The Study Of C~4D Detector In Capillary Electrophoresis-Ion Chromatography

Capacitively coupled contactless conductivity detection (C4D) has gained increased significance in separation methods in the last years, particularly as a detection technique in capillary electrophoresis (CE) and ion chromatography (IC). Several review articles on C4D have been published summarizing applications of this detection method in different fields of analytical chemistry. The use of C4D for the CE determination of organic and biochemical species has been reported more frequently in the last several years. Based on capacitively coupling principle, two capacitively coupled contactless conductivity detectors (C4D) was constructed. Then the performance of the detectors is investigated by sample solution.According to the equivalent circuits or the detector, a C4D used in low pressure was designed. The effects of electrode length, gap between electrodes, excitation frequency and peak-to-peak voltage (Vpp) were studied. Best analysis conditions were concluded and the detection limits for K+ is 0.05μmol/L.Then the application of the detector is studied. Under optimized condition, five inorganic cations (K+,Ba2+,Na+,Mg2+,Li+) were determined in less than 5 minutes. The detection limits for these cations were 0.05,0.03,0.04,0.1,0.08μmol/L, respectively.A new C4D used in higher voltage was designed based on low voltage C4D. The detection cell, excitation signal generator and circuit were improved. The effects of electrode length, gap between electrodes, excitation frequency, peak-to-peak voltage (Vpp) and feedback resistor value were studied. In electrolyte solution consisting of 20 mmol/L MES/His the detection limits for K+ is 5×10-11mol/L under optimized condition.At last the application of the higher voltage C4D is evaluated in three conductivity buffer. Six inorganic cations were determined in less than 7 minutes, and the detection limits was as low as 10-8mol/L.