Design and performance evaluation of a two-stage resistively-heated thermal modulator for GC × GC

Abstract

The design and performance evaluation of a two-stage resistively-heated thermal modulator that does not use any cryogenic consumables is described. A commercially available piece of stainless-steel wall coated capillary column is used as the modulator. Cooling of the modulator is provided by a two-stage refrigeration unit with an external heat exchanger and a closed-loop recirculating air system. The modulator is resistively heated by sending a current pulse through each stage of the modulator tube. Studies evaluating the modulator trapping efficiency, cooling efficiency, desorption efficiency, and resultant peak shape are presented and discussed. Performance evaluation of this modulator is compared to similar single-stage modulators, both qualitatively and quantitatively, and has exceeded the previous data reported for the single stage versions. GC × GC chromatograms of a C₆-C₂₀ n-alkane mixture, a petroleum sample, and a 38-component mixture of aliphatic, aromatic, and halogenated volatile organic compounds are provided. This two-stage modulator proves to be a viable alternative to commercially available modulators which require large amounts of cryogenic fluids.