1070-4272/05/7811-1864+2005 Pleiades Publishing, Inc.
Russian Journal of Applied Chemistry, Vol. 78, No. 11, 2005, pp. 1864!1868. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 11,
2005, pp. 1895!1899.
Original Russian Text Copyright + 2005 by Rutkoviene, Grazuliaviciene, Cesoniene, Kusta.
OF CHEMISTRY AND TECHNOLOGY
Determination of Nitrate Concentration in Natural Waters
V. Rutkoviene, V. Grazuliaviciene, L. Cesoniene, and A. Kusta
Lithuanian Agricultural University, Kaunas region, Lithuania
Received August 11, 2005
Abstract-Three methods of determining nitrate ion concentration in natural waters, namely, the potentio-
metric method, the spectrophotometric method using sodium salicylate, and the spectrophotometric method
using 4-fluorophenol after distillation, are compared. Factors influencing the accuracy and reproducibility of
the measurements are determined, and the statistical evaluation of the results obtained is given.
Nitrates are an inherent component of natural water.
The amount of nitrates in surface waters is usually in-
significant, but their concentration in subsoil waters is
high . In rural places, the inhabitants most often
use water from dugout wells. Water enters dugout
wells from subsoil aquifers which are the least pro-
tected from the surface pollution. Therefore, it is
extremely susceptible to chemical and microbiological
pollution . The subsoil water is most often polluted
with nitrates, and their concentration exceeds the
background concentration in the nature .
An increase in the water pollution with nitrates
makes it necessary to monitor the quality of potable
water, to estimate the influence of the environmental
factors on the water quality, and to determine how
these compounds enter the natural water sources.
Reliable and efficient methods of determining the ni-
trate concentration in water are necessary for these
studies. Since the concentrations of nitrates in natural
waters are essentially different, it is important to select
procedures suitable for a wide concentration range.
Potentiometric, voltammetric, polarographic, and
spectrophotometric methods are used for determining
nitrate concentrations [6, 7]. The spectrophotometric
methods are based on the reaction of nitrates with
certain reagents and on the measurement of the optical
density of a light-absorbing solution of a colored
compound formed in the reaction. Phenoldisulfonic
acid, sodium salicylate, 4-fluorophenol, and 2,6-di-
methylphenol are used to obtain colored compounds
. The spectrophotometric methods of determin-
ing nitrate concentrations with phenoldisulfonic acid
and sodium salicylate are used in the analysis of pot-
able and surface waters. These methods allow the ni-
trate concentrations of 2.0 and 25 mg l
to be determined in an undiluted sample. In the case of
high nitrate concentrations, samples must be diluted,
which can affect the accuracy of the measurements.
The nitrate concentrations of up to 250 mg l
water are determined by the spectrophotometric
method using 4-fluorophenol without diluting a water
When selecting a method, we must take into ac-
count not only the nitrate concentration, but also the
presence of other ions in water under study. The pres-
ence of chlorides, nitrites, sulfates, and other ions can
affect the accuracy of the measurements.
The accuracy of the method depends on the charac-
teristics of devices in use. For example, when deter-
mining the nitrate ion concentration potentiometrical-
ly, the sensitivity and selectivity of the electrodes in
use determine the accuracy of the measurements to
a large extent.
The aim of this study was to assess the expediency
of using various methods of determining nitrate con-
centrations in natural waters and to examine how
specific features of a particular method and concomi-
tant ions affect the accuracy and reproducibility of
We determined nitrate concentrations by the fol-
(I) Spectrophotometric method with sodium sali-
cylate [6, 8]. To construct a calibration plot, we used
reference solutions with nitrate concentrations from
0.1 to 10 mg l
. We measured the optical density of
the solutions using a Genesys 5 spectrophotometer
at a wavelength of 410 nm. We used cells with a layer
thickness of 1 and 5 cm.