DEVELOPMENT OF A THERMAL-DESORPTION MODULATOR FOR GAS-CHROMATOGRAPHY

The separation space in gas chromatography can be enhanced dramaticall y by the comprehensive coupling of two independent separation dimensio ns. An interface between the two columns must accumulate analytes elut ing 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 anal ytes. A current through a conductive material on the outside of the ca pillary provides rapid heating and consequently a fast transfer of the analytes to the second column. Several conductive materials were appl ied using different techniques and their performance was evaluated. Th e durability of thin metal coatings was found insufficient. The use of a wire coiled around the capillary was more robust and its temperatur e 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 o n-column re-injection and semi-comprehensive multidimensional gas chro matography of chlorobiphenyls are shown as examples.