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

Comprehensive two-dimensional gas chromatography (GC x GC) with a temperature-programmed microfabricated thermal modulator (mu TM) is demonstrated. The 0.78 cm(2), 2-stage mu TM chip with integrated heaters and a PDMS coated microchannel was placed in thermal contact with a solid-state thermoelectric cooler and mounted on top of a bench scale GC. It was fluidically coupled through heated interconnects to an upstream first-dimension (D-1) PDMS-coated capillary column and a downstream uncoated capillary or second-dimension (D-2) PEG-coated capillary. A mixture of n-alkanes C-6-C-10 was separated isothermally and the full-width-at-half-maximum (fwhm) values of the modulated peaks were assessed as a function of the computer-controlled minimum and maximum stage temperatures of mu TM, T-min, and T-max, respectively. With T-min, and T-max fixed at -25 and 100 degrees C, respectively, modulated peaks of C-6 and C-7 had fwhm values <53 ms while the modulated peaks of C-10 had a fwhm value of 1.3 s, due to inefficient re-mobilization. With T-min and T-max fixed at 0 and 210 degrees C, respectively, the fwhm value for the modulated C10 peaks decreased to 67 ms, but C-6 and C-7 exhibited massive breakthrough. By programming T-min from -25 to 0 degrees C and Tmax from 100 to 220 degrees C, the C-6 and C-7 peaks had fwhm values <= 50 ms, and the fwhm for C-10 peaks remained <95 ms. Using the latter conditions for the GC x GC separation of a sample of unleaded gasoline yielded resolution similar to that reported with a commercial thermal modulator. Replacing the PDMS phase in the mu TM with a trigonal-tricationic room temperature ionic liquid eliminated the bleed observed with the PDMS, but also reduced the capacity for several test compounds. Regardless, the demonstrated capability to independently temperature program this low resource mu TM enhances its versatility and its promise for use in bench-scale GC x GC systems. (C) 2016 Elsevier B.V. All rights reserved.