Chemistry Reference
In-Depth Information
eluent is the most suitable when simultaneous determination of fluoride, chloride, nitrite,
bromide, sulphite, nitrate, sulphate and phosphate is required or when the sample is
considered to contain all of these ions. Further studies were therefore made using this
eluent.
Fig. 12.27(a)(b) shows that an optimum eluent for the determination of anions can be
selected, and that information to determine the interfering ions and the best conditions
can be obtained.
Using this procedure, except for nitrite, the coefficient of variation for each ion was
less than 5%, and reproducibility was relatively good (Table 12.11). The peak height of
nitrite was elevated as the number of sample injections were increased, and after nine
tests the increase in peak height was as high as 20%.
The separation of chloride, nitrite, nitrate, sulphite and sulphate ions in an actual
rainwater sample was repeatedly carried out using the procedure. Table 12.12 shows the
results, which indicate that the peak height of nitrite tended to increase as the number of
times the determination was repeated, showing a coefficient of variation of 13.3%. The
coefficient of variation of other anions was less than 10% as was the reproducibility test
of the standards.
The detection limit of each ion was obtained from the peak of the chromatogram and
the noise of the base line when 100µL samples containing fluoride (0.1mg L
−1
), chloride
(0.2mg L
−1
), nitrite (0.5mg L
−1
), nitrate (1mg L
−1
), sulphite (5mg L
−1
) and sulphate
(3mgL
−1
) were used.
Table 12.12
Reproducibility of anions in actual rainwater samples
Cl
−
NO
2
−
NO
3
−
SO
3
2−
SO
4
2-
Ion no
1
2.47
0.78
0.43
1.04
0.83
2
2.32
0.79
0.48
1.09
0.84
3
2.24
0.87
0.48
1.31
0.87
4
2.18
0.95
0.42
1.15
0.86
5
2.11
0.95
0.38
0.98
0.81
6
2.15
0.97
0.46
1.09
0.81
7
2.15
0.99
0.49
1.09
0.86
8
2.10
1.13
0.48
1.20
0.83
9
2.12
1.13
0.46
1.20
0.86
X
2.20
0.95
0.45
1.12
0.84
CV%
2.5
13.3
8.1
8.8
2.7
Source: Reproduced with permission from Elsevier Science [59]
When the detection limit was twice the signal to noise ratio of the base line these limits
were 0.01mg L
−1
for fluoride, 0.02mg L
−1
for chloride, 0.05mg L
−1
for nitrite, 0.0mg L
−1
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