Development of a thermal desorption modulator for gas chromatography

The separation space in gas chromatography can be enhanced dramatically by the comprehensive coupling of two independent separation dimensions. An interface between the two columns must accumulate analytes eluting from the first dimension, focus them and at the appropriate moment transfer them to the head of the second column. A thermal desorption modulator can be used for this purpose. It consists of a capillary in a relatively cold zone which effects trapping and focusing of the analytes. A current through a conductive material on the outside of the capillary provides rapid heating and consequently a fast transfer of the analytes to the second column. Several conductive materials were applied using different techniques and their performance was evaluated. The durability of thin metal coatings was found insufficient. The use of a wire coiled around the capillary was more robust and its temperature response appeared to be fast enough, despite the higher thermal mass. The effect of voltage and heating time on the thermal desorption was studied and various temperature estimations were made. Large-volume on-column re-injection and semi-comprehensive multidimensional gas chromatography of chlorobiphenyls are shown as examples.