LaMotte SMART3 Colorimeter - Manual (Page 262)

Phosphorus in natural waters and wastewaters occurs almost exclusively in
the form of orthophosphates, condensed phosphates (pyro-, meta- and other
polyphosphates) and organically bound phosphates. Phosphates may be added in
small amounts to water supplies during treatment. Larger amounts are introduced
to water used for cleaning or laundering as components of commercial cleaning
preparations. Phosphates are used to treat boiler water and are components
of agricultural and residential fertilizers. Phosphorus is an important nutrient for
aquatic plants. The amount found in natural water is generally not more than 0.1
mg/L unless the water has become polluted from wastewater sources or excessive
drainage from agricultural areas.
APPLICATION: Drinking, surface and saline waters; domestic and
industrial waste water.
RANGE: 0.00 –3.50 mg/L Total Phosphorus as Phosphate
MDL: 0.50 mg/L
METHOD: Pretreatment of the sample with heat and acid provides
conditions for the hydrolysis of condensed inorganic
phosphates. Heat, acid and persulfate convert the
organic phosphates to orthophosphate during the
digestion. Ammonium molybdate and antimony
potassium tartrate react in a fi ltered acid medium with
dilute solutions of phosphate to form an antimony-
phosphomolybdate complex. This complex is reduced to
an intense blue colored complex by ascorbic acid. The
color is proportional to the amount of phosphate present.
SAMPLE HANDLING
& PRESERVATION:
Rinse sample bottle with 1:1 hydrochloric acid followed
by deionized water. Do not use phosphate detergents. If
the sample can not be analyzed immediately, the sample
should be preserved by adjusting the pH to 2 or less with
concentrated sulfuric acid and refrigerated at 4°C. Warm
the sample to room temperature and neutralize with 5.0
N sodium hydroxide before analyzing.
INTERFERENCES: Large amounts of turbidity may interfere. Aluminum
(200 ppm), Arsenate (any level), Chromium (100 ppm),
Copper (10 ppm), Iron (100 ppm), Nickel (300 ppm),
Silica (50 ppm), Silicate (10 ppm), Sulfi de (90 ppm) and
Zinc (80 ppm) will interfere.
PHOSPHORUS, Total, Low Range SMART3 Test Procedures 11.10
Test P
rocedures