GB
Methods
pH-value with Tablet
6.5 – 8.4
Fill a clean vial (24 mm Ø) with 10 ml of the water sample and
perform zero calibration (see “Operation").
Add one PHENOL RED PHOTOMETER tablet straight from the foil
to the 10 ml water sample and crush the tablet using a clean stirring
rod
.
Close the vial tightly with the cap and swirl gently several times until
the tablet is dissolved.
Place the vial in the sample chamber making sure that the
marks
are aligned.
Press the [ZERO/TEST] key.
The method symbol flashes for approx. 3 seconds.
The result is shown in the display as pH-value.
Tolerance: ± 0,1 pH
0.0.0
PH
Zero
Test
RESULT
Notes:
For photometric determination of pH-values only use PHENOL RED tablets in black 1.
printed foil pack and marked with PHOTOMETER.
Water samples with low values of Alkalinity-m (below 35 mg/l CaCO2.
3
) may give wrong
pH readings.
pH-values below 6.5 and above 8.4 can produce results inside the measuring range. 3.
A plausibility test (pH-meter) is recommended.
The accuracy of the colorimetric determination of pH-values depends on various 4.
boundary conditions (buffer capacity of the sample, salt contents etc.).
Salt error 5.
Correction of test results (average values) for samples with salt contents of:
Indicator Salt contents
Phenol red 1 molar
– 0.21
2 molar
– 0.26
3 molar
– 0.29
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 %
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