Detection of lead chrome green in Tieguanyin tea by laser-induced breakdown spectroscopy

Abstract

In this work, laser-induced breakdown spectroscopy (LIBS) was used to analyse the elemental composition of Tieguanyin tea and lead chrome green (LCG). It was found that Fe, Ca and Mg were contained in both LCG and tea, and Cr, Pb and Cu were unique to LCG, while elements such as Na, K, Al, Si, Mn and Sr were unique to tea. In addition, the free radicals of CN, CaO and C₂ in LIBS spectra of tea and tea with LCG (LCG–tea) samples were studied. Moreover, the differences of spectral line intensities of Pb atoms and CN free radicals were used to qualitatively detect LCG illegally added in tea. Finally, the principal component analysis (PCA) was carried out by using CN and CaO spectral lines, which could well distinguish ordinary tea from LCG-tea. Compared with PCA results using all atomic and ionic spectral lines, the cumulative contribution rate of the two PCs increased from 90.7% to 99.4%.