Dear Paul

Another method for removing NH4+ or NO3- from water (fresh or
seawater) is by steam distillation.  To my knowledge, this is the
most frequently used method cited in the literature.  The method was
first developed by Bremner in 1965 (see below) and has been modified
by Velinsky et al. (1989) for extracting DIN from natural waters at
natural abundance levels (as low as 5 uM NH4-N) for isotopic analysis.

Other methods use solvent extraction (Dudek et al., 1986) or mercury
precipitation (Fisher & Morrissey, 1985), but these risk isotopic
fractionation by incomplete recovery of ammonia.  To my knowledge
these methods have only been used in enrichment experiments.  Steam
distillation have been shown to provide 100% recovery at low DIN
concentrations, thereby eliminating isotopic fractionation.  The
distillation method also use Devarda's alloy for the conversion of
nitrate to ammonium.

Useful references:

Fisher & Morrissey.  1985.  A new method for the recovery of ammonium
from natural waters for measurement of 15N composition in isotope
dilution experiments.  Mar. Chem. 16: 11-21.

Dudek et al.  1986.  Recovery of ammonium nitrogen by solvent
extraction for the determination of relative 15N abundance in
regeneration experiments.  Mar. Chem. 18: 59-69.

Velinsky et al.  1989.  Determination of the isotopic composition of
ammonium-nitrogen at the natural abundance level from estuarine
waters.  Mar. Chem. 26: 351-361.

Bremner.  1965.  Determination and isotope ratio analysis of
different forms of nitrogen in soils: I. Apparatus and procedure for
distillation and determination of ammonium.  Soil Science Society
Proceedings 29: 504-507.

With the steam distillation method, ammonium can by precipitated as
ammonium sulphate or ammonium chloride, exchanged onto an ion
exchange resin, or captured on an acidified filter paper (micro
diffusion).  The salt, resin, or filter can then be prepared using
conventional methods for ANCA-MS (without the simulatneous
determination of carbon of course).

Hope this helps.

Regards
AJ



> 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
> #########################################################################
> AJ Smit                        Tel.: +27 21 650 3402
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