Dear Manfred,

I apologise for not writing earlier. The truth is we are in a period of
protracted problems with our water delta 18-O mass spectrometer. There is
something wrong with the micro dual-inlet that is proving very elusive to
track down. The syetm has bee taken apart, cleaned and re-built but still
with problems. These show up as a drift in both the measured delkta 45 and
delta 46 values with time. The drift is severe and about 5 to 10 per mille
over a 24 hour period! The patterns of change are not what would be expected
from a simple leak, or poor valve closure.

Unfortunately also I have been away in New Zealand and so have not been able
to stand over my staff to ensure that they are working along the right
lines. Hopefully over the next few weeks I can sort things out and will be
able to report back to you with our measurements of VSMOW.

The problems we are encountering now may partially expalin the fractionally
heavier results we reported in the last round robin exercise. Once I
understand the cause of the effects I'll have a better idea if this is the

Best wishes,


Paul F. Dennis
Head of Stable Isotope Laboratory
School of Environmental Sciences
University of East Anglia

Tel: 01603 593105
Fax: 01603 507719
email: [log in to unmask]