I just wanted to respond with my sincere thanks and gratitude for everyone who chimed in to provide their respective experience and working techniques. This has been an invaluable read. 

Happy fractionating! 
Chris

________________________________________________
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





> On Oct 26, 2017, at 9:58 AM, Fabien Dewilde <[log in to unmask]> wrote:
> 
> Dear all,
> 
> 
> With a dual inlet IRMS Isoprime (Elementar) at LSCE (Gif-sur Yvette, France), we can run small carbonates down to 10 µg, even a bit less, with a precision better than 0.08 (1 sigma) for d18O and 0.04 (1 sigma) for d13C. For masses above 20 µg, it is the traditional precision, ie: < 0.05 for 18O and < 0.03 for d13C.
> About the recipies, everything have been told in the previous comments such as:
> 
> . giving up linearity for sensitivity (by playing a bit with the extraction voltage by example)
> 
> . balancing the capillaries for the kind of signal you have with low masses
> 
> . lowering the refill of the "reference" gas to about 20% less than the signal you have with low masses
> 
> . increasing a bit the trapping time to the coldfinger
> 
> 
> The most important is that you should run a batch of only small carbonates (between 10 and 20 µg) with a little bit more carbonate standard than for bigger masses. I observed no differences for d18O for small carbonates (except a less good precision) but for d13C, values are getting lighter as masses are getting smaller.
> 
> It is the same behavior than Alan showed in his answer (but only for d13C for me and the decrease starts around 20 µg).
> 
> As Alan said, I don't want to apply slope corrections as a function of signal. So, it is better I think, when you have small carbonates, to not mix them with other bigger samples.
> 
> 
> Fabien Dewilde
> 
> 
> 
> 
> Le 25/10/2017 à 16:30, Christopher Maupin a écrit :
>> 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 <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] <mailto:[log in to unmask]>, [log in to unmask] <mailto:[log in to unmask]>
>> Mobile: (512) 810-8437
>> 
>> 
>> 
>> 
>> 
>