once more a comment to O-18 in Nitrate.
As Barbara Kornexl (UFZ Leipzig-Halle, Germany) already mentioned that
on-line technique (CO) is used for O-18 measurements of O-bearing samples,
we also use the off-line technique reported by Silva and Len Wassenaar (see
comment from Bernhard Mayer) on silver nitrate converted from natural water
samples. Revesz et al (Anal. Chem 69: 4375-80) work with KNO3+C and
recalculating the O-fractionation.
Another technique we tried deals with guanidine hydrochloride as reactant
for off-line preparations (K. Brauer & G. Strauch: An alternative procedure
for the O-18 measurement of nitrate oxygen, sub to Chem.Geol.)
Reproducibility is 0.2 o/oo based on KNO3-lab std. and IAEA-N3.
The problem (mentioned by Bernhard) is to get a pure non-contaminated
substance containing all the oxygen from the nitrate sample. The
conversion via various steps with ion exchange resins and
neutralisation/separation to silver nitrate seems to be the most commonly
used method. However, with the most pitfals!
With our off-line silver nitrate technique we can report a reprod. of 0.4
o/oo from lab standard measurements (including separation of nitrate from
water sample, converting to CO2) for about 1 year.
Moreover, we use the O-18 nitrate method for groundwater, soilwater,
porewater from lysimeters having sulfate content mostly <1g/l, DOC <10 mg/l.
Am/Um 12:08 04.08.99 +0200 schrieben Sie:
>Who out there is out there doing 16O-18O ratios on nitrate? if so what's the
>latest technique and easiest ?
>Someone asked me for this information, as we don't do it here yet I would
>be interested to find out how and what are the pitfalls.
>Samples they are thinking of are soil-water samples, at natural abundance
>levels. It has some interesting potential....
>I would be most grateful for all suggestions, comments, references etc...
>Thanks in advance for any assistance........
>Long live isogeochem....