Thermo Scientific AQUAfast AQ3700, User Manual

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Thermo Scientific Orion AQUAfast AQ3700 Colorimeter User Guide
1.1 Methods
Notes:
1. For photometric determination of pH values only use BROMOCRESOLPURPLE tablets
in black printed foil pack and marked with METER.
2. pH values below 5.2 and above 6.8 can produce results inside the measuring range.
A plausibility test (pH-meter) is recommended.
3. The accuracy of the colorimetric determination of pH-values depends on various
boundary conditions (buffer capacity of the sample, salt contents etc.).
4. Salt error
Correction of test results (average values) for samples with salt contents of:
Indicator Salt content
Bromcresolpurple 1 molar
– 0.26
2 molar
– 0.33
3 molar
– 0.31
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 %