YSI 9300 Photometer - Manual (Page 43)

PHOTOMETER TEST INSTRUCTIONS
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Chlorine and chlorine-release compounds are widely used for the disinfection of
drinking water and swimming pools, for the control of micro-biological growth in
cooling water, and in many other water treatment systems. Accurate
measurement of the chlorine residual is an essential aspect of the control of
these chlorination processes.
The chlorine level can be expressed in terms of the free chlorine, combined
chlorine or total chlorine residuals. For the majority of applications measurement
of the free chlorine residual is the most important. The YSI DPD chlorine
method provides a simple means of measuring free, combined and total chlorine
residuals over the range 0 - 5 mg/l.
It is recommended that if any shock treatment compounds are known to have
been used in the treatment of the water to be tested, that a DPD Oxystop tablet
be included in the test procedure as outlined below.
Method
This YSI chlorine test uses the DPD method developed by Dr A T Palin and now
internationally recognised as the standard method of testing for chlorine and
other disinfectant residuals. In the YSI DPD method the reagents are provided
in tablet form for maximum convenience and simplicity of use.
Free chlorine reacts with diethyl-p-phenylene diamine (DPD) in buffered solution
to produce a pink coloration. The intensity of the color is proportional to the free
chlorine concentration. Subsequent addition of excess potassium iodide induces
a further reaction with any combined chlorine present. The color intensity is now
proportional to the total chlorine concentration; the increase in intensity repre-
sents the combined chlorine concentration. In this way it is possible to
differentiate between free and combined chlorine present in the sample. The
color intensities are measured using a YSI Photometer.
The DPD Oxystop tablet is added after measurement for free chlorine but before
the DPD No 3 tablet. It prevents the reaction between shock treatment
chemicals and potassium iodide which would give a positive response.
Photometer Method
AUTOMATIC
WAVELENGTH
SELECTION
0 – 5.0 mg/l
PHOT.7.AUTO