Experimental Study Of Heavy Metals In Fresh Orange Leaves By Laser-induced Breakdown Spectroscopy

In recent years, along with the rapid economic development, environmental pollutionproblem is increasingly serious. Among them, the heavy metal pollution directly affects thequality and safety of agricultural products, has aroused extensive attention. Therefore,real-time monitoring of heavy metal pollution is of great significance. The conventionaldetection methods of heavy metals in agricultural products are complex processing,time-consuming, reagent consumption and easy to cause secondary pollution.Laser-induced breakdown spectroscopy （LIBS） is an effective tool to quantitative analyzethe material elements rapidly. The technique requires no preprocessing, simple operation,with real-time, rapid and nondestructive, in situ detection and other characteristics. Theapplication of heavy metals detection in agricultural products has broad prospects.Takingthree heavy metals （Cr, Cu, Pb） of fresh orange leaves as the research object, a new methodof using single pulse ns-LIBS present. The main research contents are as follows.Firstly, the LIBS detection system set up. According to the experimental requirements,the test device were optimize, expand the DG535digital pulse delay unit and laser energymeter, and to improve the light collection system.Secondly, the LIBS parameters were optimized. The influence of laser pulse energy,time delay and frequency spectrum on LIBS characteristic spectral lines of elements wasanalyzed. Evaluating the signal-to-background ratio and spectral intensity, the optimizationof laser pulses energy and delay time are obtained. Evaluating the signal-to-backgroundratio and relative standard deviation, the best value of repetition frequency get.Next, samples of fresh orange were prepared. The orang leaves from ecological park inJiangxi Agricultural University, soaked in heavy metal solution. After48hours, took outand dried in the air. In order to ensure the formation of the sample surface and reduce themeasurement error, leaves stuck on the smooth plastic plate using double-sided adhesive.Finally, quantitative analysis was done. Under the optimum experimental conditions, theLIBS spectra of fresh orange leaf was measured. Reference the selection rules ofcharacteristic spectral lines of elements, the reasonable analytical spectral lines werescreened, CrI425.44nm, CuI324.75nm and PbI405.78nm. Real content of elements weremeasured by flame atomic absorption spectrometry. The quantitative analysis models ofelements Cr, Cu and Pb were set up by logarithmic method, the strength ratio and siPLSrespectively, a correlation of0.99,0.99and0.9579, and the detection limit of Cr and Cuwas12.01ug·g^-1and10.81ug·g^-1. Using12samples to verify the linear model of Cu, therelative error is0.97%².92%. And more, the R value of siPLS validation group of Pb is0.9213, the RMSEP value was100.In conclusion, these research suggest that LIBS technology has certain developmentpotential in the quantitative analysis of orange leaves. The optimization of the sensitivity,stability and the detection limit will research in last work.