>Dear Listmembers,
>
>I am planning on an oxygen extraction line for small water samples
>(1-10mg). The liberated oxygen shall be analysed on an isotope ratio
>mass spectrometer for 18-O, 17-O and 16-O. So far, I’ve only found the
>papers by O’Neil & Epstein (1966) and Clayton & Mayeda (1983) related
>to milligram quantities of water and 17-O, respectively. Now, I wonder
>if the isogeochem pool can help me with the following questions:
>
>1.) Many laser ablation lines use fluorine gas instead of BrF5 for
>oxygen extraction on minerals. How suitable is fluorine gas for water
>samples? What is the minimum temperature required in order to avoid
>the production of any oxy-halogen compounds?
>
>2.) After the recent lively discussion on Kel-F, I wonder if I can use
>it for reaction vessels. I wouldn’t like to use Ni or stainless steel
>since metal fluoride is quite hygroscopic. Does Kel-F stand
>temperatures of up to 200°C for 10-20 minutes?
>
>3.) Who supplies Kel-F in Europe?
>
>4.) In case of fluorine gas: Does anybody know if N2 and F2 combine to
>NF3 at 100-200°C? In other words, do I need to purify the fluorine gas
>first?
>
>5.) Who can recommend me a source for molecular sieves suitable oxygen
>gas purification?
>
>Any comments, further references, ideas, etc. are very much
>appreciated!
>
>
>Thorsten
>
>
>Thorsten Agemar
>Institut fuer Umweltphysik
>Universitaet Heidelberg
>INF 366
>D-69120 Heidelberg
>Germany
>
>+49 (0) 6221 54 6334
>+49 (0) 6221 54 6405 (FAX)
>[log in to unmask]

Thorsten:       We still do water fluorination on few-milligram samples
(for another reference, see Matsuhisa et al. GCA 42,173,1978). We use BrF5
(why would you want to use fluorine?) in a nickel reaction vessel. Heating
to about 200degrees C is necessary to decompose metastable products, such
as ozone and peroxides formed in the explosive reaction.
        If NF3 were produced, it can be recognized in the mass spectrometer
by its fragment at mass 52 (NF2+). We purify oxygen before mass analysis
using 13X molecular sieve (30/60 mesh, Anasorb), to remove any NF3 or CF4.
                                                Bob Clayton