High-speed, temperature programmable gas chromatography utilizing a microfabricated chip with an improved carbon nanotube stationary phase

A new growth recipe for producing carbon nanotubes (CNTs) combined with a new bonding technique was implemented in a microfabricated gas chromatography (micro-GC) chip. Specifically, the micro-GC chip contained a 30-cm (length) microfabricated channel with a 50 μm × 50 μm square cross-section. A CNT stationary phase “mat” was grown on the bottom of the separation channel prior to the chip bonding. Injections onto the micro-GC chip were made using a previously reported high-speed diaphragm valve technique. A FID was used for detection with a high-speed electrometer board. All together, the result was a highly efficiency, temperature programmable (via low thermal mass, rapid on-chip resistive heating) micro-GC chip. In general, the newly designed micro-GC chip can be operated at significantly lower temperature and pressure than our previously reported micro-GC chip, while producing excellent chemical separations. Scanning electron microscopy (SEM) images show a relatively thin and uniform mat of nanotubes with a thickness of ∼800 nm inside the channel. The stationary phase was further characterized using Raman spectroscopy. The uniformity of the stationary phase resulted in better separation efficiency and peak symmetry (as compared to our previous report) in the separation of a mixture of five n-alkanes (n-hexane, n-octane, n-nonane, n-decane and n-undecane). The on-chip resistive heater employing a temperature programming rate of 26 °C/s produced a peak capacity of eight within a 1.5-s time window.