Detection and quantification of Pb and Cr in oysters using laser-induced breakdown spectroscopy

The quantitative determination of heavy metals in aquatic products is of great importance for food security issues. Laser-induced breakdown spectroscopy (LIBS) has been used in a variety of foodstuff analysis, but is still limited by its low sensitivity when targeting trace heavy metals. In this work, we compare three sample enrichment methods, namely drying, carbonization, and ashing, for increasing detection sensitivity by LIBS analysis for Pb and Cr in oyster samples. The results demonstrate that carbonization can remove a significant amount of the contributions of organic elements C, H, N and O; meanwhile, the signals of the metallic elements such as Cu, Pb, Sr, Ca, Cr and Mg are enhanced by 3–6 times after carbonization, and further enhanced by 5–9 times after ashing. Such enhancement is not only due to the more concentrated metallic elements in the sample compared to the dried ones, but also the unifying of the matter in carbonized and ashed samples from which higher plasma temperature and electron density are observed. This condition favors the detection of trace elements. According to the calibration curves with univariate and multivariate analysis, the ashing method is considered to be the best choice. The limits of detection of the ashing method are 0.52 mg kg⁻¹ for Pb and 0.08 mg kg⁻¹ for Cr, which can detect the presence of heavy metals in the oysters exceeding the maximum limits of Pb and Cr required by the Chinese national standard. This method provides a promising application for the heavy metal contamination monitoring in the aquatic product industry.