Yes. Ditto that on the ref gas pressure.  The low end usually falls apart from bad pressure adjust on the ref side as it is trying to hit a moving target on the sample side, and of course this becomes critical as the sample is disappearing during the wait time.  There is a bit of hysteresis on the bellows, so keeping it somewhere in the middle is good. At one point we monkeyed around with the pressure adjust parameters to adjust fast while minimizing pressure hysteresis effects - can’t remember exactly. Each bellows I’ve had seems to have a bit of its own personality, so it is hard to say specifically what will work. A.

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> On Oct 25, 2017, at 2:59 PM, Ambrose, Stanley H <[log in to unmask]> wrote:
> 
> Hi Chris,
> 
> One strategy to add to the good advice from the rest of the community:
> 
> In dual gas mode on the 252 with the Kiel, lower the reference gas pressure (refill time can be reduced in the methods) so the voltage at 50% bellows expansion matches the voltage generated by the average 15-20 µg calcite sample.  The mass spec will spend less time balancing sample and ref major ion beam and get on with analysis before the sample bleeds away.
> 
> Test working standards at a variety of weights and refill times to get the right voltage range.
> 
> Stanley H. Ambrose, Professor
> Environmental Isotope Paleobiogeochemistry Laboratory
> Department of Anthropology
> University of Illinois
> 109 Davenport Hall
> 607 South Mathews Avenue
> Urbana, IL, 61801, USA
> Phone 217 244-3504
> http://www.anthro.illinois.edu/people/ambrose
> 
> From: "[log in to unmask]" <[log in to unmask]> on behalf of Christopher Maupin <[log in to unmask]>
> Reply-To: "[log in to unmask]" <[log in to unmask]>
> Date: Wednesday, October 25, 2017 at 9:30 AM
> To: "[log in to unmask]" <[log in to unmask]>
> Subject: [ISOGEOCHEM] Carbonates under 20 micrograms? Under 10 micrograms?
> 
> Dear Isogeofolks, a broad, community query here: 
> 
> I’m curious what your successes and/or failures running extremely small carbonate samples have been like. Seeing the uptick in individual foram papers in recent years as piqued my curiosity to reach out to the broader iso-sphere. 
> 
> What instrument/peripherals have you tried/are you using?
> What are the smallest masses of CaCO3 you are able to successfully measure?
> What precision are you routinely achieving on these successful measurements? 
> What is your “recipe” for success?
> 
> Many thanks!
> ________________________________________________
> Chris Maupin, Ph.D.
> http://christophermaupin.strikingly.com
> Research Associate and Facilities Manager
> Stable Isotope Geosciences Facility (SIGF)
> Geography Department
> Texas A&M University
> 405 Eller O&M Building 3147 TAMU
> College Station, TX 77843 USA
> Email: [log in to unmask], [log in to unmask]
> Mobile: (512) 810-8437
> 
> 
> 
> 
>