YSI 9300 Photometer - Manual (Page 41)

PHOTOMETER TEST INSTRUCTIONS
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Chlorine dioxide is used for the disinfection of water in a variety of different
applications. Chlorine dioxide is normally generated by reacting chlorine with
sodium chlorite solution in specially designed plant and equipment. Water
treated with chlorine dioxide may therefore also contain amounts of chlorine and
chlorite. For the control of such water treatment systems it is necessary to
determine and differentiate between these different residual species.
The YSI Chlorine Dioxide method provides a precise method of determining
chlorine dioxide in treated water. Supplementary procedures provide for the
determination of free and combined chlorine and chlorite.
Method
Chlorine dioxide reacts with diethyl-p-phenylene diamine (DPD) in buffered
solution to produce a pink coloration. Chlorine reacts in a similar manner. Glycine
is used to prevent the reaction with chlorine so as to give specific determination of
chlorine dioxide.
In the supplementary part of the test the glycine is omitted and it is then possible,
by differences, to measure the free chlorine content. Subsequent addition of
potassium iodide induces a further reaction with any combined chlorine present.
Continuation of the test using an acidification and neutralization procedure
produces a further reaction and in this way the chlorite concentration can be
determined.
The color intensities at each stage of the test are measured using a YSI
Photometer and the concentration of each individual component are obtained by
a simple calculation. It is normal practice to express the concentration of each
component in terms of the equivalent chlorine concentration.
Photometer Method
AUTOMATIC
WAVELENGTH
SELECTION
0 – 25.0 mg/l as Cl
0 – 9.5 mg/l as ClO
2
PHOT.7.3.AUTO