Hello David,

(warning to the squeamish, stop right now)

D/H and 18O/16O in mouse blood would be done the same way as those 
isotopes in human blood--by headspace equilibration.  This is a routine 
measure in nutrition research that allows the determination of energy 
expenditure after a dose of double labelled water.

This procedure is performed in the water-bearing fraction of blood--serum or 
plasma, depending on how it is collected.  The proteins and electrolyte 
components of cells interfere so whole blood is not an option.  Freeze dried 
blood will give you great 15N/14N and 13C/12C but not the water isotopes.

This procedure is usually run with 13mL vials that require a minimum of 500uL 
plasma or serum in triplicate for the best results.  Humans have plenty of 
blood to enable several collections over two weeks for this measure.  This 
means 2mL serum/plasma and therefore the blood of a whole adult mouse 
collected by cardiac puncture.   The same vials can be used for both D/H and 
then 18O/16O.

One can make the same determination with urine, but take it from those of us 
who have tried, getting clean mouse piss is not so easy...

So for small animals, you must use the pyrolysis of the serum/plasma and hope 
that you can get enough injections for a decent value before something clogs 
due to the proteins. Good luck!

Irene Ellis
Astimex Scientific




On Wed, 11 Jul 2007 20:41:35 -0400, David Mrofka 
<[log in to unmask]> wrote:

>Dear List Members,
>
>A colleague of mine is interested in determining H and O values from mice
>blood.  I was thinking that O could be done by pyrolysis from freeze-dried
>blood.  How about hydrogen...any reason that the water H in blood would not
>equilibrate with head gas and be able to be determined in a gas bench?  Any
>advice on either idea would be appreciated.
>
>Dave Mrofka
>Earth Sciences
>UC Riverside
>
>