UV-VIS Spectroscopic Sensing System For Solution Concentration Detection

With the fast development of modern industry, a growing number of industrial waste containing toxic and harmful components may do great harm to human health. Using fiber optic technology, the development of sensing system for detecting the concentration of polluted solutions is of great value in application. The systems should be small, portable, accurate and reliable with online real-time continuous monitoring ability.Hollow fiber has found applications in infrared laser power delivery and gas sensing, due to its high damage threshold, no end reflection loss, good flexibility, etc. In this paper, metallic hollow fiber is used in spectroscopic sensing system for aqueous solutions owing to its unique structure of hollow core and low-loss property in ultraviolet-visible wavelength regions. A stable and practical sensing system is established for detecting the concentration of solutions based on UV-VIS spectroscopic absorption. A theoretical model of liquid absorption in metallic hollow fiber is proposed, and the influence of system parameters on sensing performance is accordingly analyzed. There exists an optimum length of hollow fiber which insures the system the highest sensitivity in detection. And high SNR enlarges the linear measuring range of the detection system.Two silver-coated hollow fibers with inner diameter of 700μm were used as the absorption cell. They were 6.4cm and 8cm long, respectively. Experiments on measuring C0Cl2 and Na2SO4 aqueous solutions were conducted respectively with these two fibers. Two absorption peaks were observed respectively, the wavelength band of 510nm for C0Cl2,372nm for Na2SO4. The absorption shows good linear relationship with the concentrations which fitted the simulation well and proved the system as useful and practical. The system was also tested and analyzed. The experimental results show that the system is stable, reliable and accurate with high sensitivity and has the advantages of rapid response and easy operation. The possibilities of miniaturization and on-line measurement make the system a potential candidate for promising application in the environment monitoring, chemical process control, and medicine fabrication processing.