Then, the adsorbed (preconcentrated) Cr(VI) can be eluted from the microcolumn by pumping the eluent from the common port E (elution). In this case, all adsorbed Cr(VI) will be eluted from all microcolumns at the same time, but the elution from a given channel can be prevented by blocking the port S of any microcolumns. A schematic depiction of the sample loading and elution is given in Fig. 1c.