Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 223

down to 0.1mg L −1 nitrate in water, without interference from other ions associated with
potable, pond, river and stream water.
Detection of the separated peaks was achieved using a Pye LC-UV variable
wavelength ultraviolet detector fitted with a 8µL flow cell and set at 265nm. The
chromatographic system consisted of Partisil 10µm SAX column, and a mobile phase
consisting of 10 −3 M potassium hydrogen phthalate (pH 3.95) in deionised water.
In Fig. 2.30 is shown a calibration curve obtained for a set of nitrate standard solutions.
This was linear (correlation coefficient=0.9958) and was defined by the equation
Using this calibration line a series of water samples was studied and
the nitrate levels measured.
Schroeder [476] has determined nitrate in non saline waters and wastewaters by high
performance liquid chromatography using aqueous phosphoric acid/sodium dihydrogen
phosphate as the mobile phase and UV detection. The optimum nitrate concentration was
0.3-3mg L −1 as nitrate with a linear response for <3mg L −1 as nitrogen. Relative standard
deviations in the optimum range were <1%, and the detection limit was 0.0007mg L −1 as
nitrogen. Various potential interferences, including nitrite, are separated from the nitrate
on the high performance liquid chromatography column.
The application of this technique is also discussed under multianion analysis in
sections 13.1.1.3, 13.1.1.4 and 13.1.1.5.
2.62.15 Ion exchange chromatography
Sherwood and Johnson [477] have described an ion exchange chromatographic
determination of nitrate and amperometric detection at a copperised cadmium electrode.
The chromatograms obtained in this procedure resolve nitrate from dissolved oxygen.
2.62.16 Micelle chromatography
The application of this technique is discussed under multianion analysis in section
13.5.1.2.
2.62.17 Gas chromatography
Christensen and Tiedje [478] used a denitrifier (Pseudomonas chlororaphis) in
determining nitrate to nitrite at sub-ppb levels in non saline waters. The denitrifier
reduces the nitrous oxide to nitrogen and does not reduce the nitrous oxide any further;
the released nitrous oxide is measured with a 63 Ni electron capture gas chromatograph
detector, with very little background interferences. The optimum measurement range was
from 0.5 to 50µg L −1 of nitrate nitrogen and the detection limit was 0.2µg L −1 of
nitrogen.
2.62.18 Miscellaneous
Kiang et al. [474] reduce nitrate with nitrate reductase and nitrite with nitrite reductase
using an air gap electrode to monitor the ammonia produced by the reduction of nitrate.