A Robust Micro Thermal Modulator for Comprehensive GC x GC Gas Chromatography

Schematic of micro Thermal Modulator (uTM) (b) Detector signal of VOC complex mixture modulated by the uTM

Comprehensive two-dimensional gas chromatography (GCxGC) is a powerful analytical technique to separate and detect the components of complex mixtures of volatile organic compounds. Focusing and re-injecting eluting mixture components, a thermal modulator placed be­tween two separation columns in a GC×GC system plays a critical role in enhancing the resolution and the selectivity of analytes. As part of our efforts to develop a μGC×μGC prototype, we have designed, fabricated, and operated a two-stage, microfabricated thermal modulator (μTM) using MEMS technology. It contains two sequential serpentine Pyrex-on-Si microchannels (stages) that cryogenically trap analytes eluting from the first-dimension column and thermally inject them into the second-dimen­sion column. The μTM is kept approximately at -20°C by a solid-state thermoelectric cooling unit placed a few tens of microns from the de­vice, and for each rapid modulation cycle it is heated to 210°C at 2400°C/s by integrated resistive microheaters and then cooled back to -50°C at -168°C /s. Thermal crosstalk between the two stages is less than 9%. We have successfully demonstrated the first MEMS based micro-Thermal modulator for 2D GC with fast thermal response and low power consumption (~10 W), which is 2 orders of magnitude lower than conventional TMs, and drastically smaller size. Further there is no use of cryogenic consumables. Peak enhancements of ~ 45-50 and full width at half height of ~ 90 have been obtained. Initial characterization by coupling the thermal modulator with 1st and 2nd dimension channels to yield a 2d GCxGC chromatogram. However the performance can still be drastically improved.