Hach DR2400 - Page 663

Phosphorus, Total, Digestion
Phosphorus, Total, Digestion
PhosphorusTot_PP_Other_APD_Eng_Ody.fm Page 3 of 4
Summary of Method
Phosphates present in organic and condensed inorganic forms (meta-, pyro-, or
other polyphosphates) must be converted to reactive orthophosphate before
analysis. Pretreatment of the sample with acid and heat provides the conditions
for hydrolysis of the condensed inorganic forms. Organic phosphates are
converted to orthophosphate by heating with acid and persulfate. Organically
bound phosphates are thus determined indirectly by subtracting the result of an
acid hydrolyzable phosphorus test from the total phosphorus result.
This procedure must be followed by one of the reactive phosphorus
(orthophosphate) analysis methods for determining the phosphorus content of
the sample. If the ascorbic acid (PhosVer 3) method is used to measure the
reactive phosphorus, this method is USEPA accepted for NPDES reporting.
The following reagents and apparatus are required in addition to those required
for the reactive phosphorus test.
Required Reagents
Quantity Required
Description Per Test Unit Cat. No.
Potassium Persulfate Powder Pillows...................................................1 pillow........... 100/pkg...............2451-99
Sodium Hydroxide Solution, 5.0 N........................................................2 mL ................ 100 mL MDB.......2450-32
Sulfuric Acid Solution, 5.25 N ................................................................2 mL ................ 100 mL MDB ......2449-32
Water, deionized ................................................................................................................. 4 liters ....................272-56
Required Apparatus
Cylinder, graduated, 25-mL ....................................................................1 ....................... each........................508-40
Flask, Erlenmeyer, 125-mL ......................................................................1 ....................... each........................505-43
Hot Plate, 4-inch diameter, 120 VAC......................................................1 ....................... each....................12067-01
Hot Plate, 4-inch diameter, 240 VAC......................................................1 ....................... each....................12067-02