Hi Carol, Your method sounds very intersting and what a great idea to use
sugar!  I will have to pay a visit to your lab someday to see this all in
operation.  Thanks for taking the time to send it to me in such detail.

 Apparently a group in Woods Hole has just had a diffusion method for NO3 in
seawater accepted for publication.  I can send you details if you are
interested.

We are now very pleased with our 20/20, we are now running 200-400 C+N's a
week at natural abundance.

Got to run, I am sure we will be in touch.

Paul.


At 15:45 7/11/97 -0700, you wrote:
>Hi Paul:  Steve Silva and I have been happily using our resin column method
>to collect NO3 from dilute waters for d15N and d18O for many years now
>(Silva et al, in review).  For the last year, we have been saving time by
>analyzing the nitrate using our Optima EA to run the d15N by continuous
>flow, instead of doing sealed-tube combustions of the resultant AgNO3.
>
>After we elute the NO3 from the resin column with HCl, we neutralize the
>eluant with Ag2O, filter out the AgCl, freeze dry the remaining solution to
>produce AgNO3, add a little water, pipette aliquots into 2-4 silver boats,
>freeze dry the boats in a little loosely-covered rack, fold and crush the
>boats, and then load them into the EA carousel. Silver boats, instead of tin
>boats, are used for combustions because AgNO3 readily corrodes tin foil.
>However, when AgNO3 is combusted in silver boats, we would sometimes get
>weird drifting d15N values that suggested combustion problems.  Long-time EA
>users suggested that we needed to add something to the nitrate to improve
>the combustion efficiency, and we tried CuO, VO5, and other materials.
>
>A "sweet solution" for this troubling analytical problem has been to add
>table sugar directly into the boats containing the nitrate samples, with 2
>mg of sugar adequate for samples producing up to 20 umoles of N2, although
>we normally run much smaller samples.  We find that addition of table sugar
>produces consistent and accurate d15N values for both KNO3 and AgNO3, with
>analytical precisions of 0.1 to 0.2 permil.  The only problem we have found
>with using silver boats has been that the silver boats melt instead of
>flashing, which can make ash removal difficult or impossible.  In addition,
>some samples with very enriched 15N values appear to produce temporary
>memory effects that may be related to the lower combustion temperature.
>
>--Carol
>
>
>
>>Dear list members,
>>
>>Does anyone know of a method for measuring 15N at natural abundacne
>>precision using a continuous flow  C/N analyzer connected to a isotope ratio
>>mass spectrometer (ANCA system)?  There are severasl published methods
>>(including our own) for converting enriched NO3 to NH3 with Devarda's alloy,
>>diffusing it onto acidified paper, putting the paper in tin capsule and
>>burning it in the C/N analyzer.  However, I do not know if this or a similar
>>procedure has ever been thouroughly evaluated for natural abundance 15N
>>measurements.
>>
>>I would appreciate any information on any experiences anyone has had trying
>>to use this method, or any method to analyze naural abundace 15N nitrate
>>using an ANCA system.
>>
>>Thanks,
>>
>>Paul D. Brooks.
>>
>>
>>########################################################################
>>Paul D. Brooks, Spectroscopist,
>>Dept. ESPM,
>>151 Hilgard Hall,
>>UC Berkeley, Ca. 94720-3110
>>USA.
>>
>>email [log in to unmask]
>>
>>phone: (510)642-3155
>>FAX:   (510)643-5098
>>#########################################################################
>>
>>
>
>


########################################################################
Paul D. Brooks, Spectroscopist,
Dept. ESPM,
151 Hilgard Hall,
UC Berkeley, Ca. 94720-3110
USA.

email [log in to unmask]

phone: (510)642-3155
FAX:   (510)643-5098
#########################################################################