Chemistry Reference
In-Depth Information
+2µmol L
−1
NO
3
-
5
3.47
3.77
94.5
B. Jacks Creek
0 5
0.918
17.9
+1µmol L
−1
NO
3
−
5
1.87
4.01
95.2
+2µmol L
−1
NO
3
-
5
2.96
3.50
102
C. Peat bog pore
0 2
0.776
1.18
+1µmol L
−1
NO
2
-
2
1.74
3.54
96.4
+2µmol L
−1
NO
2
−
2
2.90
2.12
106
D. Neuse River
0m 4
8.07
2.14
+5µmol LL
−1
NO
3
-
4
13.1
3.79
101
+10µmol L
−1
NO
2
-
4
18.1
1.22
100
E. Neuse River
12 4
0.160
12.5
+1µmol L
−1
NO
2
-
4
1.11
8.64
95.3
+2µmol LL
−1
NO
3
-
4
2.12
2.45
98.0
F. Pamilco pore H-
2
O
0 3
1.07
1.62
+0.5µmol L
−1
NO
2
3
1.59
2.18
104
+1µmol LL
−1
NO
3
−
3
2.01
0.860
94.0
Source: Reproduced with permission from Elsevier Science [120]
nickel for 30min and then stirring for 90min at 90°C, to reduce nitrate to ammonia. The ε
value is 8500 at 210nm and 4100 at 220nm. Beer's law is valid up to 10mg L
−1
at 210nm
and up to 15mg L
−1
at 220nm. The standard deviations for a sample containing 17.4mg
L
−1
of nitrate were 0.3 and 0.5mg L
−1
at 210 and 220nm respectively. No systematic
errors were detected.
Previous ultraviolet methods for determining nitrate have attempted to allow for humic
acid interference [123-126]. However, with the exception of Morries [126] these
methods of allowance are inaccurate at humic acid concentrations above about 3.5mg
L−1. Unfortunately, none of these methods have attempted to make any allowance for
ultraviolet absorbing pollutant organic compounds or interfering inorganic ions. Thus
their applications to water analyses other than for relatively unpolluted fresh waters is
open to question.
Brown and Bellinger [127] have proposed an ultraviolet technique that is applicable to
both polluted and unpolluted fresh and some estuarine waters. Humic acid and other
organics are removed on an ion exchange resin. Bromide interference in seawater
samples can be minimised by suitable dilution of the sample but this raises the lower
limit of detection such that only on relatively rich (0.5mg L−1 N
O
3
N) estuarine and
inshore waters could the method be used. Chloride at concentrations in excess of
10,000mg L−1 do not interfere.
The method is either not affected by or can allow for interference from phosphate,
sulphate, carbonate, bicarbonate, nitrite, coloured metal complexes, ammonia dyes,
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