Thermo Fisher Scientific C101 Colorimeter - Manual (Page 17)

Measurement: Chlorine, Free & Total
C401/301/201Colorimeter
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sample volume and the volume of neutralising reagent used:
Final Volume = Initial Sample Volume + Volume of Neutralising
Reagent.
The result from a test can then be multiplied by the Correction Factor
to give the true result.
If reagents are added from the supplied dropper bottles, then 25
drops is equal to 1ml.
Example:
50ml sample is neutralised using 50 drops of 1N Sulphuric Acid, and
each drop is 0.04 ml.
Initial Sample Volume = 50ml
Volume of Neutralising Reagent added = 50drops X 0.04 ml= 2ml
Final Volume = 50ml + 2ml = 52ml
Correction Factor = 52/50 = 1.04
A test result of 1.00ppm would then become 1.00ppm X 1.04 =
1.04ppm
2.4.4 Accuracy Check / User Calibration
Producing chlorine standards is a difficult procedure that should only be
attempted by trained laboratory staff. Details of preparation techniques are
not provided in this document.
The prepared chlorine standard may be used to check the accuracy of the
meter or to re-calibrate the meter. In almost all cases it is recommended
to use the default factory calibration.
To check the accuracy of the meter: Prepare a standard solution of
known concentration within the range of the instrument. It is advisable to
prepare a standard near to the concentration value usually tested with the
meter. Use this standard in place of the sample water in the above test
method. Repeat the measurement 5-7 times with different sachets and
average the results. The result obtained should be approximately the
value of the standard used (please refer to instrument’s specifications for
data on meter precision and accuracy).
To re-calibrate the meter: All instruments are factory calibrated and user
calibration is not recommended. However, if a Chlorine standard can be
prepared, measured accurately and qualified by a different method
(titration, for example) or another instrument of higher precision and
accuracy, then a Chlorine standard in the 4.1-5.0 ppm Cl
2
range can be
used. Please refer to Section 3.2 Chlorine, Free & Total, Chlorine Dioxide,