Frank (and Tom Brenna, who wanted references)
Yes, there can be fractionation of more than 20 (yes twenty) per mil for
delta 18-O by varying the flow regime from viscous-flow (capilliary at high
pressure differential) and molecular flow. There is a lot of old
literature from the time when men were men and mass spectrometers had just
been invented (and for the sake of PC, women were women too when mass
spectrometers had just been invented).
The theory of gas flow into a mass-spec was described by R. E. Honig (J.
Appl. Phys vol 16 p 646, 1945) and the practical data were published by R.
E. Halsted and A. O. Nier (Rev. Sci. Instrum. vol 21 p 1019, 1950).
The data (and the method) for extreme fractionation are in M. L. Coleman
and J. Gray (Rev. Sci. Instrum. vol 43 p 1501, 1972).
P.S. You may find the following interesting as an anecdote on the history
of mass-spectometry. The paper above by myself and John Gray was reviewed
by Al Nier. He wrote a very nice letter asking if we would correct a
long-established mistake in the popular name (and references to) the inlet
change-over valve, commonly called a McKinney valve. He told us that the
original idea (and publication) was by Byron Murphey from Nier's lab. (B.
F. Murphey, Phys. Rev. vol 72 p 834, 1947). Even 25 years later he said
that it still rankled that no credit hasd been given to Murphey for this
essential idea in the development of stable isotope mass-spectrometry. Of
course we changed our paper, but it didn't have much impact on what people
called the valve. So if you want to be correct you should refer to the
"Murphey valve" rather than the "McKinney valve."
>since I was not able to locate any information about it in the
>literature, allow me to post the question here:
>I am interested in the fractionation (13C/12C) that occurs
>when CO2 diffuses (or streams) through small openings or tubes. Is
>there any fractionation other than the mostly quoted +4.4 permille?
>If so, how is it related to the geometry (?) and size of the opening?
>Since this question must be of some importance for the design of mass
>spectrometers, I suspect quite some data will have been gathered
>Any hints or comments are VERY welcome !
>Stable Isotope Laboratory
>Department of Geography
>University of Wales, Swansea
>Swansea SA2 8PP
>Wales / GB
>Tel. +44 1792 295149
>Fax. +44 1792 205556
Max Coleman, Professor of Sedimentology
Postgraduate Research Institute for Sedimentology
The University of Reading
PO Box 227, Whiteknights
Reading RG6 6AB, UK
Phone +44 1734 316627
Fax +44 1734 310279
e-mail [log in to unmask]