YSI 9300 Photometer - Manual (Page 85)

PHOTOMETER TEST INSTRUCTIONS
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Ozone is used for the disinfection of swimming pool water, and in many other
water treatment systems. In swimming pool water treatment ozone is normally
introduced into the circulation system and then removed prior to the re-entry of
the water to the pool. In other water treatment systems an ozone residual may
be maintained in the water. In all cases accurate measurement of ozone
residual is essential for the control of the system or to ensure that the ozone
has been removed.
The YSI DPD Ozone method provides a simple means of measuring ozone
residuals up to a level of 2.0 mg/l. Other disinfectants such as chlorine and
bromine are frequently used in conjunction with ozone. Supplementary
procedures are therefore provided for the separate determination of these
residuals.
Method
The YSI Ozone test uses the DPD method now internationally recognised as the
standard method of testing for disinfectant residuals. In the DPD method the
reagents are provided in tablet form for maximum convenience and simplicity of
use.
Ozone reacts with diethyl-p-phenylene diamine (DPD) in buffered solution in the
presence of potassium iodide to produce a pink coloration. The intensity of the
color is proportional to the ozone concentration and is measured using a YSI
Photometer.
For the determination of ozone in the presence of chlorine or bromine, a supple-
mentary procedure using glycine is used. The glycine destroys the ozone in the
sample and the color produced in the DPD test thus corresponds to the chlorine
or bromine only. The ozone content is thus obtained by the difference between
the test readings with and without glycine.
Photometer Method
AUTOMATIC
WAVELENGTH
SELECTION
0 – 2.0 mg/l
PHOT.25.AUTO