Development And Application Of A Variable Wavelength Laser Induced Fluorescence Detector

Fluorescnce detector(FLD)has the advantage of high sensitivity,otherwise laser induced fluorescnce(LIF)is the higher sensitivity technology which is using a strong monochromatic laser as light source.So the limit of detection of LIF detector is 1×10~-1212 mol/L.Although the LIF technology has a high sensitivity,it is difficult to design the optical path.So the majority of the related studies of LIF are in the laboratory stage and have poor stability.In addition,LIF detector only can stimulate the fluorescent materials which have corresponding excitation wavelength.Due to the laser just have single wavelength,it resulted in a narrow range of LIF applications.The aim of this study is to independent develop of excellent and powerful variable wavelength laser induced fluorescence detector,which was designed to solve the problem of poor stability and narrow application of recent LIF detector,by using laser optical fiber technique and modular design concept.And we also combinied LIF with pressurized capillary electrochromatography(pCEC)to detect four aflatoxins.The pCEC-LIF have the advantages of high selectivity,high resolution and high sensitivity.A fast and efficient analysis method for determination of four aflatoxins was developed by using pCEC-LIF.This thesis contains five chapters as follows:The first chapter briefly introduced the research progress,application advantages and the basic theory of laser induced fluorescence technology.Chapter two specifiied introduced the mechanical structure design of the instrument.The structure design contained four parts,including the laser,the detection pool,the main body of the optical path and the peripheral structure.These parts were designed to achieve the high sensitivity,good stability and excellent performance.Also simple and fast wavelength changed between different wavelengths should be available.In chapter three,the design of the circuit was introduced in detail.Main contents in this parts were the selection of the PMT(Photomultiplier tube).To make sure that PMT had outstanding performance,we designed filter module to reduce noise of power supply and processed continuously adjustable function for signal gain.Moreover we also used powerful A/D converter and chromatography acquisition software to improve equipment performance.In chapter four,we set the performance indexes and described the methods for detecting four wavelength.The testing result of four wavelength fitted performance indexes very well.In the fifth chapter,pCEC-LIF was established and applied to determine four aflatoxins.Various factors affecting the separation were investigated and the optimum separation conditions were decided.The methods of the separation and detection by using the pCEC-LIF detector can realize detection of trace amounts of aflatoxins.