Nondestructive Determination of Cu Residue in Orange Peel by Laser Induced Breakdown Spectroscopy

Laser induced breakdown spectroscopy (LIBS) is an emerging tool with rapid, nonde?structive, green characteristics in qualitative or quantitative analyses of composition in materials. But LIBS has its shortcomings in detect limit and sensitivity. In this work, heavy metal Cu in Gannan Navel Orange, which is one of famous fruits from Jiangxi of China, was analyzed. In view of LIBS’s limit, it is difficult to determinate heavy metals in natural fruits. In this work, nine orange samples were pretreated in 50-500 μg/mL Cu solution, respectively. Another one orange sample was chosen as a control group without any pollution treatment. Previous researchers ob-served that the content of heavy metals is much higher in peel than in pulp. So, the content in pulp can be reflected by detecting peel. The real concentrations of Cu in peels were acquired by atomic absorption spectrophotometer (AAS). A calibration model of Cu I 324.7 and Cu I 327.4 was constructed between LIBS intensity and AAS concentration by six samples. The correlation coefficient of the two models is also 0.95. All of the samples were used to verify the accuracy of the model. The results show that the relative error (RE) between predicted and real concentration is less than 6.5%, and Cu I 324.7 line has smaller RE than Cu I 327.4. The analysis demonstrated that different characteristic lines decided different accuracy. The results prove the feasibility of detecting heavy metals in fruits by LIBS. But the results are limited in treated samples. The next work will focus on direct analysis of heavy metals in natural fruits without any pretreatment. This work is helpful to explore the distribution of heavy metals between pulp and peel.