| High-performance capillary electrophoresis(HPCE)with small inject volume,high efficiency and short detection time.Compared with contact conductivity detector,Capacitively coupled contactless conductivity detector(C~4D)have a lot advantage.The structure of C4 D is simple.Electrodes of C4 D will not contact with solution,in this way,the electrodes can be used in a longer time.On the other hand,C4 D can be compared with tubes in different diameters.And C4 D can detect a lot of substances which without ultraviolet light group.For these resons,C4 D is used in different fields of analytical chemistry.Base on principles of capacitively coupling and differential detection,a C4 D with Wheatstone Bridge structure was constructed.Then the performance of the detectors is investigated by sample solution.The wheastone bridge structure is used to detect the tiny signal and decrease the baseline noise at the same time.The detection cell and electronic circuit are designed and made in the laboratory.Then,The effects of rectifying circuit,filter circuit,resistance values,peak-to-peak voltage(Vp-p),excitation frequency,electrode length,gap between electrodes were studied.Bridge rectifying circuit,RC filter circuit,5MΩ of resistance values,signal magnification 32 times,100Vp-p excitation voltage,100 kHz excitation frequency,1mm gap between electrodes and 3mm electrode length were choosed as the best conditions of the detector.At last the wheatstone bridge capillary electrophoresis capacitively coupled contactless conductivity differential detection system is applianced in detection of mixed solution sample and tube water sample.The effects of concentration of buffer solution,pH,additives are studied.Six inorganic cations were determined in less than 5 minutes,and the detection limit of K+ was as low as 10-9mol/L,the linear range is 10-9-10-7mol/L.The good resolution was achieved using 30 mmol/L MES/His+20 μmol/L CTAB buffer solution at pH=6.05,8kV separation voltage and 3s of electrophoretic injection. |
