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the microconstituents (200, 300 and 600 ppt for nitrite, fluoride and phosphate,
respectively) enabled their determinations at low parts per billion concentrations in
instances when the concentrations of sulphate or chloride in the samples were higher than
1000 ppm. Although in such situations the load capacity of the capillary isotachophoresis
column was not sufficient to provide the quantitations of the macroconstituents, the
capillary isotachophoresis sample cleanup enabled the capillary zone electrophoresis
determinations of the microconstituents present in the samples at 10
5
-10
6
-fold lower
concentrations. Experiments with samples of such extreme compositions showed that
anionic impurities from the capillary isotachophoresis electrolyte solutions transferred
together with
Table 14.5
Determinations of anionic macro constituents present in model mixtures
Sulphate
(mg L
−1
)
Nitrate
(mg L
−1
)
Chloride
(mg L
−1
)
Sample
Taken
UP
Titrimetry Taken ITP
Spectro-
photometry
Taken ITP Titrimetry
A
40.0
49.7
32.7
14.0 14.4
14.3
25.0 25.4
29.9
B
100.0 100.5
103.7
30.0 30.2
24.2
50.0 49.8
47.5
C
150.0 149.6
-
45.0
a
44.0
75.0
a
83.7
a
Mixed zone of nitrate and chloride for the column used
For further details see notes in Table 14.4 and the text
Source: Reproduced with permission from Elsevier Science [47]
the analytes into the capillary zone electrophoresis column are probably the main
hindrances in extending this dynamic concentration range by decreasing the limits of the
detection to a level associated with the noise characteristics of the conductivity detector.
14.6.2
Aqueous precipitation
14.6.2.1
Chloride and fluoride
Zelenski
et al.
[47] applied column coupling capillary isotachoelectro-phoresis to the
determination of chloride and fluoride in rainwater.
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