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M. Weiss, Z. Gajarska, J. Lohninger, G. Ramer, B. Lendl, A. Limbeck:
"LIBS analysis of Fluorine in solid samples via measurement of molecular emission bands";
Poster: AOFKA - Applied Surface and Solid State Analytics, Freiberg; 06.10.2021 - 08.10.2021; in: "Scientific program - Abstracts", (2021), S. 52.

In recent years, fluorine analysis has become increasingly important due to its applications in high performance polymers, membranes, surfactants and pharmaceuticals, as well as due to the potential environmental harm of its compounds. Despite its importance, its accessibility by analytical techniques remained limited. One of the techniques showing a potential for the fluorine detection is LIBS (laser induced breakdown spectroscopy), however, the high excitation energy of this element limits the sensitivity of the analysis and its possible applications. Nevertheless, this limitation can be circumvented by a well-established method of detecting the molecular emission of the element of interest instead of detecting the atomic line itself. In LIBS, such molecules are formed by recombination of atoms upon the plasma cooling. For analytical purposes, either an element naturally occurring in the sample or an element intentionally added to the sample can be used as a partner for the molecular formation. In the literature, several approaches of the latter are reported, including spiking of a powdered sample with an additive or introduction of a nebulized liquid standard on the sample surface during the LIBS analysis.
As these approaches allow only for the bulk analysis of the sample, we would like to present a novel method for the introduction of the element acting as a molecule building partner for the fluorine detection, opening up the possibility of its imaging. The proposed methodology is based on sputter coating, allowing to apply homogenous films with a thickness in the nano- to micrometer range on the solid surface. Our work includes the investigation of several candidate elements as well as the optimization of the film thickness and LIBS measurement parameters.
Finally, we demonstrate the applicability of the developed procedure for actual research tasks, in particular the quantitative measurement of fluorine in polymer samples, and the mapping of the fluorine distribution in polymers.

LIBS, Fluorine, polymer analysis, imaging