Dear Brian,
The minimum number of organisms needed for SI analysis is a nightmare for 
many people...

I have found some useful informations in this paper:
Small sample methods for d13C and d15N analysis of the diets of marsh 
meiofauna species using natural-abundance and tracer-addition isotope 
techniques- Carman and Fry- MEPS- 2002-240:85-92

Because I did not have access to the setup described in the paper, we were 
able to run samples of 100ug, using the 600uA trap current and particular 
care preparing the samples (marine and freshwater zooplankton, i e about 12%
N and 50%C). We wrote a technical note on this (Tell me if you want a pdf).

All the best
Jerome.

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