LaMotte DC1600 Colorimeter - Manual (Page 77)

SILICA ~ LOW RANGE
HETEROPOLY BLUE METHOD CODE 3664
QUANTITY CONTENTS CODE
30 mL *Silica Reagent #1 *V-4466-G
30 mL *Silica Reagent #2 *V-4467-G
30 mL *Silica Reagent #3 *V-4468-G
10 g *Silica Reagent #4 *V-6284-D
1 Spoon, 0.1 g, plstaic 0699
*WARNING: Reagents marked with a * are considered hazardous substances. Material Safety Data Sheets (MSDS) are supplied for
these reagents. For your safety, read label and accompanying MSDS before using.
Silicon dioxide, SiO
2
, commonly known as silica, occurs in all natural water. Silica may be present as suspended insoluble
particles, in a colloidal or polymeric state. It may also be present in a reactive form as silicic acid or silicate ions. Silica is a
major nutrient for diatoms. A silica cycle occurs in many bodies of water containing organisms, such as diatoms, that use
silica in their skeletal structure. The silica removed from the water may be slowly returned to solution by the decomposition
of the dead organisms. The major source of silica in natural water is from the decomposition of silicate minerals in the
drainage basin from which the waters flow. Values may range from 0-75 parts per million (or mg/liter).
The presence of silica is particularly objectionable in water used for boiler feed water purposes, as it may cause the
formation of a hard, dense scale which has unusually high resistance to heat transfer. Serious loss of turbine efficiency
results from insoluble silica turbine blade deposits caused by vaporization of silica from boiler water.
APPLICATION: Drinking, surface and saline waters; domestic and industrial wastes.
RANGE: 0.0 – 4.0 ppm Silica
METHOD: Reactive silica forms a complex with ammonium molybdate in an acidic solution to produce a
yellow-green color in proportion to the amount of silica present. Phosphate also reacts with
molybdate but the addition of oxalic acid eliminates the molybdophosphoric acid complex.
This silica molybdate complex is then reduced by ascorbic acid to produce an intense blue
color.
SAMPLE HANDLING
& PRESERVATION: Silica samples may be preserved by refrigeration at 4°C in a plastic container up to one week
without any change in silica concentration.
INTERFERENCES: Sulfides and large amounts of iron interfere. Color and turbidity may be removed by
standardizing the instrument with the original water sample. Since silica is a component of
glass waste and a common contaminant, it is suggested to run a reagent blank using silica-free
water. The blank value is subtracted from the sample concentrations.
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