Correcting For Dilution; Accuracy Check / User Calibration - EUTECH INSTRUMENTS WATERPROOF C401 COLORIMETER Instruction Manual

Measurement: Chlorine, Free & Total
6. Subtract the result obtained in step 5 from the result obtained in step
1 to give the true result.

2.4.4 Correcting for dilution

To correct for any reagent added to the sample to neutralise it, a dilution
correction factor must be used:
Final Volume ÷ Initial Sample Volume = Correction Factor
The final volume can be calculated by adding together the initial 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

2.4.5 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 in the range 0-
6ppm (it is advisable to check a standard at near the concentration usually
tested for using 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).
C401/301/201/102/101
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