Chemistry Reference
In-Depth Information
organic matter.
Absorbance measurements were made at 210nm with a Cecil Instruments 272
ultraviolet visible spectrophotometer, fitted with a 10nm path length Spectrosil silica
micro-flow cell (Type 75, Starna Ltd). The output trace was monitored on a Smiths
Industries Servoscribe recorder. A Chemiab Instruments 15 channel peristaltic pump and
40 position autosampler were used. The continuous-flow manifold is depicted in Fig.
7.10.
Excellent precision is obtained by this procedure (Table 7.13).
The dialysis membrane minimised the ultraviolet absorption interference from organic
matter present in water, as the efficiency of transfer
Table 7.13
Precision of analytical results
Standard deviationa/mg
L
−1
of N
Mean concn. found/mg
L
−
1
of
N
Solution
Sw.
S
b
S
t
0.00µg mL
−1
of N
0.032 (5)
-
-
0.031
2.00µg mL
−1
of N
0.10(5)
ns(4)
0.11(8)
2.30
15.00µg mL
−1
of N
0.17(5)
ns(4)
0.17(8)
14.95
18.00µg mL
−1
of N
0.16(5)
0.25 (4)
0.30 (8)
18.04
River Dove water
0.061 (5)
ns(4)
0.071 (7)
4.58
River Dove water
+
9.55µg mL
−1
of N
0.11 (5) ns(4) 0.16(6)
14.08
b
a
Numbers in parentheses correspond to the number of degrees of freedom, ns indicates that the
result is not statistically significant at the 0.05 level of significance
b
Recovery of added nitrate was 99.48%
Source: Reproduced with permission from the Royal Society of Chemistry [49]
Table 7.14
Comparison of methods for the determination of nitrate in some coloured raw
Pennine water samples
Nitrate concentration/mg
L
−1
of N
Sample
no.
Apparent
colour
A m
−a
Reduction
method
Manual UV method
b
Proposed method
c
1
10.0
0.81
2.19
0.85
2
12.2
0.64
2.19
0.65
3
10.4
1.33
2.98
1.34
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