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Subject: H14CO3 stock solutions
From: "T.J. Evens" <[log in to unmask]>
Reply-To:T.J. Evens
Date:Wed, 22 Nov 1995 10:10:17 -0800
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There have been quite a few requests for me to post some of the
handling/storage problems associated with H14CO3 stock solutions, so here's
my best attempt:
 
        The primary source for the 14C we use is Du Pont (i.e. New England
Nuclear, or NEN), so some of these considerations might only apply to this
source.  I suggest that any of you who are using commercially prepared 14C
sources contact the supplier directly to obtain information pertinent to
their particular specs (we've gotten the most help from the techs who
actually prepare the solutions).
 
        The specific activity of any given stock solution is guaranteed for
only about 6 months IF you keep it at its shipping temperature (less time
if it's cycled between cold and warm--the solubility of CO2 in aqueous
media is negatively correlated with increasing temperature, so you are
effectively driving off a portion of the dissolved 14CO2 every time it's
warmed).  Since the stock solution is equilibrating with any air it comes
in contact with (even in buffered solutions), if you use your stock
solution a great deal of time (i.e. you do a good deal of 14C work) then
you'll lose quite a bit of activity to the atmosphere.  Of course, if you
work at room temperature with a stock solution that you're opening
constantly you could quite possibly lose a significant amount of activity
(a tech at Du Pont told us that we could expect about a 3% loss per day at
room temperature).  Our 14C is shipped at pH 8.8 (most I've seen are
shipped at ph 9.5!), so on addition to seawater of, say pH 8.2, there could
be quite a bit lost in gaseous 14CO2 in that initial equilibration.
 
        Of course, the specific activity of your media will be determined
by Rt values, but when deciding how much 14C to add to your test critters
it's probably good to realize you may not have as much 14C as you think you
do.
 
        And then there's the problem of unlabeled 14C in the stock solution
(I've heard values of up to 18 mM) that can increase the overall carbonate
carbon count in your media (which affects the carbon uptake    rate
equation).
 
        This points are by no means definitive, so if anyone has other
information to add please do so (I, for one, would be very interested in
any extra information that's out there).
 
        Thanks to Stephen Bates for reminding me of a great source of
information on all of this:  Measurement of primary production from the
molecular to the global scale:  a symposium held in La Rochelle, 21-24
April 1992.  Ed. by W.K.W. Li and S.Y. Maestrini.  Copenhagen, Internat.
Council for the Exploration of the Sea, ICES marine science symposia, 197.
(1993), 287 p.
 
Regards,
        T.J. Evens
 
*******************************************************************
                                     t.j. evens
                           department of biology
                          university of california
                           santa barbara, ca 93106
                               (805) 893-4319
                           [log in to unmask]
*******************************************************************

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