We found that anion exchange resins were no more satisfactory than ammonia
conversion methods in extensive work on highly organic soils over many years.
I must add, however, that we have not tried Carol Kendall's method for using
anion exchange resins.  We, therefore, developed a method which derivatises
nitrate as a dye molecule, specifically targetting the nitrate chemically.  It
works reliably and accurately for us in highly organic soils and eutrophic
waters.

It is clear to me that Carol and I need to compare methods on the same samples
having a range of organic nitrogen contents.  It is the organic nitrogen
contamination which is the chief concern.  It is unlikely, in general, that any
one method will be appropriate for all types of samples, and on those grounds I
suspect that her resin method will work beautifully up to some yet-to-be
determined amount of organic N.  Our method, unfortunately, won't allow you to
measure 18-O of nitrate......tradeoffs everywhere.

Carol, shall we follow up on this collaboratively?

Cheers to all,

Linda Handley



Jim Karagatzides wrote:

> Dear Isogeochemists,
>
> I'd like to use the USGS anion resins for N-15 and O-18 analyses (described
> in Chang et al., 1999, Can J Fish Aquat Sci and Silva et al., 2000, J
> Hydrol) and am looking for advice or comments from experienced users.
>
> I will be in a fairly remote study area on the west coast of Vancouver
> Island, B.C., Canada but have occassional access to a field house to do the
> lab work. While I will analyze streamwater, forest throughfall and oceanic
> waters, my main goal right now is to measure N-15 in soil moisture
> collected with porous-cup lysimeters under vaccuum. I have some preliminary
> background levels and it appears to me that I have fairly low nitrate
> concentrations (summer average of about 100 ug/L; range 10 - 200 ug/L) but
> high DOC (40-90 mg/L) and "high" Cl (50 - 300 mg/L, depending on location
> and depth in soil) from sea spray. I will use the 5ml columns with the
> cation column to minimize DOC accumulation on the anion column. And, I
> presume I will have to use multiple anion columns for each sample because
> of the high Cl levels and low NO3.
>
> Has anybody used the anion columns to measure N-15 in nitrate of soil
> moisture? Even though I will be working in the wettest part of Canada in
> highly saturated soils, I'm developing an uneasy feeling that I may not be
> able to use the method since I have low NO3 but high Cl and DOC levels (?).
>
> Thank you for any comments and advice.
>
> Jim
>
> ============================
>
> Jim Karagatzides
> Department of Geography
> Queen's University
> Kingston  ON  K7L 3N6
>
> Tel: 613-533-6000 x77831
> Fax: 613-533-6122  or 6617