LaMotte SMART Spectro Spectrophotometer - Manual (Page 231)

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: Boiler, cooling, and industrial water.
RANGE: 0.0–100.0 mg/L Total Phosphorus as phosphate
MDL: 5.0 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. Orthophosphate reacts in acid
conditions with ammonium vanadomolybdate to
form vanadomolybdophosphoric acid. The resulting
yellow color is proportional to the concentration of
orthophosphate.
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. Silica and
arsenate interfere only if the sample is heated. Arsenite,
fl uoride, thorium, bismuth, molybdate, thiosulfate, and
thiocyanate cause negative interference. Ferrous iron
concentrations above 100 ppm will interfere.
NOTE: For greater accuracy, use laboratory grade pipets. To order reagent refi lls,
order code R-4025.
PHOSPHORUS-TOTAL, High Range SMART Spectro Test Procedures 2.11
Test P
rocedures