Comprehensive Two-Dimensional Gas Chromatographic Separations with a Microfabricated Thermal Modulator

Abstract

Rapid, comprehensive two-dimensional gas chromatographic (GC × GC) separations by use of a microfabricated midpoint thermal modulator (μTM) are demonstrated, and the effects of various μTM design and operating parameters on performance are characterized. The two-stage μTM chip consists of two interconnected spiral etched-Si microchannels (4.2 and 2.8 cm long) with a cross section of 250 × 140 μm(2), an anodically bonded Pyrex cap, and a cross-linked wall coating of poly(dimethylsiloxane) (PDMS). Integrated heaters provide rapid, sequential heating of each μTM stage, while a proximate, underlying thermoelectric cooler provides continual cooling. The first-dimension column used for GC × GC separations was a 6 m long, 250 μm i.d. capillary with a PDMS stationary phase, and the second-dimension column was a 0.5 m long, 100 μm i.d. capillary with a poly(ethylene glycol) phase. Using sets of five to seven volatile test compounds (boiling point ≤174 °C), the effects of the minimum (T(min)) and maximum (T(max)) modulation temperature, stage heating lag/offset (O(s)), modulation period (P(M)), and volumetric flow rate (F) on the quality of the separations were evaluated with respect to several performance metrics. Best results were obtained with a T(min) = -20 °C, T(max) = 210 °C, O(s) = 600 ms, P(M) = 6 s, and F = 0.9 mL/min. Replicate modulated peak areas and retention times were reproducible to <5%. A structured nine-component GC × GC chromatogram was produced, and a 21 component separation was achieved in <3 min. The potential for creating portable μGC × μGC systems is discussed.

Comprehensive two-dimensional gas chromatographic separations with a temperature programmed microfabricated thermal modulator

“…The two-stage µTM has been described previously [29][30][31][32][33]. The μTM used for most testing was statically coated with PDMS from a solution that also contained 1% (w/w) dicumyl peroxide as the crosslinking agent using a published procedure [40,41].…”

“…In a departure from our previous μTM mounting schemes [29][30][31][32][33], a small swatch of thermally conductive silicone material (Sil-Pad, Henkel, Chanhassen, MN) was placed against the heater on the Pyrex side of each stage, and held there with a thin film of thermal paste. Two small, square slabs of Si were then coated on both sides with thermal paste and placed on top of the Sil-Pad swatches.…”

“…Inspired by this approach, we were interested in incorporating a similar feature into the microfabricated thermal modulator (μTM) on which we have reported recently [29][30][31][32][33]. First described in 2010 [29,30], this µTM is cryogen-free and requires much less power to operate than conventional TMs.…”

“…It consists of a single, Pyrex-sealed Si microchannel with two thermally isolated spiral sections, or stages, each with independent thin-metal-film heaters. The µTM is mounted on a solid-state thermoelectric cooler (TEC) capable of maintaining T min as low as -35 o C, and it can be heated rapidly to > 250 o C and then cooled again with modulation periods, P m , as short as 5 s. We have used this device in GC  GC separations with conventional capillary columns [30,31], and in GC  GC separations with microfabricated columns [32] and, most recently, with a polymer-coated, microfabricated optofluidic ring resonator (µOFRR) as the detector [33].…”

Micro Total Analysis Systems: Fundamental Advances and Applications in the Laboratory, Clinic, and Field

“…Recent advances in this area have included a water-activated, self-heating cartridge for a nucleic acid amplification chip 231 and a microfabricated thermal modulator for sample transfer in 2D gas chromatography. 232 Advances in self-powered devices included integrated batteries capable of powering electrochromic detection, 233 an on-chip fuel cell that supplied electrical and pumping power (Figure 9a), 234 and galvanic cells that powered an LED when sample was added to a paper-based device. 235 Another autonomous system was a lab-on-a-robot, which contained a temperature-controlled microfluidic device integrated with capillary electrophoresis that could be operated by long-range remote control on an all-terrain vehicle.…”