Fluorine combustion analysis

A new analytical technique, fluorine combustion analysis, is based on the fact that fluorides of elements in high oxidation states are thermodynamically stable, often volatile, and very strong infrared absorbers (Jacob, 1989). This method is especially suited to the... 

The assumption is made at present that elemental combustion analysis for carbon, hydrogen, and fluorine provides a good approximation to the extent of incorporation of fluoroalkyl residues, i.e. alcohols and ethers. We have ruled out trifluoromethylcarbonyl groups since no evidence is seen for their presence in either the infrared spectra or the 19F-NMR spectra. Thus, our values for percent modification reflect the best fit of the combustion data to an idealized stoichiometry for the product in Equation 1, where (m+n+o) = 100, and the percent modification (% mod.) is given by the expression [100 x (m+o)/(m+n+o)], equivalent to the number of fluoroalkyl residues per one hundred methylenes. An appropriately normalized formula was used to fit the data for polypropylene (sample 10). 

Table 8.47 shows the available options for the analysis of polymer processing aids, namely combustion and instrumental methods. The best method is dependent on PPA type, the level to be measured, and the available equipment (see also Section 8.2.1.2). Fluoropolymer processing aid concentrations can be determined by WDXRF configured to measure either fluorine or a tracer, and by EDXRF to analyse a tracer [29]. Calibration curves are required. At present, EDXRF or benchtop XRF units cannot directly measure fluorine. For resin or masterbatch producers who prefer to make on-line XRF measurements of processing aid concentrations (to letdown levels of 50-100 ppm), processing aids that contain a tracer (usually BaS04) are available. The analysis time is less than two minutes. 

The major differences between the fluorine and oxygen combustion calorimetry methods arise from the exceptional reactivity and toxicity of fluorine. The substances studied by oxygen combustion calorimetry are normally stable when kept inside a bomb at 298.15 K and under 3 MPa of O2. Oxygen- and moisture-sensitive compounds can also be studied because various types of containers are available to prevent their reaction with O2 prior to ignition. Common examples are glass ampules, which are inert toward the combustion process and, more commonly, Melinex bags or polyethene ampules, which burn cleanly to CO2 and H2O. As carbon dioxide and water are also generated in the combustion of the sample, no extra complexity is introduced in the analysis of the final state of the bomb process by the use of those plastic containers. 

The gaseous product (SF6) does not interfere with the analysis of solids that form in the main bomb process. Furthermore, the contribution of reaction 7.82 to A f/jgp can be accurately calculated lfom the mass of sulfur and the value of ArC/°(7.82) at 298.15 K [124], It may also be necessary, in some cases, to use an auxiliary substance to promote complete combustion of the compound under study [111,113]. Tungsten is a very common combustion aid it reacts cleanly with excess fluorine according to... 

Continuous analysis of highly fluorinated materials can present problems, primarily caused by the corrosiveness of hydrogen fluoride which is liberated from all of them during combustion. Hydrogen fluoride will react with the permanently bound hydroxy groups on the surface of the cooler parts of combustion tube walls and catalysts. The effect can lead to erratic hydrogen values and so the installation of some type of oxide [magnesium oxide, alumina, or cerium (IV) oxide] trap in the combustion tube to prevent its escape is recommended. 11... 

Miyake, Y, Yamashita, N., So, M. K., Rostkowski, P, Taniyasu, S., Lam, P. K. S., et al. Trace analysis of total fluorine in human blood using combustion ion chromatography for fluorine a mass balance approach for the determination of known and unknown organofluorine compounds. J. Chromatogr. A, 1154 214-221 (2007). 

The homogeneity has been verified at the level of intake of 0.25 g. The method uncertainty was measured by seven replicate analysis of dissolutions of a coal CRM (NBS 1632a). F and Cl were determined by ion chromatography after oxygen combustion and absorption in water cooled in ice. No in-homogeneity was detected for fluorine. For Cl, a significant difference between the CV of the method and the CV between-bottles was demonstrated the very low Cl content led to a large uncertainty of measurements which could, however, not explain the differences observed in the within- and... 

In the case of fluorine, doubts were thrown on the reliability of the oxygen bomb combustion. This method might give correct results for the analysis of some coal matrices but fusion should be systematically used in the case of fly ash consequently. 

KEYWORDS fluorine, fluorine, fluoride, ion-selective electrode, fuel analysis, oxidative combustion, elemental analysis... 

All of the previously described methods have a separate combustion step prior to detection. A combination of combustion and detection in one instrument would greatly enhance the determination of fluorine, making it simple and rapid to operate and suitable for automation. The goal was to develop a rapid, sensitive, and accurate method with safe operation for the analysis of fluorine in liquids, solids, and gases with little to no sample preparation. 

The oxidative combustion wifli ion-selective electrode method described here can be used to accurately determine fluorine in liquid hydrocarbons and liquefied petroleum gases at levels down to 0.5 ng/pl. Results obtained are in good agreement with those achieved with the Wickbold Oxy-Hydrogen Combustion method. The oxidative combustion with ion-selective electrode method is less time consuming, less hazardous, and more sensitive than the Wickbold method. The analysis is also applicable to a range of sample types not discussed here, including aqueous based systems and solids. 

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