Design Of Contactless Conductivity Detection System For Capillary Electrophoresis Microchip

In the research of detection method and devices for capillary electrophoresis microchip, because of its simple structure and miniaturization, the electrochemical detection method has been a hot spot for scholars at home and abroad. Especially, capacitively coupled contactless conductivity detection has advantage of cotactless between electrode and solution, and it can detect many defferent materials, this method has broad prospects in capillary electrophoresis detection field. In the article, we’ll carry out the research of contactless conductivity detection for capillary electrophoresis microchip.In order to make the capillary electrophoresis microchips for contactless conductivity detection, a better equivalent circuit was put forwart. Afterwards, we simulate the relationship between detection cell structure parameters by MATLAB software, and design the capillary electrophoresis microchip’s structure of single and differential detection cell. Using the MEMS technique, we make the constituent part for capillary, including that glass-electrode substrate, PDMS insulating layer and micro-glass-channel cover plate.With the S3C6410processor of ARM11, we design the excitation source and detection circuit for the system. The detection circuit includes of preamplifier, lock-phase amplifier filter-rectifier and analog-to-digital, we use AD7888chip to collect data which has a SPI interface, and the excitation has voltage amplitude change between0to15V and frequency range from10kHz to400kHz. Linux drivers for AD7888, relay and digital potentiometer are developed. We also develop the application software for the system, which has the function of data saving and curve drawing, as well as control the circuit by their Linux drivers.We analysis the effection of parameters of detection cell to output signal with single detection cell, under the optimum experimental parameters, we detect different concentrations of potassium chloride solution, getting the lowest detection concentration of potassium icon is10-3mol/L. We also use the capillary electrophoresis microchip which has two detection cells to detect potassium chloride solution with the concentration of10-4mol/L, preliminary verified that differential detection can reduce the background noise.