Detection Of Heavy Metal Elements In Solution With Laser-induced Breakdown Spectroscopy

Laser-induced breakdown soectroscopy(LIBS)technology, as an emmission spectroscopy technology, can be used in qualitative and quantitative analysis for different elements. In LIBS process, a high energy density laser is focused on the sample, then high temperature plasma will be induced, atom and ion lines will be recorded when plasma compositely cools down.LIBS is under a fast development and attracts lots of attentions as LIBS is a in-time, quick, remote, no sample preparation, multi-element simultaneous chemical analysis method that can be applied in many areas, such as medicine, archaeology, biotechnology, online industrial measurement. LIBS can be used in detection of solid,liquid and gas.In liquid detection, lots of problems need to be solved, for example,weak signal intensity, bad stability and fast plasma quenching. This thesis aims to improve LIBS intensity and detection of heavy metals in solution. In practical terms,two LIBS methods, printing paper as solid absorption base and double-pulse LIBS(DP-LIBS), will be researched in this thesis to get a better signal intensity and sensitivity in solution.Based on the problems LIBS used in metal elements detection in liquid, double pulse(DP) Laser-induced Breakdown Spectroscopy(LIBS) has been used for the detection of Cu in solution. Two nanosecond scale Nd:YAG lasers at1064nm are combined in collinear beam geometry to carry out the DP-LIBS experiments. Firstly, we put this system in detection of aluminium alloy. Spectral lines of trace elements like Si, Cu, Mn, Cr from the standard samples are greatly enhanced (9-17times) within a8μs time delay between the two pulses, relative to single-pulse LIBS with same total energy. In the end, LOD(limit of detection) of Si, Cu, Mn, Cr are given to be3-171mg/L, where LOD of trace metals reach the order1-10ppm, indicating DP-LIBS a powerful instrument of trace,elements detection in aluminium alloy. After that, DP-LIBS is applied in statistic liquid. Focusing and spectral acquisition system has been improved to meet the need of liquid detection. Spectra intensity change with different ratio of energy of two pulses. Time delay between two pulses and position of focus point has been optimized. In the end, calibration of Cu in solution is acquired, and LOD of Cu is found to be2.0mg/L, which is better than traditional LIBS detecting results, reaching the same level of LOD of other LIBS methods.In addition, this paper puts forward a method that printing paper is used as solid absorption base to aborb metal elements in solution,then conventional LIBS is used on the printing paper.From experimental observation,strong and stable spectra signal of Cr and Pb have been aquired.We analyze the spectra data in detail, study the relationship between signal intensity and soaking time,and find limit of detection(LOD) of Cr and Pb reach the order of10ppb,which has significant improvement than LIBS directly used in liquid and other LIBS methods. All works are summarized at the end of this thesis to make the idea of the future works.