Chemistry Reference
In-Depth Information
0.5
10
0.197
2.1
1.0
10
0.343
1.0
2.0
10
0.619
0.61
0.0
1
0.006
36
2.0
1
0.070
0.82
5.0
1
0.167
1.5
10
1
0.330
0.30
20
1
0.649
0.15
Source: Reproduced with permission from Elsevier Science [120]
Mean absorbance and coefficient of variation for potassium nitrate standards analysed in
triplicate by this method are given in Table 3.8. Absorptivity (ratio of absorbance to the
product of optical path length and concentration) was 0.029 and 0.032 for the 10 and 1cm
optical paths, respectively.
Suspended solids and coloured organic matter interfere with the analysis and should be
eliminated by filtration and precipitation as described in the procedure. To assess the
extent to which other components of non saline waters affect the accuracy of the
proposed method, known amounts of nitrate were added to a number of sample types
with salinities of 0-12% (Table 3.9). Recoveries for these nitrate-spiked samples were
94-106%.
Mubarek
et al.
[121] showed that the loss of nitrate in the presence of chloride in the
phenoldisulphonic acid spectrophotometric method is eliminated by complexing the
chloride with mercuric ion.
3.20.2
Ultraviolet spectroscopy
Ultraviolet spectrometry has also been used to determine nitrates. In a method for
determining high levels of nitrate described by Mertens and Massart [122] the sample,
diluted to contain 0.5-1mg L
−1
nitrate is acidified, filtered through a 0.5µm filter and the
extinction measured against a blank at 210-220nm. The concentration of nitrate is
obtained from a calibration graph. Interference from chloride, bromide, organic matter,
carbonate, bicarbonate and nitrite is largely removed by using as blank a solution
prepared by boiling 10ml of the sample with 0.5g Raney
Table 3.9
Recovery of known additions of NO
2
−
nitrite
Salinity PP 10
3
n
Concn mean
(µmol L
−1
)
CV(%) % recovery
Sample
A. Pamlico River
8 5
1.58
6.71
+1µmol L
−1
NO
3
-
5
2.55
2.20
97.0
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