Lovibond CheckitDirect Mode D'emploi page 25

Methods
GB
Notes:
1. For photometric determination of pH-values only use PHENOL RED tablets in black
printed foil pack and marked with PHOTOMETER.
2. Water samples with low values of Alkalinity-m (below 35 mg/l CaCO
pH readings.
3. pH-values below 6.5 and above 8.4 can produce 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 of:
Indicator
Phenol red
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 %
CheckitDirect_Cl_Vario_pH_2b 05/2011
Salt contents
1 molar 2 molar
– 0.21 – 0.26
) may give wrong
3
3 molar
– 0.29
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