The Application Of Three Laser-based Detection Methods In Separation-free System

Miniaturization is one of the new trends in analytical chemistry. Scientists felt obliged toinvestigate powerful micro-detection methods to meet the challenge from microchemicalanalysis. The miniaturization of instrument is limited by the size and capability of thedetection. The laser is an excellent tool for the analysis of small volume samples. In particular,the high spatial coherence of many contimuous wave lasers facilitates the production of highintensity beams which is necessary for the detection of small volume samples. Ideal microvolume detections possess high sensitivity and low limit of detection. Capillaryelectrophoresis （CE） and micro total analytical system （μ-TAS） also demand high efficiency,1-point and multifunctional detection. A novel1-point micro-detection system integrated withThermal lens （TL）, retro-reflected beam interference based RI （RBI） and laser-inducedfluorescence （LIF） was set up in this dissertation. And its application in separation-freedetermination of multiple components in matrixes was also discussed. We called it “photo-separation”. The following four parts were mainly discussed in this dissertation:1. Three laser-based micro-detection systems were set up individually in terms ofrelevant theories and technologies, which were co-axial TL, RBI and LIF. Each system wasoptimized.2. LIF and RBI were integrated into one micro-column, and a1-point bi-detectionsystem was set up. It was optimized by the adjustment of optics elements in order to reduceinteraction between LIF and RBI and improve its performance. The system was applied in theanalysis of erythrosine and sucrose binary solutions. In terms of separation-free, LIF focusedon the trace erythrosine and RBI monitored the high abundance sucrose in the solution. Withstandard binary solutions, calibrations of each method were set up. For fluorescent erythrosine,limit of detection （LOD） of0.03μg mL^-1（S/N=3） was achieved. For sucrose, limit ofdetection of refractive index change corresponding concentration change is0.39mg mL^-1wasachieved. Erythrosine and sucrose were “photo-separated” by bi-detection system. The retailmarshmallow candy was tested by the system. Erythrosine and sucrose in the candy wasquantified at the same time, single detection point and the same sample aliquot.3. Both TL and RBI were focused into a segment of capillary, and a1-point detectionsystem was set up. With the appropriate arrangement, RBI was added into dual beam co-axial TL. The configuration was optimized to decrease interaction. The binary solutions of sunsetyellow and sucrose were analyzed by the system without separation. TL monitored little sunsetyellow and RBI measured the main sucrose. With calibrations established by standardsolutions, sunset yellow and sucrose in retail soft drink were determined simultaneously andseparation-free. Limits of detection （LOD） of sucrose and sunset yellow were0.21mg mL^-1and0.23μg mL^-1.4. On the basis of former systems, a multi-functional detection system was set up by theintegration of LIF, TL and RBI. A fragment of capillary was set as micro cuvette for the1-point detection system. Each method was further optimized.“Photo-separation” of traceerythrosine, bit sunset yellow and mass sucrose was achieved. Tri-mixed standard solutionswere used to establish calibrations of each method. LOD of erythrosine, sunset yellow andsucrose were0.07μg mL^-1,1.6μg mL^-1and0.50mg mL^-1. The retail marshmallow floss wastested by the system, and erythrosine, sunset yellow and sucrose were all quantifiedsimultaneously without separation.