Chemistry Reference
In-Depth Information
described by Technicon for the measurement of alkalinity. A 15×2.0mm flow cell and a
550nm filter were used. The electronic gain on the colorimeters can be varied from 0 to
100. For the purpose of comparison the gain was set at 10.0. The Coulter Kem-O-Lab
(IKL) was used following manufacturers' recommended procedure for measuring
alkalinity. The IKL automatically takes a standard volume of sample and mixes it with
0.5ml of distilled water and 1.0ml of methyl orange reagent. Measure the absorbance
with a 2cm flow cell and a wavelength of 540nm 12min after the reagent is added.
The titration was performed with a Brinkman pH meter, to monitor the pH and a
Dosimat E535 (Brinkman) to deliver the titrant. Titrate a 25ml
Table 2.4
Comparison of results of alkalinity tests by titration
Technicon AutoAnalyser
mg L
−1
Kem-O-Lab
Coulter
mg L
−
1
Sample
Titration
mg L
−1
Std dev
a
Std dev
a
Mean
std dev
Mean
Mean
1103
26.1
0.9
26.5
0.5
25.4
0.2
1111
44.6
0.3
44.1
0.5
44.3
0.1
1112
14.9
0.7
15.2
0.9
13.9
1.2
1113
13.4
0.7
13.8
1.3
13.4
2.3
1114
20.3
0.7
10.6
0.6
18.7
1.5
1116
56.6
0.3
57.3
0.3
57.8
0.9
1118
147
0.3
144
3.5
141
1.4
1119
104
0.3
102
3.6
104
2.9
1120
226
1.6
259
2.4
264
1.2
Av
0.6
1.4
1.3
a
Based on five measurements for each determination of mean or standard deviation
Source: Reproduced with permission from the American Chemical Society [152]
sample to a preliminary endpoint of pH 5.6 with 0.02N sulphuric acid. With this volume
of titrant as a measure of the approximate alkalinity, the sample was further titrated to a
final endpoint based on the relationship of equivalence point pH to total alkalinity as
described by Thomas and Lynch [153].
Willis and Mullings [152] concluded that five reagents would be sufficient to measure
alkalinity at concentrations ranging from 5 to 700mg L
−1
CaCO
3
on the Technicon
AutoAnalyzer. Solutions with concentration from 5 to 550mg L
−1
CaCO
3
will be within
the linear range of at least one reagent. The reagents used are listed in Table 2.3 along
with the range of linear and usable concentrations. The reagents that were used with the
Coulter Instrument are the same as those described in their manual and are included in
Table 2.3 for completeness. The calibration curves have a linear portion in the middle and
a curved portion on each end. The usable range includes the linear portion as well as
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