毛细管电泳-电容耦合非接触式电导检测方法在低频率激励下的性能优化OA

The capillary Electrophoresis-capacitively coupled contactless conductivity detection(CE-C4D)method offers many advantages such as small sample volume,high throughput,simultaneous detection of cations and anions,fast analysis speed,and easy miniaturization of instruments.With the continuous improvement of its own sensitivity,the development of CE-C4D instruments featuring both high sensitivity and miniaturization is crucial for the further promotion of this method.Capacitance-to-digital converter(CDC)detection technology is highly conducive to the miniaturization of C4D instruments,as it can realize functions including output of excitation waveform,capacitance acquisition,24-bit analog-to-digital conversion,and digital signal transmission through a single chip.However,this technique operates under low-frequency excitation(30 kHz,excitation voltage of 3.3 V with fixed parameters),which is significantly different from the traditional 100-kHz or MHz-level excitation frequencies.To conduct an in-depth study on the influencing factors of C4D signals,separation efficiency and method detection limit under low-frequency excitation,this work started from the equivalent circuit model of C4D and adopted a conductivity measurement model based on differential detection to systematically investigate the effects of electrode length,excitation frequency,and electronic circuits on CE-C4D signals and resolution.It was found that as the excitation frequency decreased from 1 MHz to 30 kHz,the half-peak width of the Li+electrophoretic chromatogram significantly broadened,approximately from 1.24 s to 3.36 s.This phenomenon was speculated to be caused by the increased effective detection interval under low frequencies,but peak broadening was unfavorable for improving electrophoretic separation efficiency.Based on this low-frequency characteristic(i.e.,low effective bandwidth),the method detection limit of CE-C4D technology under low-frequency excitation was optimized and improved for the first time by increasing the excitation voltage and circuit gain,achieving a detection limit of 100 nmol/L for Li+samples.Through model analysis and experimental research,this work further broadened the understanding of the signal response characteristics of CE-C4D technology under low excitation frequencies.