Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 221

10.0 1.86

1.08 c

Daz ′
1.0

2.48 e

1.12

1.05 c 202.5 e

10.0 1.56

Unpolluted river water
humic acid-inorganic
salts NO 3 -N by
polarography
1.170

1.77 c 3.15 a

1.69 1.77

a Addition of exact amount of silver sulphate to precipitate chloride with no excess silver
b Addition of sulphamic acid (final conc, in sample approximately 20mg L −1 )
c Treatment with Amberlite XAD-2 resin
d Addition of saturated silver sulphate (1ml to 10ml sample). Not recalibrated. Addition of 2mol
L −1 acetic acid to sample (0.09ml per 30ml sample). Not recalibrated
e Calibrate for presence of 3ml saturated silver sulphate and 0.09mol L −1 acetic acid in 30ml
sample
f Daz—a commercially available household detergent
Source: Reproduced with permission from Elsevier Science [468]

nitrate could be quantitatively determined down to the µg L −1 level. The method is also
applicable to nitrite, after separation of nitrate ions, which can be performed by ion
exchange in the alkaline pH range.
Wolff et al. [471] have determined nitrate in water samples by isotope dilution analysis
using a small thermionic quadruple mass spectrometry. The isotope dilution experiments
were carried out using the Institute for Reference Materials and Measurements' 15N-
enriched nitrate spike reference material IRMM-627. Nitrate was isolated from the matrix
by precipitating it as nitron nitrate, from which emission of negative thermal nitrite ions
was found to be best. The ions were produced in the ion source of a small, low-cost, easy-
to-handle thermionic quadruple mass spectrometer equipped with a secondary electron
multiplier coupled to an ion counter. The procedure developed was applied to the
measurement of nitrate in a certified reference material (simulated rainwater, CRM 409
from Community Bureau of Reference), in sparkling mineral water and in tap water.
Results were compared with those obtained using ion chromatography. Good agreement
(within 1%) was found between the concentration determined by isotope dilution mass
spectrometry, the values from ion chromatography, and the certified value. The procedure
developed allowed accurate and traceable determinations of nitrate in water samples, with
an expanded uncertainty (coverage factor k=2) of 2-5% and the detection limit was found
to be 2µmol kg −1 .
The application of thermionic quadruple mass spectrometers has also been discussed in
Heumann et al. [472] and Rever et al. [473].