Although the minimal uptake demand for sensitive FAAS detection is around 30 μL, this sample volume is still enormously large for typical microfluidic applications. In our earlier [11] and [12] and others' [13] chip-based chromatographic works, even less than 0.1 μL volume of sample was eluted from the microcolumns. In order to increase the effluent volume, the dimensions of microcolumns were maximized. The soft lithographic procedure [24] used for the microchip preparation enables a 0.1 mm maximal height of the microchannel (the SU-8 2025 photoresist was spincoated with a low speed for short time). The width of a microcolumn was increased to 1 mm (in other chip-based chromatographic work, the widths are 0.1 mm [11], [12] and [13]). The length of the microcolumns was limited by the width of the glass slide. After these considerations, the dimension of the microcolumns was 20 mm × 1 mm × 0.1 mm (Fig. 1b), which was useful to produce effluent (after separation or preconcentration of components) in a range of 10–30 μL. These chip-based chromatographic columns already can serve enough volume of sample for the micro-injection FAAS.