A Dynamic Study On The Laser-induced Breakdown Spectroscopy Of Trace Metallic Elements In Aqueous Solutions

Laser-induced breakdown spectroscopy is a new kind of spectral analysis method,which does not require complex pretreatment to the sample.Compared with traditional detection method,it has the peculiar advantages of being real-time,fast,online,remote detection,small destructive of sample and multi-elements detection.Therefore,the application fields of it are already very broad.However,the sensitivity and accuracy are not very high when using this technology to the detection of aqueous solution,and the experimental results are often affected by the matrix effect.So,LIBS for liquid phase is still in the stage of development.In order to solve this problem,the liquid jet sampling technique is adopted in this paper;the analysis lines of seven metal elements mixed in the aqueous solution,such as Pb,Cr,Cd,Mn,Ca,Al,and Co are selected to optimize the key experiment parameters.when the laser plasma obtained in this case are satisfied with the local thermal equilibrium and optical thin conditions,the kinetic characteristics of it are studied systematically.Based on the plasma characteristics,a calibration-free quantitative analysis method is established in order to overcome the matrix effect.The specific research content is as follows:The formation and evolution dynamics of laser-induced plasma are investigated.It has been judged from previous work that laser pulse energy,ICCD gate delay and sample flow rate are the key experiment parameters to affect the formation and evolution dynamics of plasma.According to the variation trend of spectral intensity and the maximum principle of signal-to-noise ratio,the values of the above three parameters under the optimal experimental conditions are determined to be 50mJ and2.0?s and 40mL/min,respectively.Under the condition of optimized experiment parameters,the characteristics of plasma are studied deeply,and the electron temperature and electron number density are obtained to be 4393K and 5.1?10 ¹²cm^-3.On this basis,it is verified that the plasma are satisfied with the local thermal equilibrium and optical thin conditions in a specific time window.Then,according to the integral intensity of emission lines from the experiment and the time-resolved imaging information of plasma,the variation trends of the electron temperature and electron number density with the key experiment parameters,such as laser pulse energy,ICCD gate delay,and liquid sample flow rate,are obtained when using the same method.This provides an important reference value for the dynamics research of LIBS in the field of liquid phase.An approach of quantitative analysis method of trace metal elements which can overcome matrix effect is presented.The new quantitative analysis method,based on the plasma characteristics,is improved form the CF-LIBS and programmed by Matlab.The absolute concentration of each element is determined by the calculated electron temperature,electron number density and the ratio of the particle density of the same element and the adjacent ionization state of different elements.The results show that the experimental values are in good agreement with the calculated one,and the relative errors of analytical elements,which account for a large content in the sample solution,are less than 5%.Subsequently,the matrix effect is verified.Regarding Mn and Al as the matrix,the concentration is magnified to dozens of times of the original to detect the absolute content of Cr.The results show that the content of Cr obtained from the two tests are almost equal,which prove that the quantitative analysis method could overcome the matrix effect and is an effective method for the determination of liquid without standard samples.It will be possible to apply this method to the rapid and on-line analysis of industrial wastewater.