Width-Modulated Microfluidic Columns for Gas Separations

Microgas chromatography separation columns typically employ channels with fixed cross sections. In this paper, we demonstrate a new class of unidirectional microfabricated width-modulated columns (μWMC) that afford improved chromatographic efficiency, resolution, and retention times compared with corresponding constant width (120 μm) bidirectional columns. Two new μWMCs architectures are introduced: a linearly variable column (LVC) and a stepgradient column (SGC). The width of a 1-m long, 250-μm-deep LVC is gradually reduced from 120 to 20 μm at 1 μm/cm. While that of a 1-m-long SGC is modulated in five steps (120, 95, 70, 45, and 20 μm) each with a length of 20 cm. The effect of inlet selection (120 or 20 μm) on chromatographic performance is also evaluated. Moreover, with our improved fabrication process, multiple serially connected devices are simultaneously coated for the first time with highly stable silica nanoparticles utilizing layer-by-layer technique enabling constant film thickness.