English (GB)
30
7.17 pH value, 6.5 - 8.4
7.17.1 Important notes
1. For photometric determination of pH
values, only use
Phenol red photometer
tablets in black
printed foil pack and marked with PHOTOMETER.
2. Water samples with low values of alkalinity-m* may give
wrong pH readings.
*) KS4.3 < 0.7 mmol/l ^= total alkalinity < 35 mg/l CaCO
3
3. pH values below 6.5 and above 8.4 can produce incorrect
results inside the measuring range. A plausibility test
(pH-meter) is recommended.
4. The accuracy of the colorimetric determination of pH values
depends on various boundary conditions (buffer capacity of
the sample, salt contents etc.).
5. Salt error
Correction of test results (average values) for samples with
salt contents as follows:
The values of Parson and Douglas (1926) are based on the use
of Clark and Lubs buffers.
1 mol NaCl = 58.4 g/l = 5.8 %
Indicator
Salt content of the sample
Phenol red
1 molar
2 molar
3 molar
-0.21
-0.26
-0.29
1. Fill a clean vial (
∅
24) with 10 ml of the
water sample. Close tightly with the cap.
2. Place the vial in the sample chamber
correctly. See fig.
3. Press the [Zero] key.
4. Remove the vial from the sample
chamber.
5. Add one
Phenol red photometer
tablet
(No
) straight from the foil to
the 10 ml sample and crush the tablet
using a clean stirring rod.
6. Close the vial tightly with the cap and
swirl gently several times until the tablet
is dissolved.
7. Place the vial in the sample chamber
correctly. See fig.
8. Press the [Test] key.
The result is shown in the display as pH
value.
3
3
0
prepare Zero
press ZERO
Zero accepted
prepare Test
press TEST
∅
24
Summary of Contents for DIT-M
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