Plastic microchip mediated coupling of capillaries for flow pinched sample injection and consecutive electrophoretic analysis

Capillary electrophoresis (CE) is a powerful separation tool for multicomponent analysis, but the necessity of switching the inlet end of the capillary between the vials of sample and running buffer for the sample injection complicates the operation and contributes to the irreproducibility, leading to poor compatibility with on-line analysis. Herein, coupling of capillaries with the aid of a plastic microchip was achieved for consecutive analysis. An assembly of 3 pieces of capillary with a cyclic olefin copolymer (COC) microchip was fabricated by thermal bonding of the COC plates with capillaries embedded in the micro-grooves with a cross-type configuration. Two capillaries acted as a sampling channel and the third capillary was used for separation. A buffer reservoir was installed on the microchip, which connected to the joint of the capillaries. The relative liquid levels of this reservoir and the vials at the other ends of the capillaries determine the length of the sample plug. With this assembly, the RSD of peak height and peak area for consecutive analysis were 0.54 % and 2.27 % (n = 9), the sample carryover was less than 0.32 %. The applicability of the device was confirmed by monitoring the leaching process of K + in a green tea and vitamin C effervescent tablets.