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Wed, 6 Apr 2005 14:07:25 -0600 |
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I don't have much to add since many that have replied do much as I
do. However, I'll put in my 2 cents worth on a 2-3 small items.
1. As often as practical, I run oxygen first. I then put samples
together of similar isotopic composition on the HDevice so that the
memory influence from one sample to the next is minimal.
2. I've also found that picking up and discarding 4-5 aliquots of
the next sample, followed by repeated purging of the needle,
decreases memory in my system to <0.5%.
3. I also use calibrated secondary standards for normalization
purposes, the heavier of which is reasonably close in composition to
most unknowns. This is also the standard I use to monitor and
correct for fractionation in the bellows. Thus, in a single batch it
gets run a lot, and when I do the normalization, I have a good
central tendency for it. This properly exerts more influence on the
normalization regression.
--
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Steve Nelson
Dept. of Geology
S389 ESC
Brigham Young University
Provo. Utah 84602
voice: 1-801-422-8688
lab: 1-801-422-5124
FAX: 1-801-422-0267
CARPE CARP: seize the fish
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