Chemistry Reference
In-Depth Information
first passed through a column of cation exchange resin. The first 20ml of effluent is
discarded and the next portion is used.
Table 2.51
Effect of co-existing ions
Ion
Added
as
Conc.
(mg L
−1
)
Ion
Added as
Conc.
(mg L
−1
)
Found
SO
4
2−
(mg L
−1
)
Found
SO
4
2−
(mg L
−1
)
K
+
5×10
-4
None
-
-
5.0
KCl
5.1
Cl
−
5×10
-4
Na
+
1×10
−3
KCl
5.1
NaCl
5.0
KHCO
3
1×10
−4
5.0
NH
4
Cl
5×0
−4
5.0
HCO
3
−
NH
4
+
NO
3
−
KNO
3
1×10
−4
5.0
Mg
2+
MgCl
2
.6H
2
O
1×10
−4
5.0
H
2
P
4
−
KH
2
PO
4
1×10
−4
5.1
Ca
2+
CaCl
2
.2H
2
O
5×10
−5
4.9
Na
2
SiO
3
5×10
−4
Fe
3+
FeCl
3
.6H
2
O
5×10
−4
0.0
5.0
SiO
3
2−
Source: Reproduced with permission from Elsevier Science [769]
Van Staden [770] has also described an automated turbidimetric determination of
sulphate in non saline waters by flow injection analysis. One sampling loop of a two-
position sampling valve is used to sample an alkaline buffer/EDTA solution, while the
other loop is used alternately to sample water, thus avoiding acidification of water
samples and lessening baseline drift. Residual precipitate is redissolved from the walls of
the flow cell. The coefficient of variation for standard sulphate solutions and for water
samples, containing 50-140mg L
−1
sulphate, is less than 0.95%. The procedure is
suitable for carrying out 60 analyses per h.
A typical representative strip-chart recorder output obtained by this method at a
sampling rate of 60 actual water samples per h is illustrated in Fig. 2.51. The negative
peaks between samples are due to the alternate sampling of alkaline buffer-EDTA
solution. Carry-over from one sample to another is negligible. No baseline drift was
experienced.
Krug
et al.
[771] have used flow injection analysis for the turbidimetric determination
of sulphate in non saline waters. They give details of equipment and procedures for a
flow injection system with automated alternating streams of reagents for the turbidimetric
determination of sulphate. The method is suitable for 120 samples per h with a relative
standard deviation less than 1% for sulphate concentrations in the range 1-30mg L
−1
.
Samples are injected into an inert carrier stream which is mixed with barium chloride
to form a barium sulphate suspension. The range of the method can be extended to low
concentrations by continuously adding sulphate to the sample carrier stream. System
performance is improved by automatic alternate pumping of the reagent stream and an
alkaline EDTA solution at high flow rate. All operations are controlled by an
electronically-operated proportional injector-commutator.
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