While current commercially available thermal modulators work very well, the success of these modulators is coupled with a large amount of liquid nitrogen that is used for cryogenic trapping. In order to make GCxGC a consumable free technique as well as miniaturized and field portable, a thermal modulator has been developed which does not require the use of liquid nitrogen or any other consumable. The modulator is cooled by means of a two-stage refrigeration unit and a recirculating pump that continually circulates cold dry air or chilled liquid. In order to release trapped components, the modulator is resistively-heated by a dc power supply. The work presented will discuss the design and development as well as showcase the evaluation of single-stage and two-stage resistively-heated thermal modulators. Experimental results have shown a dynamic range of over three orders of magnitude with an injection plug width at half-height to be less than 20 ms for hydrocarbon components. Sample analysis of petroleum, multi-component test mixtures and human breath samples will be presented in this work.