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PHOSPHORUS, ACID HYDROLYZABLE
SAMPLING AND STORAGE
Most reliable results are obtained when samples are analyzed
immediately. If prompt analysis is not possible, samples may be
preserved up to 24 hours by cooling to 4 °C (39 °F). Warm to room
temperature before testing.
INTERFERENCES
If the sample is turbid, use 50 mL of sample and double the reagent
volumes. Use 25 mL of the hydrolyzed sample to zero the instrument in
the reactive phosphorus procedure. This compensates for any turbidity
dissolved by this procedure.
SUMMARY OF METHOD
This procedure lists the necessary steps to convert condensed phosphate
forms (meta-, pyro- or other polyphosphates) to orthophosphate before
analysis. The procedure uses acid and heat to hydrolyze the sample.
Organic phosphates are not converted to orthophosphate by this process,
but a very small fraction may be unavoidably included in the result.
Thus, the "acid hydrolyzable" phosphate results are primarily a measure
of inorganic phosphorus. This procedure must be followed by one of the
reactive phosphorus (orthophosphate) analysis methods for
determination of the phosphorous content of the sample.
The following reagents and apparatus are required in addition to those
required for the reactive phosphorus test.
REQUIRED REAGENTS
Description
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
REQUIRED APPARATUS
Cylinder, graduated, 25 mL . . . 1 . . . . . . . . . each . . . . . . . . . . . . 508-40
Flask, erlenmeyer, 50 mL . . . . . 1 . . . . . . . . . each . . . . . . . . . . . . 505-41
Quantity
Per Test
Unit
52-105
continued
Cat. No.
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