Background Information; Introduction To Colorimetric Measurement - palintest Pooltest 25 Manual

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BACKGROUND INFORMATION

Introduction to Colorimetric Measurement

Palintest methods are based on measuring the intensity of colours produced
by Palintest reagents and using Palintest photometers to measure that
intensity of colour. This method is called colorimetry and can be defined as
any technique used to evaluate an unknown colour in reference to known
colours.
To avoid subjective measurement between test samples and colour standards,
a photometer can be used for quantitative measurement of the amount of
coloured light absorbed by a sample (with reagents added) in reference to an
untreated sample (blank).
White light is made up of many different wavelengths of visible light.
A photometer transmits a white light beam through an optical filter which
permits only one particular band of wavelength of light to pass to the
photodetector where it is measured.
The difference in the amount of coloured light transmitted by a colourless
sample (blank) and the amount of coloured light transmitted by a coloured
sample is a measurement of the amount of coloured light absorbed by the
sample.
The use of filters improves the sensitivity of this process and choice of the
correct optical filter (and therefore the correct wavelength) of light is important.
It is interesting to note that the filter that gives the most sensitive calibration
for a test factor is the complementary colour of the test sample. For example,
the chlorine test produces a pink colour proportional to the chlorine
concentration in the sample (the greater the chlorine concentration, the darker
the pink colour). In this case, a green filter gives the greatest sensitivity as a
pinkish-red solution absorbs mostly green light.
Palintest photometers calculate and then display the test results directly in
milligrams per litre (mg/l) of the test factor, by comparing the amount of
absorbed light to the calibration data programmed into the instrument.
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