Hach DR2400 - Page 610

Phosphorus, Acid Hydrolyzable Digestion
Phosphorus, Acid Hydrolyzable Digestion
Page 2 of 4
PhosphorusAcidHydro_Other_AD_Eng_Ody.fm
Interferences
Sample Collection, Storage, and Preservation
Analyze the samples immediately for the most reliable results. If prompt
analysis is not possible, samples may be preserved up to 28 days by adjusting
the pH to 2 or less with Concentrated Sulfuric Acid (about 2 mL per liter)
(Cat. No. 979-49) and storing at 4 °C. Warm the sample to room temperature and
neutralize with 5.0 N Sodium Hydroxide (Cat. No. 2450-53) before analysis.
Correct for volume additions: see Section 3.1.3 Correcting for Volume Additions on
page 29.
5. Use a 1-mL calibrated
dropper to add 2.0 mL of
5.0 N Sodium Hydroxide
Solution to the flask.
Swirl to mix.
6. Pour the sample into
a 25-mL graduated
cylinder. Adjust the
volume to 25 mL with
deionized water rinsings
from the flask.
7. Proceed with a
reactive phosphorus test
of the expected acid
hydrolyzable phosphorus
concentration range.
Extend the color
development time to
10 minutes for the
Ascorbic Acid method.
Interfering
Substance
Interference Levels and Treatments
Alkaline or
highly buffered
samples
It may be necessary to add additional acid in step 3 to drop the pH of the solution below 1.
Tur bi dit y
Use 50 mL of sample and double the reagent quantities. Use 25 mL of the reacted sample to zero the
instrument in the reactive phosphorus procedure. This compensates for any color or turbidity destroyed by this
procedure.
HRS MIN SECHRS MIN SEC