The overall capacity of the microcolumn (C18, 5 μm beads, 20 mm × 1 mm × 0.1 mm) was calculated to be 0.45 μg/mm packing for the Cr(VI). Although the demonstrated microchip included only 20 mm length of packings, the lengths can be largely (e.g. 10 ×) increased if serpentine and curved channels are used for the packing; thus, the capacity of the microcolumn will be increased as well. Theoretically, the capacity of the column could be increased by thicker packings; however, the thickness of the channel created in the PDMS microchip using soft lithography [24] was not allowed to exceed a maximum of around 0.1 mm.