You might also try adding K2SO4 to the sample.  We use KHSO4 routinely for
trapping NH4 on paper disks.  The KHSO4 is still a strong acid and traps
NH4 well but will crystalize readily regardless of NH4 content.  When
crystalized is does not corrode the tin boats.  If you already have a
mixture of NH4 and H2SO4 then adding K2SO4 will produce a mixture that will
crystalize readily.  It does not appear to have any effect on the
combustion tube.

Remember that you will be analyzing total N, not just NH4.  There is a
possability that dry deposition has N in it.  You might want to diffuse
some samples to determine the actual NH4 15N.

At least one researcher I know has now worked out how to do natural
abundance 15N in waters and salt solutions by diffusion.

Paul.



At 09:37 AM 9/23/99 -0400, you wrote:
>Dear Listmembers,
>
>I am trying to analyze some atm NH4 samples for N-15 that were collected in
>denuders and washed out of the collector with sulfuric acid.  NH4 samples
>in HCl freeze-dry nicely, can be rehydraded with a drop of RO water and
>placed on chemsorb particles for analysis in a EA-CFIRMS.  Does anyone have
>a technique for analyzing NH4 samples trapped in sulfuric acid?  What
>happens if you inject conc sulfuric acid into the EA combustion column?
>
>Thanks for any help.
>
>Bill Showers
>----------------------------------------------------------
>William J. Showers
>Associate Professor
>Dept. of Marine, Earth, & Atm Sciences
>North Carolina State University
>
>(919) 515-7143 - voice
>(919) 515-7802 - fax
>[log in to unmask] - email
>
>



Paul D. Brooks.

Dept. ESPM-Ecosystem Sci.,
151 Hilgard Hall, MC 3110,
UC Berkeley, Ca. 94720-3110.

phone (510)642-3155
FAX   (510)643-5098 (to Att. Paul Brooks)