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Mass Spectrometry & Spectroscopy


Fluorine Analysis Using Molecular Absorption Spectroscopy


Dr. Tobias Frömel, Head of the Department of Organic Mass Spectrometry, Institute for Analytical Research, Fresenius polytechnic Sascha Münster-Müller, Masters student, Fresenius polytechnic, Idstein Professor Dr. Thomas P. Knepper, Director of the Institute for Analytical Research, Fresenius Polytechnic, Idstein


Fluorinated organic substances gained in importance in recent decades, because substitution with fl uorine holds many benefi cial characteristics for the application. Not only fl uorinated polymers, such as polytetrafl uorethylene (PTFE, Tefl on®


)


are encountered at many places in everyday life, but many low-molecular organic substances also contain one or several fl uorine atoms, for example, some pharmacologically active substances, such as fl uoxetine (see Figure 1), as well as pesticides, such as tolylfl uanide (Figure 1). In the past decade perfl uoroalkyl and polyfl uoroalkyl (PFASs, formerly also PFC = perfl uorinated and polyfl uorinated compounds or PFT=’perfl uorinated tensides’) gained great attention. This class of substances of which perfl uorooctanoic acid (PFOA) and perfl uorooctane sulphonic acid (PFOS) are the most researched substances, have many negative properties for people and the environment [1].


Molecular Absorption Spectroscopy of Gallium Fluoride


Figure 1. Structural formulas of various fl uorinated organic compounds


Since the common methods of today for the quantifi cation of known substances utilise methods with a defi ned analyte spectrum, mainly the high performance liquid chromatography coupled with the tandem mass spectrometry (HPLC-MS/MS), unknown compounds of this substance class are not detected by the method. However, some studies lead to the result that the content of unknown PFASs in environmental samples exceeds that of specifi c individual substances [2].


For this reason a cumulative parameter for organic fl uorinated substances, similar to the AOX value, would be desirable. This could play a role as routine method, e.g. in galvanic wastewater, drinking water, after enrichment of the analytes and separation of matrix substances, but also in food analysis. However, common digestion methods fail for PFASs due to the very strong C-F bonding which withstands both high thermal and chemical loads [1; 3; 4].


Here, the molecular absorption spectroscopy (MAS) forms an elegant option for detecting organically bound fl uorine. In several examinations fl uorine was analysed using this method [5; 6]. This is implemented by the MAS of GaF, which is formed by adding Ga(III)-nitrate under moderate temperatures. The resulting GaF can be measured with an atomic absorption spectrometer with continuous light source and high resolution optics at a wavelength of 211.2480 mm (Figure 2). The sample is put through a temperature/time program in a graphite tube furnace causing the formation of GaF which is then detected by spectroscopy. To this end a contrAA®


700 was used with autosampler AS-GF (Analytik Jena, Jena).


Figure 2. contrAA®


700 by Analytik Jena


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