Development Of Liquid Core Waveguide Enhanced Raman Spectrometer

As a commonly used on-site detection method,Raman spectroscopy is widely used in the fields of food,toxic substances,biochemistry,etc.due to its advantages of no loss,rapid detection,and large amount of information..However,the intensity of Raman scattering is very weak,and the relative intensity of its signal is usually only10^-1010^-4,which results in a weak signal and low sensitivity of the Raman spectrum,which limits its application range.Although scholars have discovered or studied a variety of Raman signal enhancement methods,such as Fourier transform-Raman?FT-Raman?,confocal micro-Raman spectroscopy?Laser Confocal Micro-Raman,LCM-Raman?,Surface-Enhanced Raman Scattering?SERS?and fiber-enhanced Raman spectroscopy.However,these methods have the problems of long detection time or complicated pre-processing,which is difficult to meet the needs of on-site detection.Liquid core waveguide technology?LCW?is a branching technique of fiber-enhanced Raman spectroscopy,which has the characteristics of low cost and small fluorescent background,but due to the inevitable problem of bubbles entering the detection environment and causing optical signal blockage during the detection process The stability and reproducibility of this technology are not very good.Based on the above,this chapter has developed a liquid-core waveguide enhanced Raman detector,which is divided into two types:negative pressure Raman spectrometer and positive pressure Raman spectrometer to improve the stability of the Raman spectrometer And reproducibility,and carried out related experiments and applications respectively.The research contents are as follows:?1?Built a negative pressure Raman spectrometerLiquid core waveguide technology,as a common means of analyzing Raman spectrum signals of liquid substances,has broad prospects in the field of Raman spectroscopy and even molecular spectroscopy due to its simple structure,fast analysis speed,and low sample loss.In practical applications,the detection object will inevitably carry a large amount of bubbles during the detection or directly generate a large number of bubbles directly into the liquid core waveguide,which directly affects the related spectral information such as the intensity and displacement of the Raman signal,which seriously affects the detection object Raman.Signal stability and reproducibility.Therefore,a negative pressure Raman spectrometer based on the liquid core waveguide technology was developed to enhance the Raman spectrum signal while removing bubbles in the detection substance,thereby obtaining a Raman detection signal with better stability and reproducibility.The system mainly includes:a)Raman laser,b)Raman spectrometer,c)Raman detection probe,d)solenoid valve,e)vacuum pump and f)detection module,the detection module is divided into conventional detection module and There are two types of 3D printing detection modules.After testing,it meets the needs of the experiment and provides hardware support for subsequent experiments.?2?A positive pressure Raman spectrometer was builtIn order to pursue a greater pressure value,a positive pressure Raman detection spectrometer was built.At the same time,the integrity of the detection instrument was pursued,and a simple instrument operation method was provided to speed up the experiment efficiency and improve the user experience.The system mainly includes:a)Raman laser,b)Raman spectrometer,c)Raman detection probe,d)computer and e)detection module.At the same time,the corresponding PLC control program has been written.After testing,it meets the experiment Requirements,to provide hardware support for subsequent experiments.?3?Experiment and application of liquid core waveguide enhanced Raman spectrometerIn the experiment and application work,the model of the liquid core waveguide was determined.Finally,the diameter of the liquid core waveguide was determined to be 0.009 inches?229?m?inside diameter,0.016 inches?406?m?outside diameter,and 0.005 inches wall thickness?177?m?,and determine the length of 20 cm.At the same time,the relevant parameters of the negative pressure Raman spectrometer and positive pressure Raman spectrometer were optimized respectively.The detection limits of the two instruments for alcohol were 0.03%and 0.02%?v:v?,respectively,and the linear correlation coefficient They are 0.999 and 0.9998 respectively,and the stability and reproducibility of the two instruments are evaluated respectively.The RSD of the stability and reproducibility of the negative pressure Raman spectrometer are 3%and 4%,respectively.The stability and reproducibility RSD of the Mann detector is 2%and 5%,respectively.The application experiment of negative pressure Raman spectrometer was conducted using potassium sorbate,and the detection limit was calculated to be 0.05 g/kg with a linearity of 0.9989.After that,the concentration of sorbic acid was lowered by freeze enrichment The potassium solution was tested,and the detection limit was calculated to be 0.005 g/kg and the linearity was 0.9908.The RSD of the stability and reproducibility of potassium sorbate was 3%and 4%,respectively.For the positive pressure Raman spectrometer,the hydrogen peroxide solution was measured,and the detection limit was calculated to be 0.02%?v:v?,the linearity was 0.997,and the RSD of the stability and reproducibility of hydrogen peroxide were obtained by experiment 7%and 9%.