MAT252, Kiel-III, capillaries balanced at low voltage, cleanliness is next to godliness, no slope corrections, “normal” glass reaction vials.  

Results to 10 micrograms on calcite standards — see graphic below (in the 10-21 microgram range, d13C external precision of 0.03 to 0.04, d18O external precision of 0.03 to 0.06 --two different numbers because two different standards, offset between standards maintained at about 5.5 permil for d18O, 1.2 permil for d13C, so no problem with gas mixing or memory).  Results on real biological samples will be less precise because of, well, biology.  

I’m not particularly fond of approaches that that do slope corrections as a function of mV as they can make standards look OK but you never really know they are right. Not religious about this, but very cautious. Can’t fight physics  — if the capillaries jump flow regime at low pressures, that’s the limit and the two sides don’t necessarily do it at exactly the same point.  On our current system, the practical limit appears to be about 10 micrograms.

Alan.

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Alan C. Mix, PhD
Distinguished Professor of Earth, Ocean, & Atmospheric Sciences
President of The Oceanography Society (www.tos.org)
Fellow of the American Association for the Advancement of Science
Fellow of the American Geophysical Union

Oregon State University
CEOAS Administration Building 104
Oregon State University
Corvallis, OR 97331-5503 USA

email: [log in to unmask]
www: http://ceoas.oregonstate.edu/profile/mix/

On Oct 25, 2017, at 7:30 AM, Christopher Maupin <[log in to unmask]> wrote:

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