HI John--

We've run polyethylene foil (PEF-1, <100ug) then biotite (NBS-30, ~2mg) 
for D/H, and saw ca. -103 and -69 respectively (sorry, no statistics on 
hand right now, but std dev < 3 per mil if I recall correctly). In both 
cases, we got clean peaks 3 to 6 V on mass 2 (1 to 2 V on mass 3)--run a 
DeltaPlus XP. Newly packed reactor w/ crucible run at ~1450, with 8 min 
run times to let the CO peak level out (sample drop ~70 sec, switch to 
CO at ~170 just to follow it, not for isotopes).

take care

gerry



John Dilles wrote:
> Hi all
>
> We have been restandardizing for D/H mineral analyses on our TCEA unit 
> (running at 1450°C) connected to a CF mass spec in Alan Mix's lab. In 
> parallel the U of Oregon lab has been doing the same. We have run into 
> a problem in that biotite standards are yielding different D/H ratios 
> compared to one muscovite standard. We are using NBS-30 biotite 
> (nominal values something between -65 and -67 ”) and as a primary 
> standard, and Misasa sericite/muscovite (Kusakabe, person commun. 
> 2007; -59.1 ± 0.3 (2 std error of mean) as a secondary standard.
>
> Both the OSU and U of O labs have gotten results for H2 gases derived 
> from Misasa sericite that are isotopically lighter than the gases 
> derived from NBS-30 biotite.
>
> For example, in a 2005 run, using NBS -30 as a nominal standard, we got:
>
> NBS-30 Biot Misasa Sericite
> accepted value (~-66”) (-59”)
> measured -67.3±2.9 -73.6±1.4
> analyses n=4 n=5
>
> I am puzzled because the Misasa sericite is a well-behaved standard 
> according to Dr. Kusakabe, and in our experience running it for 
> several years as a secondary standard in our conventional D/H lab 
> (using a 1400°C resistance furnace, and U reduction of water to H2).
>
> So far, our working hypothesis is that in the TCEA, the H2 gas 
> liberated from biotite at 1450°C has a significantly different offset 
> (fractionation?) from original biotite, compared to H2 gas liberated 
> from muscovite. Maybe this has something to do with Fe-bearing minerals?
>
> Anyone else seen this, or have any suggestions for an explanation?
>
> Cheers,
>
> JOHN Dilles
>