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Appl. Phys. Lett. 102, 244101 (2013).
Junshan Xiu, Xueshi Bai, Erwan Negre, Vincent Motto-Ros, Jin Yu.
Institut Lumière Matière, UMR5306 Université Lyon 1-CNRS, Université de Lyon, 69622 Villeurbanne Cedex, France and
Optics and Optoelectronics Laboratory, Ocean University of China, 266100 Qingdao, People’s Republic of China.
Abstract
Optical emissions from major and trace elements embodied in a transparent gel prepared from cooking oil were detected when the gel was spread in thin film on a metallic substrate and a plasma was induced on the substrate surface using nanosecond infrared pulsed laser. Such emissions are due to indirect breakdown of the coating layer. The generated plasma, a mixture of substances from the substrate, the layer, and the ambient gas, was characterized using emission spectroscopy. Temperature higher than 15 000 K determined in the plasma allows considering sensitive detection of trace elements in liquids, gels, biological samples, or thin films.
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Additional Information:
Direct determination of trace metallic elements in viscous liquids with laser-induced breakdown spectroscopy
Analysis of liquids and more particularly those with high viscosity may involve an infinite variety of materials, such as solutions, oils (edible or industrial), waste water, mud, creams, to name just a few. Elemental analysis in this type of samples can concern a large number of domains including the environment, petrochemical industry, agriculture, food safety, cosmetic and pharmaceutical industries. Facing to such vast field of applications, the current analytical science often offers inefficient solutions, especially when analysis is required in the context of in situ and/or rapid analysis. The most restrictive factor in analysis of viscous liquids by a conventional method such as ICP (OES or MS), corresponds to the time-consuming sample pretreatment, necessary because of the high viscosity of the samples. Laser-induced breakdown spectroscopy (LIBS) provides an effective method for elemental analysis without complex pretreatment. However, direct laser ablation of liquid is a very inefficient process because of the specific coupling mechanisms of the energy deposited by the laser pulse in liquid, which may lead to the generation of bubbles or surface waves. We have recently introduced an innovative procedure in LIBS technique applied to the analysis of viscous liquids. This procedure consists in applying the liquid to be analyzed in thin layer (~ 10 µm thick) on the surface of a pure metal target, aluminum for example, and in inducing a metallic plasma through the liquid layer. The metallic plasma can reach a temperature of several tens of thousands Kelvin and propagates under the constraint of the liquid layer. The interaction between the metallic plasma and the liquid finally results in a mixture of gaseous materials, at high temperature and highly ionized, originated from the metal as well as the liquid. The high temperature of the mixture plasma leads to its strong emission for an efficient LIBS detection [1]. Limit of detection in the range around the ppm has been demonstrated for many metals such as Ag, Cr, Cu, Fe, Mg, Na, Ni, Pb, Si, Sn, Zn and Ti [2]. We observed also a negligible matrix effect when different oils (lubricating oils and cooking oils) are analyzed with the use of a same metallic substrate, due to the fact that the property of the induced mixture plasma is mainly determined by the plasma induced from the metallic substrate [3]. Finally this method has been tested with success for liquids with very high viscosity such sun creams. In the last case, since metallic elements (Ti and Zn) are included in a base cream with quite high concentrations in the range from 1 to 10 %, we have established an efficient procedure for properly selecting emission lines for concentration determination with reduced self-absorption effect [4].
[1] J.S. Xiu, X.S. Bai, E. Negre, V. Motto-Ros, J. Yu, Appl. Phys. Lett. 102 (2013), 244101. [2] J.S. Xiu, V. Motto-Ros, G. Panczer, R.E. Zheng and J. Yu, Spectrochim. Acta B, 91 (2014), 24 – 30. [3] L.J. Zheng, F. Cao, J.S. Xiu, X.S. Bai, V. Motto-Ros, N. Gilon, H.P. Zeng and J. Yu, submit to Spectrochimica Acta B, (2013). [4] J. Menneveux, F. Wang, X.S. Bai, Y.P. Chen, V. Motto-Ros, N. Gilon and J. Yu, submitted to the 8th International Conference on Laser-Induced Breakdown Spectroscopy, (2014).
