Thermo Fisher Scientific C101 Colorimeter - Manual (Page 25)

Measurement: pH
C401/301/101 Colorimeter
21
2.6.1 Sample Collection
Samples may be collected in either plastic or glass bottles. It is advisable
to wash the container with sample water before the sample is collected.
For accurate results, analysis should be conducted as soon as possible
after sample collection.
2.6.2 Sample Measurement
The amount of sample used and the amount of reagent added is critical to
obtaining correct test results. Ensure that the reagent is added in a
consistent manner, with the dropper bottle being held vertically and
squeezed slowly. To increase the test accuracy, measure the 10ml
sample and reagent using calibrated pipettes. Note: 20 drops of reagent =
0.8ml.
It is important to re-calibrate the meter to each new batch of reagent used,
or if the reagent has not been used for more than a month. It is also
important to occasionally check the results obtained with a colorless pH7.0
buffer solution. If the result is outside the range pH6.9-7.1 re-calibrate the
meter (please refer to section 3.4 pH).
Due to the nature of the test method, a sample pH of less than 5.9 or
greater than 8.2 may result in false readings. Do not use this test method
to analyze samples with a pH outside of the specified range.
2.6.3 Interferences
Chlorine:
Chlorine concentrations of greater than 6ppm may interfere. To remove
this interference, add a crystal of Sodium Thiosulphate to the sample and
mix, before adding the reagent.
2.6.4 Accuracy Check / User Calibration
A colorless pH7.0 buffer (supplied) can be used to check the test accuracy
and strength of reagent.
To check the accuracy of the meter: Use a colorless pH7.0 buffer in
place of the sample water in the above test method. The result obtained
should be in the range pH6.9-7.1 (please refer to instrument’s
specifications for data on meter precision and accuracy).
To re-calibrate the meter: Please refer to section 3.4 pH for details.
pH Measuring Hints & Tips