Alice

You would need to check that the potential decomposition products of
sodium azide do not include any of the dissolved gases you want to
measure (N2?).

Tim H.E. Heaton

NERC Isotope Geosciences Laboratory 
British Geological Survey
Keyworth, Nottingham NG12 5GG, England
(www.bgs.ac.uk/nigl/index.htm)

Tel. +44(0)115 936 3401
Email: [log in to unmask]


-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On
Behalf Of Alice Chang
Sent: 12 August 2008 19:37
To: [log in to unmask]
Subject: [ISOGEOCHEM] sodium azide preservative

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

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