| Elemental analysis based on the emission spectrum from the plasma generated by focusing a high power density laser beam on the sample surface is known as Laser-Induced Breakdown Spectroscopy (LIBS) generated along with the emergence of laser. When the sample surface irradiated by enough high power density laser beam, it will be vaporized and then the neutral and ionic species are formed at excited states. The emission spectra from the excited species can be used to confirm the sample composition and the trace concentration quantitatively. So this new technique can be used to detect the trace elements contained in solid, gaseous and liquid matrix. Because of the potential advantages possessed by this technique as rapid detection, the least destroying of the samples, on-line and in situ analysis, remote field exploration, and some special characteristics such as applicable in high temperature and hostile environment where can't be reached by traditional chemical analysis methods, LIBS technique will be used extensively in the fields as material science, chemistry, environment, medicine, archaeology, metallurgy and so on.LIBS technique has been successfully employed for qualitative and semi-quantitative elemental analysis in solid and gaseous samples so far. But for liquid sample, due to the influences of the unstable factors as shock wave, splashing, and light absorption produced by the interaction between the sample and ablation laser, the application LIBS for liquid sample is situated in laboratory studying step. There are many key problems in theory and experimental technique should be resolved for practical application. In this paper, we studied the LIBS of the liquid sample in experiment. The LIBS spectra of Cu and Pb in CuSO4 and Pb(NO3)2 aqueous solution were measured respectively and its time evolution properties were also investigated. Through the measurement of intensity ratios (S/B) between the spectral lines and continuous background radiation at different time delay and different laser power density, the optimum experimental conditions were obtained. Under the optimum condition we measured the LIBS calibration curves for Cu and Pb in the two solutions and obtained the LIBS detection limits for the two elements respectively. The conclusions obtained from the experiment will provide valuable experimental and technical parameters for the field detection of the heavy metal pollution in ocean. This paper is parted into six chapters and the main content are listed as following.The characteristics and the development of LIBS were introduced in detail in the first chapter. Due to contact relation between LIBS and laser induced plasmas, the basic principles of laser-induced plasma and LIBS, as well as the plasma diagnostic method by emission spectra were reviewed in chapter 2.The experimental setup and the measurement method were described in chapter 3 in detail. The work theory and the technical parameters of the apparatus involved in this experiment were depicted briefly.In Chapter 4 and 5, the experimental study on the Laser-induced Breakdown Spectroscopy of the CuSO4 and Pb(NO3)2 aqueous solution was presented. The time evolution properties of the Cu and Pb LIBS signal and the dependence of the LIBS signal on the laser power density were studied by single pulse laser. Under the optimum experimental condition, both of the LIBS calibration curves of Cu and Pb elements were measured and the detection limit with the values 23ppm and 177 ppm for Cu and Pb respectively were obtained from the fitting of the calibration curves. It was shown from the experiment results :(1)Both the intensities of discrete spectra and continuous radiations from the plasma emission experienced the process of increasing followed by decreasing along with the time delay, but the increasing and decreasing speeds of the discrete spectral intensity were larger than that of the continuous radiations. (2) The optimum experimental conditions were obtained. The time delay is about 700ns and 800ns and the suitable ablation laser energy is 40 mJ and 35mJ for the solution of CuSO4 and Pb(NO3)2 respectively. The ablation laser energy used in our experiment is lower than that reported in previous experiments, but a higher detection limit was obtained with single laser pulse.In the last part of this thesis, we put forward some key problems be solved in future for application of LIBS in quantitative trace element analysis in liquid matrix based on the summarization of our experiment results and some considerations on the next research were also presented.
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