Rapid Detection Of Heavy Metal In Soil Of Gannan Navel Orange Plantation Land By Laser-induced Breakdown Spectroscopy

Navel orange is a kind of famous economic crop in Gannan district,but the contentof heavy metals in soil affects the quality of the naval orange directly,so the detection ofheavy metals in soil is very important. In order to introduce the laser induced breakdownspectroscopy(LIBS) to detect the heavy metal elements in the soil of navel orangeplantation land in Gannan district, and experimental analysis between the realconcentration and spectral intensity had been done on the soil samples which collectedfrom Gannan district；In order to enhance the intensity of spectrum of plasma emissionsignal, the author experimented on enhancing plasma emission signal and coaxial opticalpath DB-LIBS based on confinement of conical cavity;In order to improve the accuracyof LIBS when detecting heavy metal in the soil, the paper explored an experiment ofcombining iPLS method with LIBS technique.LIBS and AAS experiment have been done on soil samples from16differentregions in Xinfeng and Anxi county of Gannan. According to the comparison ofspectral intensity,signal to background ratio and real concentration of Cu and Cr in thedifferent area,the lowest concentration of Cu and Cr in the soil obtained from atomicabsorption experiment are3.179μg/g and6.524μg/g respectively, while their spectralintensities in the laser induced breakdown spectroscopy are both very distinct. And therelative standard deviation (RSD) in LIBS are all around10%.The CrI425.43nm was regarded as the research object in detecting national standardsoil. A conical cavity was installed below the focal length lens that next to the experimentsample which aims to confine the plasma emission signal in space and,to some extent,toconfine the plasma itself. Compared with the device of non-spatial confinement,thespectral intensity of Cr in the soil sample enhanced more than7%.Calibration curve wasestablished in the Cr concentration ranges from60μg/g to400μg/g. The liner regressioncoefficient and the limit of detection under the spatial confinement are better than thatwithout spatial confinement.In the experiment of coaxial optical path DB-LIBS, parameter optimization of thedelay time between two laser pulse and spectrum acquisition delay time was prioritized,and the spectrum information of Pb element at405.78nm was obtained. According to thecomprehensive comparison of spectrum intensity and signal to background ration, thebest laser pulse delay time and spectrum acquisition delay time are50ns and4.6μsrespectively. On this condition, the relative standard deviation reaches0.10. by thecomparison of the effect of double beam and single beam, a conclusion was made thatcharacteristic spectral intensity of Pb influenced by the double ones are strengthened2to3times.The paper proposed a method of quantitative analysis model based on iPLS. Targeting the line of Pb405.78nm, the selected spectrum was divided into25sub-intervals after the preprocess of data smoothly, the eighth subinterval contains thetarget spectrum line, and the Root Mean Square Error Cross-Validation (RMSECV) is theminimum.Then the quantitative model of the eighth subinterval was established.And thecorrelation coefficient of training set in iPLS model is0.9853, and the correlationcoefficient of predicting set is0.9858.