Chlorine will be found in all water as it is the
most commonly used water disinfectant in the water industry today.
Chlorine present in
water binds with bacteria leaving only a part of the original
chlorine (the free chlorine) to continue its disinfection action.
Free Chlorine reacts with ammonium ions and organic compounds to
form chlorine compounds known as combined chlorine. Combined
chlorine and free chlorine taken together are known as Total
There are a number of ways
of testing for Chlorine, but all rely on DPD standard chemistry,
which is by measuring the colour developed in a water sample
after adding a DPD reagent to the sample.
Chemical Test Kit.....(Colourimetric
The most basic method of
testing is to use a colour comparison chemical test kit, whereby the
operator compares the colour developed within the sample to a colour
chart or coloured cube.
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Disk Test Kit)....
A step up
from the chemical test kit in terms of accuracy is to use a colour
wheel comparator, which provides a better resolution and resulting
accuracy, but still depends on the operators visual interpretation
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Colorimeter or Photometer.....
The most accurate way of
measuring the colour is to use an electronic version of the
operators eye, and these are known as photometers or colorimeters.
These shine a fixed wavelength light through the sample and then the
meter measures the amount of light that has been absorbed - from
this the meter can very accurately (to 0.01mg/l) measure the
chlorine present and provide a digital readout of the result.
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An important note to remember when
deciding on a Chlorine tester is that whilst the colour changing
kits are the lower end of budget we don't all see colours in the
same way.....But the final choice would be down to a How much you
want to spend VS How accurate you want the result......