ACI Avances en Ciencias e Ingenierías (Dec 2011)
Quantification of metal cations in water LIBS by deposition on a surface of steel striped with pencil HB
Abstract
The use of laser-induced breakdown spectroscopy (LIBS) together with a pencil lead substrate for the quantitative analysis of salts dissolved in liquids provides is introduced as a very efficient and sensitive analytical method. In this work we have compared five substrates over which aqueous solutions of salts were left to dry, and then submitted for analysis with LIBS. The comparison was based in analytical parameters such as the sensitivity and linearity of each substrate. We found that from these, the surfaces of graphite and a steel surface scratched with pencil HB gave the best results. The concentration of the salt (cation) in the solution was made to correspond to the areas ofspecific peaks for each corresponding atom. In this work, we used a method introduced by Jijón et al. [1] for data handling. This spectra selection method produces better linearity in calibration curves and much smaller errors that translate into correlation coefficients closer to 1, in this work correlations index up to 0.98 were determined. We introduced an experimental setup with mirrors to study the self-absorption effect, showing in this work the lost of linearity in the peak areas at high concentrations. We observed an indentation in the center of the Cs and K peaks, and the lost of signal LIBS of the spectrum of each peak analyzed with mirrors. In the last part of this work, we applied the methodology for quantification introduced to quantification of arsenic dissolved in water, as a real life application for concentrations until 1000 ppm. The non linear calibration curve for the whole range in this case was fitted to an exponential function with 0.993 of correlation index. The detection limit calculated for the arsenic in water was 3.2 ppm and this result is very satisfactory compared with those reported on literature for LIBS.
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