Quantitative analysis of Pb in kelp samples and offshore seawater by laser-induced breakdown spectroscopy

Abstract

In this study, laser-induced breakdown spectroscopy (LIBS) was applied for the qualitative elemental analysis of kelp. The spectrum of the uncontaminated kelp indicated that kelp contains elements of Fe, Na, Ca, Cr, Mn, Zn, and Pb. Then, nine Pb solutions with different Pb concentrations were prepared to simulate contaminated offshore seawater and kelp samples were dipped into these solutions. The spectra of these contaminated kelp samples were obtained using the LIBS technique. It is worth mentioning that in order to accurately identify the spectral lines of Pb in the spectrum, the spectrum of pure Pb was selected as the reference spectrum and the spectral lines of Pb (357.272 nm, 363.956 nm, 368.346 nm, 373.993 nm and 405.781 nm) were determined. Taking Fe (589.117 nm) as the reference spectral line, the relative intensity of these five spectral lines of Pb were summed up as the relative intensity of Pb and the calibration curve for Pb was obtained by an internal standard method. The linear correlation coefficients (R2) for the linear fitting of the relative intensity versus the concentration of Pb is 0.986 31. Furthermore, kelp samples with approximately 1 ppm and 10 ppm Pb were prepared to test the accuracy of LIBS in slightly contaminated offshore seawater. Comparing these spectra with the spectrum of uncontaminated kelp, it is found that the limit of detection for the LIBS technique is between 1 ppm and 10 ppm. The results of the experiments showed that the application of the LIBS technique to kelp in seawater is a promising way to determine the concentration of Pb in contaminated offshore seawater.