Rapid And Highly Sensitive Analysis Of Trace Elements In Chinese Herbs And Copper Alloy Samples Based On Laser-induced Plasma Spectroscopy

The quantitative analysis of material elements is of great significance in physics,chemistry,material,biological,pharmaceutical,environmental sciences,and industrial and agricultural production,and it is necessary to help understand the composition,structure,and properties of the samples.Conventional material elemental analysis techniques,such as atomic absorption spectroscopy(AAS),inductively coupled plasma optical emission spectroscopy or mass spectrometry(ICP-OES/MS),need to digest solid samples before analysis.This is more time-consuming,thus reducing the analytical speed.Laser-induced breakdown spectroscopy(LIBS)has attracted much attention because it can directly analyze solid samples.However,the spectral analytical sensitivity of LIBS is lower than that of conventional analytical techniques due to the limitation of the characteristics of laser interaction with matter.In order to improve the spectral analysis sensitivity of LIBS,different techniques have been studied to enhance the plasma emissions.In addition,in order to establish a portable spectral analysis system and improve the analytical speed,Lasers operated under high repetition rate have been used as excitation laser sources to carry out elemental analysis with LIBS.In this thesis,two LIBS-related spectral analysis techniques were studied.First,LIBS combined with laser-induced fluorescence(LIF)(LIBS-LIF)was used to realize direct and highly sensitive analysis of toxic heavy metal,lead in medicinal plants.Second,trace elements in copper alloys were rapidly analyzed with high repetition rate laser-ablation spark-induced breakdown spectroscopy(HRR LA-SIBS).The analytical sensitivities of these two techniques have also been evaluated.The toxic heavy metals in medicinal plants are potentially harmful to human health;therefore,the concentrations of toxic heavy metals in medicinal plants are strictly regulated in the world.In order to develop a direct and highly sensitive spectral analytical technique for analyzing trace toxic heavy metals in medicinal plants,the LIBS-LIF technique was used to quantitatively analyze trace lead in Chinese herbal plant Rheum officinale.To overcome the problems due to differences in size,shape and density of different samples,the original samples were ground into powder and then pressed into pellets for spectral analysis.A calibration curve of lead in Rheum officinale was established by LIBS-LIF based on self-made standard samples.The linear correlation coefficient R~2 of the calibration reached0.996 and the detection limit of lead was 0.13 ppm,satisfying the requirement of highly sensitive analysis of trace lead in medicinal plants.In comparison with LIBS analysis,the enhancement factor of signal-to-background ratio in LIBS-LIF was more than 2 orders at low lead concentration.The concentrations of lead in several original Rheum officinale samples were also analyzed with this technique,and it was found that the concentration of lead in these samples did not exceed the standard.This work demonstrates that LIBS-LIF can be successfully applied to the highly sensitive and rapid analysis of toxic heavy metals in medicinal plants.In this thesis,a fiber laser was used as an ablation laser source and the trace elements in copper alloy samples have been quantitatively analyzed with HRR LA-SIBS technique for the first time.Operated under 30 k Hz repetition rate,the characteristics of spark discharge and the effect of discharge voltage and energy storage capacitance on the signal intensity and signal-to-background ratio for different atomic lines were investigated.By selecting Pb I368.35 nm,Fe I 358.12 nm and Al I 396.15 nm analytical lines,and recording the spectra with a portable fiber spectrometer,the lead,iron and aluminum elements in the copper alloy samples were quantitatively analyzed.Under the condition of 0.6 m J laser pulse energy,the detection limits of lead,iron and aluminum in the copper alloy obtained by LIBS analysis were 1309,1022 and 106 ppm,respectively.However,under the assistance of the spark discharge,that is to say,in HRR LA-SIBS analysis,the detection limits of them have been improved to 240,113 and 30 ppm,respectively.The improvement factor was 3-9 folds.This work demonstrates that spark discharge can improve the analytical sensitivity of a portable high repetition rate LIBS system containing a fiber laser and fiber spectrometer.The HRR LA-SIBS based on fiber laser and fiber spectrometer can be used for rapid and sensitive elemental analysis of alloy samples,and it is deserved to extend its application in metallurgical fields.