Study On Novel Laser Induced Breakdown Spectroscopy Methods For Detection Of Heavy Metals In Cosmetics

Cosmetics play an important role in daily necessity that contacts with human body directly,whose quality and safety have been frequently exposed.In particular,the excessive heavy metals present a safety challenge.However,there are disadvantages in the traditional detection method of heavy metals,such as long detection period,complex sample processing procedures,and low detection efficiency,which makes it hard to adapt to the current severe situation of cosmetics safety.Therefore,it is urgent to develop novel and efficient techniques of heavy metals detection for cosmetics.Typical heavy metals in polymorphic cosmetics were detected in the thesis,and efficient sample pre-processing techniques were developed to significantly improve the detection sensitivity,as well as the reproducibility of Laser-induced breakdown spectroscopy(LIBS).Thereafter,chemometric algorithms were thus developed to accurately extract quantitative information of heavy metals from the complex and fluctuant LIBS spectra,and the rapid quantitative detection of heavy metal elements was implemented.The thesis is divided into two parts:In the first part,LIBS technique was applied to the quantitative detection of heavy metals in paste cosmetics.Taking the typical heavy metal elements including cadmium(Cd),chromium(Cr),and lead(Pb)as the research targets,a paste-solid conversion method based on dust-free filter paper was developed.Here,the LIBS spectra were collected after converting the paste sample into a filter paper coating.In order to effectively overcome the matrix interference,the characteristics of various spectral pre-processing methods were discussed thoroughly in the thesis,which were combined with variable selection techniques such as competitive adaptive re-weighted sampling,so as to accurately extract the intrinsic features of heavy metal elements from complex spectra.The results showed that the peak intensities of the heavy metal-specific emission lines were linearly proportional to concentrations,and the R~2of the linear regressions of Cd,Cr,Pb were up to 0.93.The limit of detection(LOD)of Cd,Cr,Pb were determined to be 1.3 mg/kg,2.0 mg/kg,and 2.4 mg/kg,respectively,which effectively met the national standard of allowable heavy metal contents in cosmetics(Cd:≤5 mg/kg,Cr:not specified,Pb:≤10 mg/kg).In the second part,the LIBS technique was applied to the quantitative detection of heavy metals in powdered cosmetics.Aiming at the detection of heavy metal elements such as Cd,Cr,and Pb,tablet processing was performed on the powdered cosmetics,which overcame the defects caused by the uneven surface of the powdered sample,then the LIBS spectra were collected.With the LIBS spectra,competitive adaptive re-weighted sampling model was developed to effectively overcome the influence of the powdery substrate on the signal,thus the intrinsic signal of heavy metal elements were accurately extracted.The results showed that the peak intensities of the heavy metal-specific emission lines were linearly proportional to concentrations,and the R~2 of the linear regressions of Cd,Cr,Pb were up to 0.96.The LOD of Cd,Cr,Pb were determined to be 4.2 mg/kg,5.9 mg/kg,7.6 mg/kg,respectively,which effectively met the national standard of allowable heavy metal contents in cosmetics.The results of the thesis show that,LIBS technique is feasible for the rapid detection of heavy metals in paste and powdered cosmetics,which meets the national LOD of heavy metals for cosmetics.The LIBS possesses a high-throughput analysis capability for the analysis of polymorphic heavy metals.Moreover,chemometric models are developed to suppress the interference of polymorphic sample matrix on the spectral signal,which improved the accuracy and prediction precision of quantitative analysis significantly.