Laser-induced Breakdown Spectroscopy Of Metal Elements In Aqueous Solutions

Laser-induced breakdown spectroscopy(LIBS)is a good spectral technology for elemental analysis from optical emission signal generated by pulsed laser ablation of samples.The optical signal emitted from plasma contains the spectral characteristics of elements in samples.After decades of development,LIBS has become a fast and convenient spectral analysis technique,and has been successfully applied to a variety of fields.Compared with other spectral analysis techniques,LIBS has many unique advantages,including weaker sample preparation or no sample preparation;multi-element measurement;less damage to sample;it can realize real-time,fast and fixed-point analysis;and capable of remote detection,etc.Therefore,LIBS has good application prospects in the fields of environmental monitoring,industrial analysis,geological application,biomedical identification,agriculture,archaeology,and space exploration,etc.However,LIBS has some disadvantages for the analysis of liquid samples.The problems such as droplet splash,fluctuation,and plasma quenching seriously affect the sensitivity and accuracy for LIBS detection of liquid samples.How to improve the LIBS analysis sensitivity of metal elements in aqueous solutions has become an urgent problem to be solved.Therefore,based on the traditional liquid jet method and surface enhanced LIBS(SE-LIBS)method,this paper selected metal elements(Na,Pb,and Cr elements)as the research object.By optimizing the injection mode of liquid samples and adjusting the experimental conditions,the spectral intensity of trace metal elements in the solution was improved,so as to improve the detection sensitivity of LIBS technology for the analysis of liquid samples.The specific research contents are as follows:1.Femtosecond laser is used to breakdown the water film to detect Na Cl aqueous solutions.The injection mode of liquid sample is transformed into water film,which provides a stable liquid surface for laser focus and overcomes the disadvantage that the laser focus position cannot be fixed due to liquid fluctuation.In addition,femtosecond pulsed laser is used to generate plasma,which effectively avoids the splashing of liquid.The calibration curve of Na element is plotted by measuring Na Cl solutions with different concentrations,and the relative standard deviation is calculated.It shows that the combination of femtosecond laser and water film can significantly improve the spectral measurement stability of liquid samples analyzed by LIBS.2.Based on the femtosecond laser breakdown of water film,the effect of lens focus position on the spectral intensity of Na plasma in aqueous solution is studied.The quantitative analysis of Na element with different concentrations is carried out.The detection limit and relative standard deviation of Na element are calculated through the calibration curve of Na element.It is confirmed that selecting the best lens focus position can further improve the analytical performance of femtosecond LIBS for aqueous solution.3.The effect of substrate temperature on the spectra of heavy metals in aqueous solution detected by SE-LIBS is discussed.By establishing the calibration curve of Pb and Cr at different substrate temperatures,the corresponding element detection limits are calculated.The result shows that increasing the substrate temperature can significantly improve the detection sensitivity of SE-LIBS for the detection of heavy metals.4.The effect of gold nanoparticles on the SE-LIBS of heavy metals in aqueous solution are investigated.The deposition of standard solution containing gold nanoparticles on metal Al substrate significantly reduces the breakdown threshold and enhances the spectral intensity.The calibration curves of Pb and Cr,and calculated the detection limits,show that the combination of nanoparticles and SE-LIBS can remarkably improve the detection sensitivity of SE-LIBS technology.In conclusion,the detection methods of femtosecond laser-induced water film,substrate temperature enhanced SE-LIBS,and other liquid samples are studied.It has significantly improved the characteristic spectral intensity,detection sensitivity,and stability of metal elements in aqueous solutions,and the results enable LIBS technology to be better applied to the analysis and detection of heavy metals in liquid samples.The studies provide good ideas for the detection of heavy metals in aqueous solutions.