A rapid and variable-volume sample loading scheme for nonaqueous microchip electrophoresis with laser induced fluorescence detection (NAMCE-LIF) was developed, which included a porous polymer plug, a low-cost microvacuum pump, and a single potential supply. The porous polymer plug was fabricated within the separation channel as a select valve, which prevented the running buffer from buffer waste reservoir (BW) flowing back into the separation channel, but allowed electrophoretic migration along the separation channel. By applying a subatmospheric pressure to the headspace of sample waste reservoir (SW), sample and running buffer were drawn immediately to SW. At the same time, a branch of the sample stream was driven across the porous polymer plug by the electric force and formed a sample zone in the separation channel. The injected sample zone length was in proportion with the injection time. The proposed method was successfully applied to separation of Rhodamine 123 (Rh123) and Rhodamine 6G (Rh6G). The limits of detection for Rh123 and Rh6G based on S/N = 3 were 0.63 and 0.48 nmol L- 1, respectively. The system has been proved to possess an exciting potential for improving throughput, repeatability, sensitivity, separation performance of nonaqueous microchip electrophoresis and a wide range of applications.
variable-volume sample loading; nonaqueous microchip electrophoresis; negative pressure; porous polymer plug; electrokinetic force
