Hi Anthony--

1.  Old water baths that have been continously refilled, without drying
out completely, can serve as a source of relatively heavy  water--or get
some bottled  water from Texas (close to VSMOW, which I found as
"American Fare" in KMart in PA--though different bottle sizes were from
different locations).  The Fiji water was a on the light side
    Colorado and Idaho have light water, but in the -13 to -16 per mil
range for 18O, and we got them from Colorado and Idaho.  I haven't tried
fractionating my own yet--and I'm looking forward to other
suggestions...Of course, if you can deduct a water collection trip off
from your taxes....check out www.waterisotopes.org.  Gabriel J. Bowen
posted this earlier--they set up a water (precipitation) isotope
map--good stuff.

2.  H3+  factor--Not sure exactly how they calculate it, nor how they
apply it--though they do give a slope, ppm/nA (ppm vs area instead of
intensity).  If you play with your continous flow data, you'll see
changing the H3 factor and reintegrating doesn't affect the intensity of
masses 2 or 3 (raw data not changed), but the calculated areas are
changed.  I can't seem to find the math they use to correct for H3+ in
the manuals, though the GasBench manual does discuss how to do linearity
corrections on CO2 samples.  We run standards at the same (or close)
intensity as our samples for GCC and H-dev stuff (sorry, we don't do H2
equilibration with water)
    There was an earlier detailed discussion on the list about H3+
corrections in general, check out 6/11/04 in the archives: "H3+
correction".  Anyway, our H3 factor on the 253 has been holding around
15, on the high side but very stable.

take care

gerry


Anthony L. Michaud wrote:

>Hello everyone.
>
>Our lab is just starting up and one of my missions is to get going with H
>and O measurements from waters using the gasbench on a MAT 253. However... I
>have some questions that I can't seem to get sorted out:
>
>1) Concerning working standards for waters: Where to get antarctic/arctic
>waters?
>
>Is there any place in particular that will sell/give water for use as a
>light isotope ratio lab working standard? From old records in the archives
>it is clear that the heavy isotope working standard can be made by spiking
>water that is too light with a small amount of the heavy isotope (say D2O
>and/or 18-OH2 if needed). However, I don't know how labs get access to
>arctic or antarctic ice waters. Is it pretty much the case that labs send a
>note to their friends living way up north (or way down south) and ask them
>to mail a few liters of water their way?
>
>
>2) The H3 factor:
>
>There has been some discussion on the list about the H3+ correction already
>but does anybody know specifically how ISODAT calculates the H3 factor? I
>understand how it works and have read articles on this, but I find no
>documentation on how ISODAT specifically is determining the H3 factor. From
>the fact that there is a "starting value" for the H3 determination, it is
>clear that there is an iteration being done (perhaps to get the best
>precision for the results between the different intensity reference peaks
>used to determine the H3 factor), but I have not found any documentation on
>what exactly ISODAT is doing.
>Is this information proprietary? I would like to have a better understanding
>of what the software is doing.
>
>Many thanks for your help. I hope that I am not addressing something that
>has been extensively discussed and should be in the archives. If so, please
>point me there.
>
>Anthony
>
>
>