Detection Of Metal Elements In Chinese Herbal Medicine Based On Re-heating Double-pulse LIBS

Laser-induced breakdown spectroscopy?LIBS?technology was widely used in the detection and analysis of substances,with the advantages of simultaneous detection of multiple elements,no need for complex sample pretreatment,and real-time rapid detection in the field.The content of microelements in Chinese herbal medicines has great relations with its efficacy.However,the heavy metal pollution in Chinese herbal medicines will seriously impair the health of patients.Therefore,the rapid analysis of the heavy metal elements in Chinese herbal medicines is essential to control the quality of Chinese herbal medicines.Single-pulse laser-induced breakdown spectroscopy?SP-LIBS?technology has low detection sensitivity and poor stability in the detection and analysis of Chinese herbal medicines,therefore,a detection method based on re-heating double pulse laser-induced breakdown spectroscopy?RDP-LIBS?was proposed in this thesis,which is used for metal elements detection in Chinese herbal medicines.The main research contents include the following:In this thesis,a re-heating double pulse laser-induced breakdown spectroscopy system was set up.Its working principle is that the sample surface was excited by the first laser vertically to generate the plasm.A certain time was delayed by the digital pulse delay generator.After that,the plasma was reheated by the second laser,and then the spectrum signal radiated by the plasma was detected by the spectrometer.The experimental parameters including detection delay,laser energy and pulse interval time were optimized.The results showed that optimized detection delay and pulse interval time were 1.5?s and 4.4?s,respectively,and the main pulse laser energy was 15 mJ,the re-heating pulse laser energy was 35 mJ.With the optimized experimental parameters,the enhancement of the emission spectral intensity of Fe,Al,Ca,CN,etc.and plasma electron excitation temperature and electron number density of Coptis chinensis were studied.The results showed that the spectral enhancement of the four characteristic lines Fe I?358.17 nm?,Al I?396.15 nm?,Ca II?393.37 nm?and CN?388.34 nm?were 4.0,3.5,10.0 and 5.5,respectively.The plasma electron excitation temperature had a 937 K increase and the electron density had a 0.91×10¹⁶ cm^-3increase.The mechanism of line enhancement of RDP-LIBS technology was discussed and the feasibility of RDP-LIBS technology for the detection of Chinese herbal medicine samples was verified.Finally,the RDP-LIBS technology was used to detect the heavy metal element of Cu and Pb in Coptis chinensis and Artemisia annua L.Compared with SP-LIBS technology,the limits of detection Cu and Pb in Coptis chinensis were reduced by about2.7-fold and 3.4-fold,respectively.The limits of detection Cu and Pb in Artemisia annua L were reduced by about 2.9-fold and 3.1-fold,respectively.With RDP-LIBS technology,the linearity of Cu and Pb elements calibration curve were more than 0.98,which showed a considerable linear correlation,indicating that it can improve the detection sensitivity of LIBS technology and reduce the limits of detection heavy metal elements in Chinese herbal medicines.