LaMotte SMART Spectro Spectrophotometer - Manual (Page 227)

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: 0.07 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 SMART Spectro Test Procedures 2.11
Test P
rocedures