Dear Jim O'Neill,
as the person responsible for the development of the isotope mass spectrometers
at the Finnigan factory in Bremen, I need to inquire about your statement that
one cannot "get anywhere near the correct dD value when it is large" with a
modern machine (Delta-S).
Being aware of the performance of a larger number of machines and with some
experience in measuring the SMOW/SLAP values both from equilibration and from
reduction experiments I simply cannot share your judgement. The contrary is the
case: we get very close to the -428 permil without scaling, using the
"questionable H3+ factors" determined in an automated fashion and applying the
correction for H3+ contribution as available in the software. If we are missing
"some important factor" we would very much like to be informed as early as
possible in order to keep a possible damage to data in the literature as small
as possible.
Willi Brand