I'm sure Willi (Brand) can shed some light on your observations with glassy
carbon at temperatures below 1300 C for 18O analysis. Personally, I figure
it might be a case of the Boudoir equilibrium for CO2 <-> CO being shifted
towards higher temperatures for 90%+ CO yield in systems where (a) the
product is continuously removed and (b) reactants are moving pretty fast
given the high He flow rate in the furnace.
I am running our TC/EA at 1400 C for 2H and 18O analysis and have
experienced no problems (we are using IAEA-OH1 to OH4 as standards). Ditto
when running organic materials.
Only exception thus far are nitrates; here I found the optimum temperature
for 18O (in terms of consistent results for the IAEA-NO3 standards) to be
1350 C. That's the "lowest" temperature I have run our TC/EA since higher
temperatures seems to be counterproductive for 18O of nitrates.
> -----Original Message-----
> From: Stable Isotope Geochemistry
> [mailto:[log in to unmask]] On Behalf Of tlarson
> Sent: 31 May 2005 21:17
> To: [log in to unmask]
> Subject: Related Hi temp EA question
> I'm shopping for a new EA to lighten the work load of my
> current one (Euro
> EA) that we use for typical EA stuff: basically CN isotopes
> and ratios in organics. We also run a lot of waters using
> chrome reduction at 1075°C. I'm considering a high temp that
> will be used solely for glassy carbon reduction in solid
> samples and chrome HD for water.
> I've run oxygen using glassy carbon at lower temps (1100°C),
> but wasn't thrilled with the results. Interestingly, at
> 1250°C the results were worse. Is life really that much
> better at 1400°C for glassy carbon? Aside from the Finnigan
> TCEA, what other high temp EA brands have folks had good success with?
> Toti Larson Ph.D.
> Los Alamos National Laboratory
> Earth and Environmental Sciences 505.667.9894 (lab)
> Los Alamos, New Mexico 87545 550.667.8006 (office)