Fluorine, detection

Atmospheric flash drying, in bar soap manufacture, 22 750-751 Atmospheric fluorine, detection of,... 

Megaelectron volt (MeV) ion beam techniques offer a number of non-destructive analysis methods that allow to measure depth profiles of elemental concentrations in material surfaces. Elements are identified by elastic scattering, by specific nuclear reaction products or by emission of characteristic X-rays. With nuclear microprobes raster images of the material composition at the surface can be obtained. Particle-induced gamma-ray emission (PIGE) is especially suited for fluorine detection down to the ppm concentration level. 

The technical aspects of fluorine detection by nuclear reactions as well as its applications to fluorine analysis in geological and archaeological objects are reviewed. Special attention is given to the determination of exposure ages of meteorites on the Antarctic ice shield and burial durations of archaeological bones and teeth. This information can be acquired by evaluation of the shape and penetration depth of the diffusion profile of fluorine that was incorporated by the sample from the environment. For a quantitative assessment of the data, several factors like ambient conditions and diagenetic state of the material have to be taken into account. 

In the following, those ion beam analysis techniques that allow for fluorine detection will be presented. By far, the most important technique in this respect is nuclear reaction analysis (NRA). Although it can be rather complex to perform, it is the most often applied technique for fluorine trace element studies, due to a number of convenient and prolific resonant nuclear reactions which make it very sensitive to fluorine in most host matrices. NRA is often combined with particle-induced X-ray emission (PIXE) which allows for simultaneous determination of the sample bulk composition and concentrations of heavier trace elements. By focusing and deflecting the ion beam in a microprobe, the mentioned techniques can be used for two- or even three-dimensional multi-elemental imaging. 

If proper care is taken a fluorine detection limit of roughly 1 ppm in thick targets can be obtained with both the 19F(p,ay)160 and the 19F(p,p y)19F reaction. As a general rule of thumb it can be said that 0.1% of fluorine can usually be detected without difficulties, while 1 ppm can only be reached under optimized conditions. Additional information on sensitivity can be found in literature (e.g. [1,2,41,60]). Although published data can be of help in evaluating the appropriate analytical technique, it should not be the substitute for a practical experimental test in the case of an unknown matrix. 

PIXE is the analogue to EDX/WDX (energy/wave dispersive analysis of X-rays) done with electron microprobes. Elements in the sample are identified by the characteristic X-rays emitted during MeV particle bombardment. PIXE is not well suited for fluorine detection because of the low energy of the corresponding X-rays. However, it is often performed simultaneously with other ion beam techniques and gives very valuable information on the bulk composition and other trace element concentrations in the sample. 

When a commercially available mixture of perfluoroheptane isomers was used instead of perfluoroethane, the amount of fluorine detected by XPS analysis was much higher. The F C ratio was 0.9 1 to 1 1 for wool and 1.4 1 to 1.5 1 for synthetic polymer substrates before extraction. Fig. 5 and 6 show the deconvoluted carbon Is spectra for both examples. Extraction reduced the fluorine content uniformly by 25-40 The F C values after extraction are higher than for hexafluoroethane. F agmentation of perfluoroheptane isomers can create a wide variety of perfluoroalkyl radicals which may couple with the surface. 

Three channel C- F HSQC and HMBC experiments with fluorine detection have been used by Ampt et to measure /cf. fHC. Vhf and /ff couplings for three fluorinated compounds, the fluorinated steroid, 1,1,2,2-tetrafluoro-2-iodopropane and 1,2-dichloro-3,3-difluoro-1 -propene. The signs of couplings have been deduced from the splitting displacements. 

A suite of coupled/decoupled versions of fluorine-detected triple resonance H HSQMBC and HMBC spectra of fluorinated compounds... 

The fluorine sensor is extensively used conunerdally. The fluorine content can also be detected by chemical sensing and the principle of this device also belongs to type II. The base material is lanthanum fluoride, which is an excellent fluorine conductor, and which is stable even in aqueous solution. A typical plication is to measure the fluorine content in test water solutions. The principle of fluorine detection is based on the F concentration cell method. The detection limit is as low as 10 M, which covers most F" concentrations in drinking water. A fast response is one of the typical characteristics of the type-II sensor it is less than 3 minutes even if the F content is as low as 10" M. 

Several F-F and F-C 2D correlation experiments, which were already known or which were modified for the use with fluorine detection by the authors have been presented by Aspers et al. It included /-HMBC, XLOC, HMQC and COSY-10 experiments... 

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