A Sample Introduction Method Based on Negative Pressure in Flow Injection‐Capillary Electrophoresis System and Its Application to the Alkaline‐Earth Metal Cation Separation

Abstract

A new sample introduction method based on negative pressure has been developed in the flow injection (FI)–capillary electrophoresis (CE) system with contactless conductivity detection (CCD). In the system, the sample was carried to the interface by background electrolyte (BGE), which was carried by a dual‐channel peristaltic pump. Sample introduction into capillary was performed through the negative pressure at the outlet of capillary. Duration of the injection was controlled by a precise homemade time circuit connected to the voltage supply of vacuum pump. When the sample was transported to the inlet of capillary, the vacuum pump was started and a small volume sample was injected within 1.0–2.0 s. Negative pressures from 20 to 25 kPa are appropriate and other important injection parameters were studied. The RSD values (n=8) of the negatively pressurized injections, within the range of 0.8–1.1% for migration time, are comparable with those of gravity injection. The performance of the whole system was further demonstrated with satisfactory results in the separation of four alkaline–earth metal cations (Mg2+, Ca2+, Sr2+, Ba2+) with CCD. The project was supported by the National Natural Science Foundation of China (No. 20375049).