Stable Isotope Geochemistry


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Andrew Tait <[log in to unmask]>
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Stable Isotope Geochemistry <[log in to unmask]>
Thu, 29 Jan 1998 21:51:30 +0000
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Richard Crombie wrote the following about 66 SO2 WOES (fwd):

> Hello, folks,
> I run a Carlo Erba NA1500-Optima with both DI and continuous flow.
> It was set up to run C and N isotopes only, and I am
> attempting to obtain 34S from 66SO2. I have made all the
> physical upgrades for this, and am running conflow, using the
> DI ref system as my source of SO2 ref gas.
> I have run samples against my ref gas(set at 0.00 per mille
> for now) and have good traces, but the computer does not
> calculate them. The print out for isotopic calculations reads
> "no peak", and "0.00" for its calculation of delta and atom%
> values. Also Std Dev of fit is "N/A".
> I THINK it is a software problem. The software is EA 1.4.
> Any words of advice from seasoned users?

The two obvious things which spring to my mind are to do with baseline
calculation.  Is your C/O valve closed when the software is doing its
zero measurements at the beginning and/or end of the run?  If not, you
will have a large positive zero, which will make the apparent beam
heights very small. The other possibility is that your peak thresholds
are set too high.  For SO2 you will have smaller major beams than for
CO2 and N2. Go into DP, and load a trace.  Display the zeros, and see
what level they're at, and whether they represent a "zero".  For the
time being, lower the sample peak threshold to 1e-10 or even 5e-11.
You can always ignore spuriously integrated peaks.

Let me know how you get on....

Totty  <8^)