Direct On-Line Injection in Capillary Electrophoresis

A direct method of sample introduction for capillary electrophoretic techniques is described using a cross configuration and high-voltage shunting. No physical disturbance of the separation capillary inlet is required, and the feasibility of direct on-line injection is demonstrated. Both full- and pinched-mode injections are evaluated, with pinched-mode injections showing superior performance. In the pinched mode, only a portion of the cross volume is introduced onto the separation capillary, as a result, a lower volume is injected, and wall effects within the cross are minimized. Preliminary studies indicate a peak height reproducibility for replicate injections of better than 4.1%, with area reproducibilities of less than 3.1% for nonoverlapping solutes. Utilizing this direct on-line injection method, many rigid or restricted capillary geometries can be accommodated, and extension to the wide range of capillary electrophoretic techniques is feasible.