Dear Mike,

It is my experience that all three manufacturers can deliver an instrument
whose measurement performance capabilities exceed those errors associated
with natural sample variability and the errors introduced during sample
preparation. There have been cycles over the years were each manufacturer
has been the one "in vogue". If you don't purchase a "lemon" and you don't
"abuse" the machine each will provide many years of service.

You suggest that small carbonate sample capability is one of your desires.
Small sample capability is a function of inlet volume and to some extent
sensitivity (which varies widely between individual machines, even of the
same type). Given reasonable sensitivity, a good clean source, a good clean
vacuum, and good filament placement it is the inlet volume that will
determine how small you can go. I would say that Micromass and thier
Microinlet come out on top in this category. I would also submit that
smaller volume analysers are easier to pump to lower vacuum (implying less
collisional detachment, lower background, etc, and therefore higher
relative sensitivity ie. you will collect more of what you ionize)
therefore Finnigan's 251 and 252 series and Prisms are less capable
instruments. I routinely run 20 ugm carbonate and have run as little as 6
ugms carbonate with less precision, on a not so sensitive Prism with a
microinlet. I am sure that if I had my carbonate prep device on my Sira,
which in my case is almost an order of magnitude more sensitive than my
Prism, I could be running unbeleivably small samples. My instrument of
choice for small carbonates would be an Optima, with microinlet and either
the new Gilson multiprep device or a common acid bath Autocarb.

Switching from oranges to apples, you also say you want an instrument to
run sulfer. It is my experience that the 'best" way to do this is by SF6 (I
am not saying you can't do it by SO2). SF6 obviates the large geometry high
dispersion instruments, your choice (in fact this is really all they are
good for, other than they look real flashy in a lab (G). Finnigan parts are
expensive and software is quirky. Micromass service and parts are a lot
better now after VG Fisons left. I beleive that Micromass may be phasing
out the Prism line, concentrating on the benchtop Isomass unit in the
future.

Switching from apples to now grapes you also say you want H/D and O-18 in
water and ice. Hoke bead equilibration for H/D and again the Gilson
multiprep are the way to go IMHO. My choice would be the Optima w/multiprep
a second time.

Switching from grapes to Kiwi fruit you also say you want continuous flow
capability. The boys from Europa were the originators of this type of mass
spectrometry, you should definately consider them if organic N and C are in
your future. I have a Carlo Erba hooked up to my Sira and have been very
happy with it's performance. I surmise that a Micromass Optima would fit
the bill as well.

If you tally it up I would say an Optima would be my choice for what you
want to do, other than sulfer as SF6 and then I would stick with a Prism.
If you are doing continuous flow sulfer I think the Optima is still the
best choice.  But, I do not recommend buying one machine and switching it
continously between a bunch of different prep devices, your overall
precision will suffer, besides it's a pain to switch it over once you have
one methodology dialed in. It is time consuming and expensive because you
have to tweek it each time and run standards, calibrations, etc. as
necessary for each new method. You do not just flip a switch and go from
sulfer continous flow one day to ultra small carbonates the next day!

Dedicated instruments may be the way to go so perhaps a bunch of Delta S's,
SIRA's or Isomass units would really be the hot setup, each with it's own
prep system tweeked to the max.

Best Regards,
Cap