Transient isotachophoresis of highly saline samples using a microchip

Transient isotachophoresis (TITP) of a highly saline solution has been achieved on a polydimethylsiloxane chip of 18 mm × 12 mm. The microchannel dimensions were 30 μm in width and 30 μm in depth. The injection plug length was varied from 12 to 28 mm to inject samples of large volume while the total channel length was fixed at 75 mm. Chloride ions abundant in the saline sample and N-tris(hydroxymethyl)methyl-3-aminopropanesulfonate ions in the background electrolyte were used respectively as the leading and terminating electrolytes for TITP of anionic analytes fluorescein and 2,7-dichlorofluorescein. Electrokinetic injection of a large volume sample and subsequent TITP process were performed with simple electric controls. Five hundred-fold improvement in 250 mM NaCl solution could be achieved in 2 min and the limit of detection (S/N = 3) was estimated as 3 pM in our home-made laser induced fluorescence setup with BGE of 95 mM TAPS and 73 mM TEA, and 0.05 vol.% FC-PN (pH 9.0). The real-time progress of TITP on a microchip was also visualized using a video microscope.