YSI 9300 Photometer - Manual (Page 63)

PHOTOMETER TEST INSTRUCTIONS
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Fluoride occurs naturally in some ground waters and is often introduced into
drinking water for the prevention of tooth decay. Excessive amounts of fluoride
are however objectionable and can cause tooth discoloration.
The YSI Fluoride test provides a simple method of monitoring fluorides in
natural waters, and for the control of fluoridation plant at water works.
METHOD
Zirconyl Chloride and Eriochrome Cyanine R are reacted in acid solution to form
a red colored complex. This color is destroyed by fluoride ions to give the pale
yellow color of the Eriochrome Cyanine. Differing amounts of fluoride thus
produce a range of colors from red to yellow.
The particular advantage of this method is that it is substantially free from inter-
ferences which normally beset chemical methods of fluoride testing. In particular
interference from aluminium and iron is eliminated by making the solution alkaline
in the first stage of the test procedure. This breaks down any aluminium-fluoride
and iron-fluoride complexes which may be present in the water. Interference from
calcium, phosphates and sulphates should not be significant at the levels normally
encountered in natural and drinking waters.
In the YSI Fluoride test two tablet reagents are used. The test is simply carried
out by adding one of each tablet to a sample of the water. The color produced
in the test is indicative of the fluoride concentration and is measured using a
YSI Photometer.
REAGENTS AND EQUIPMENT
YSI Fluoride No 1 Tablets
YSI Fluoride No 2 Tablets
YSI 9300 or 9500 Photometer
Round Test Tubes, 10 ml glass (PT 595)
Photometer Method
AUTOMATIC
WAVELENGTH
SELECTION
0 – 1.5 mg/l
PHOT.14.AUTO