Regarding fractionation during storage for oxygen 18, the isotope lab at
the University of Washington had an infamous episode where many samples
were heavily fractionated after storage in a freezer within high density
polyethylene bottles.  See Stuiver et al., Quaternary Research, November
1995 for a discussion.  The problem may have been exacerbated by the
bottles being left out of the freezer (i.e. melted) for too long (several
weeks) but tests showed that fractionation occurred in the freezer as
well.  We had tested this in earlier years and found no problem.  After
much detective work by Tom Braziunas, it turned out that the bottles we
were using had much thinner walls than the orginals, even though they had
the identical catolog number and the same OUTSIDE diameter.  Evidently
there is some minimum wall thickness required to effectively stop
diffusion.  In short, HDPE is fine, but any particular bottle type needs
to be tested.

A solution adopted by many is to use glass instead, but the samples should
still be kept cold (and preferably frozen, but this has the potential
problem of glass fracture).  Also, the caps are generally plastic (though
usually less permeable than HDPE).

I'm sure that others on the list have specific preferred bottle brands
that have proven reliable.

Hope this helps.

Eric Steig

On Tue, 29 Sep 1998, Michael Lutz wrote:

> Dear Isogeochemers
>
> Do you collect and store water samples for DIC isotope and oxygen isotope
> analysis?  What sample containers do you use and why?
>
> I will be collecting hundreds of seawater samples for subsequent DIC
> isotope and water oxygen isotope analysis.  I am worried about the
> potential alteration of isotopic values during storage.  I have heard that
> screw capped bottles and even crimped blood serum bottles will eventually
> leak.  Is this folklore?  Can you recommend appropriate sample containers
> and tell me what their limitations are?
>
> Thank you,
> Michael Lutz
> Stanford University Stable Isotope Laboratory
>
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