At-column heating and a resistively heated, liquid-cooled thermal modulator for a low-resource bench-top GC x GC

A transportable GC x GC instrument is under development for on-site applications that would benefit from the enhanced resolution and powers of detection, which can be achieved by this method. In the present study, a low-resource GC x GC instrument using an electrically heated and liquid-cooled single-stage thermal modulator that requires no cryogenic materials is evaluated. The instrument also uses at-column heating, thus eliminating the need for a convection oven to house the two columns. The stainless-steel modulator tube is coated with PDMS, which can be heated to 350 degrees C for sample injection into the second-dimension column. The modulator is cooled to -30 degrees C by a 100 mL/min flow of PEG by means of a commercial liquid chiller and a small recirculating pump. Resistive heating of the modulator tube is provided by a programmable power supply, which uses a voltage program that results in increasing modulator temperature during an analysis. This, together with more rapid cooling by the use of a liquid cooling medium, results in reduced solute breakthrough following each heating cycle as the modulator cools to a temperature where quantitative trapping resumes. As a result, modulated peak widths at half-height of less than 40 ms are observed. Design and performance details are presented along with chromatograms of gasoline and an essential oil sample.