YSI 9300 Photometer - Manual (Page 94)

PHOTOMETER TEST INSTRUCTIONS
__________________________________________________________________________________________
Silicon, in the form of silica, is one of the earth's most abundant elements.
Silicon is found widely in natural waters as colloidal silica or soluble silicates.
Silica and silicates do not normally cause any problems in water intended for
domestic consumption. However their presence is undesirable in water used in a
variety of industrial applications. This is because of the tendency of such water
to form a hard scale on equipment. Silica and silicate containing waters are
particularly troublesome in steam generating plant such as high pressure boilers
since silica scale can build up on turbine blades.
The YSI Silica LR test provides a simple means of measuring silica and silicate levels in
natural, treated and industrial waters over the range 0 - 4 mg/l SiO
2
.
Method
Ammonium molybdate reacts with silica under acid conditions to produce
molybdosilicic acid. In the presence of a reducing agent, this compound is
reduced to form an intense blue complex. Phosphate reacts in a similar manner.
Interference by phosphate is prevented by introducing a reagent which destroys
any molybdophosphoric acid which may form.
The reagents for the method are provided in tablet form and the test is carried
out simply by adding tablets to a sample of water. The intensity of the color
produced in the test is proportional to the silica concentration and is measured
using a YSI Photometer.
Reagents and Equipment
YSI Silica No 1 Tablets
YSI Silica No 2 Tablets
YSI Silica PR Tablets
YSI 9300 or 9500 Photometer
Round Test Tubes, 10 ml glass (PT 595)
Photometer Method
AUTOMATIC
WAVELENGTH
SELECTION
0 – 4.0 mg/l SiO
2
PHOT.31.AUTO