Stable Isotope Geochemistry


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Nat Lifton <[log in to unmask]>
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Nat Lifton <[log in to unmask]>
Sun, 17 Nov 1996 23:59:11 -0700 (MST)
TEXT/PLAIN (37 lines)
Dear Kim - 

You can pass the gases over CuO at about 600 C one or more times to
oxidize the H2S to SO2. You can then separate the SO2 from the CO2 by
freezing the gases into a cold trap with LN, then subliming the CO2 from
the trap at -130 C using a pentane slush bath (for 5 to 10 minutes,
depending on how much CO2 you have). You'll probably have to repeat this
one or two more times on the resulting gas to get a really clean
separation, if you have a lot of SO2. You'll also have to be careful not
to pump on the pentane slush trap for too long (either with the vacuum
pump or by freezing the CO2 into a second trap) - 5 minutes seems to be a
good maximum time.  Even better would be to construct a variable
temperature trap per Des Marais (1978, Analytical Chemistry, v. 50, no. 9,
pp. 1405-1406) and sublime the CO2 at about -150 C for about 15 min. These
methods also almost totally eliminate water from the gases (the
equilibrium vapor pressure of water at -78 C [standard dry ice/alcohol
bath] is about 0.5 torr, but is several orders of magnitude lower at -130
to -150 C). The resulting CO2 and SO2 should then be suitable for del13C
and del34S analyses, respectively (although I've never analyzed for the
sulfur myself). I don't know about analyzing the H2S directly.

Good luck - 



                                NAT LIFTON
Geosciences Department				      PHONE: (520) 626-8053
University of Arizona				      FAX:   (520) 621-2672
Tucson, Arizona  85721  USA	  	     E-MAIL: [log in to unmask]