Avaliação da espectrometria de emissão óptica com plasma induzido por laser (LIBS) para a determinação de Ba, Cd, Cr e Pb em brinquedos

Abstract

LIBS is a spectroanalytical technique that employs the microsampling by laser ablation and subsequent exitations for atoms, ions and molecular fragments presents in induced microplasm.This technique was evaluated for determination of Ba, Cd, Cr and Pb in samples of toys and for the application of classification methods. A Q-Switched Nd: YAG laser (Brilliant, Quantel, France) operating in the fundamental wavelength (1064 nm) with repetition rate of 10 Hz and spectrometer model ESA3000 (LLA Instruments Berlin, Germany) with optical Echelle and ICCD detector was employed. Samples were cut in circles of 3,0 and/or 1,5 cm diameter, fixed in sample holder and coupled in a sampler. Laser pulses were focused in the surface of sample. Ten accumulated LIBS spectra were collected in different positions of each sample and the average of these spectra was used to represent a test portion. Software ESAWIN, NIST database and an algorithm developed in MATLAB® were used for acquisition and data processing. Variables optimization was realized using 24 factorial design and Doehlert. Operational optimized conditions consisted of: 18.0 cm lens-to-sample distance, 50 accumulated laser pulses, 6.0 μs integration time gate, 2.0 μs delay time and 250 mJ laser energy per pulse. Two strategies were proposed for calibration, in the first one used toys samples for building calibration curves and the second one used pure polymers of HDPE and PP for calibration. The curves obtained presented good correlation and was observed that laser-polymer interaction depends of chemical composition of polymer. The comparison of results obtained with LIBS and ICP OES not were very consistent, probably due to the mixture of polymer matrices and for samples HDPE+PP, it was not possible to build curves with a mixture of these matrices. However, is possible to use LIBS for evaluate semi-quantitative presence of analytes in toys. xxi Leaching tests were realized in all sample toys. Values obtained were compared with values established in the technical Norms NM 300-3:2002 and EM 71- 3:2002. The results showed that few toys samples exceeded the values established by norms after of leaching test, despite Cd, Cr and Pb have been found in some samples with total values above established values. The classification of toys samples were realized using the classification models SIMCA, KNN and PLS-DA, allowing adequate classification of toys contaminated with Cd, Cr and Pb.