Hello Isogeochemists,

We are having a dilemma choosing a suitable preservative--mercuric
chloride versus sodium azide--for seawater samples that will be analyzed
for DIC and a variety of dissolved gases. The preservatives are used to
prevent bacterial growth or anything that can affect the character of the
seawater when it is collected. Diluted mercuric chloride is currently
used, as that is the protocol. However, our new labs are moving towards
zero-Hg tolerance (or as low as possible), and HgCl2 presents a
contamination source to colleagues doing Hg analyses. Azide is the
alternative, but we have never used it. In concentrated form, azide
appears to be reactive (explosive) with heavy metals and forms toxic fumes
in contact with acids.

What concentration of sodium azide solution is usually used that is safe
enough to prevent reactions with metals or acids? We don't want to be
rinsing and diluting our water samples post collection because that would
drastically affect the water's chemical make-up. For DIC analysis via
coulometry, the water samples will be reacted with dilute phosphoric acid,
and we don't want any adverse effects.

Thanks.
Alice



-- 
Alice S. Chang
Post-doctoral Fellow
School of Earth and Ocean Sciences
University of Victoria