We have analyzed ~300mg samples in our Costech before. Our EA has a modified 25mm reactor in the top half, which allows for a little more ash buildup before samples get out of the hot spot.
With a stock 18mm reactor you likely will get out of the hot zone after just a few samples. I suggest running without an ash insert to get the maximum ash volume possible for your samples. An ash vacuum will allow for longer maintenance intervals.
As to your oxygen loop, semi micro may very well be enough O2. It is the C in the sample, not the physical size that seems to be the primary driver of oxygen need. We typically select the O2 loop based on the weight of C in the sample. Some soils could probably combust fine on a micro loop even.
It would be a good idea to make sure your EA timing is optimized, sample delay, run time, etc. to get thorough combustion. Also try to target standards, gas pulses all in the low signal range, ideally across a range to create a linearity curve.
Manager, Stable Isotope Core Laboratory
Washington State University
367 Eastlick | Pullman, WA 99164-4236
Office: 509-335-6161 | Lab: 509-335-6154 | Fax:509-335-3184
Anybody ever run a 300mg sed sample w/ very low (<0.5%) carbon and nitrogen by EA-IRMS ?
I am wondering if a Costech 4010 ECS semi-micro loop for oxygen will be adequate for
Thanks - Sarah