Dear all,

there has been a lot of discussion about the (mainly leak-)problems with
GC/C/IRMS in the last time on this list, and I received a lot of useful
hints already.

Carl G. Johnson <[log in to unmask]> mentioned that he did nearly a
completely rebuild of the combustion interface according to the
reommendations given by K. Goodman (Anal. Chem. 70(5):833-837).

Now, I'm close to do a rebuild myself as well, but before starting, I
think I have to convince some people in our lab.

Hence my questions to this forum:

        1) First of all, is there anybody else who can report on
           experience with similar problems and a similar solution, i.e.
           more or less a single capillary interface? Not that I want
           Carl's contributions being depreciated in any respect; its just
           that additional reports would give more weight!

        2) When substituting the interface by a house made solution, how
           long does it take to have stable system running again?

           Are there any systematic deviations from the long term values
           of the laboratory standards?

        3) Are there any recommendations where to obtain the necessary
           parts from? I didn't find a vendor for the ceramic tubes yet.

        4) It seems to me that the tightness of the backflush valve is of
           significant importance for the peak shape and hence for the
           calculated d13C values. My experience is, that spraying Argon
           is not exceptionally useful here as the problematic fitting is
           located inside the valve. Furthermore in closed mode there is
           still some He purge. Therefore leaks are difficult to detect.
           The difference of m/z=40 between "Bfl on" and "Bfl off" (Thank
           you Carl!!!) is most helpful here.

           Now the questions: I don't get along using new fittings for the
           valve. What's the usual lifetime of the whole valve? To make it
           live longer would it be useful to put it outside the GC?
           I'm asking because it could be a workaround for the moment.


I know this is a lot of stuff, but I think there are a lot of people with
a lot of problems as well. Many, many thanks in advance, any hint is
appreciated!

Best ...

        Uli Flenker
        Institute of Biochemistry
        German Sports University Cologne
        Carl-Diem-Weg 6

        50933 Cologne / Germany

        Phone 0049/0221/4982-493