Recommended method for
simultaneous digestion to measure total
nitrogen and total phosphorus in water
samples.
Source Citation
APHA, 1998. Standard
Methods for the Examination of Water and
Wastewater, 20th Edition.
American Public Health Association, Washington, D.C.
(Method 4500-N C. Persulfate Method)
Gross, A., and C. E. Boyd. 1998. A
digestion procedure for the simultaneous
determination of total nitrogen and
total phosphorus in pond water. Journal
of the World Aquaculture Society 29:
300-303.
Personal
Protective Equipment
1)
Lab coat
2)
Goggles
3)
Nitrile disposable
gloves
Reagents
Digestion Reagent
20.1 grams low
nitrogen (<0.001% N) potassium
persulfate, K2S2O8
3.0 grams sodium hydroxide pellets
Dissolve potassium
persulfate and sodium hydroxide in 800
mL ultrapure water in a 1,000 mL
volumetric flask and dilute to volume.
Store in re-pipet dispenser.
Borate Buffer Solution
61.8 grams boric acid, H3BO3
8.0 grams sodium hydroxide pellets
Dissolve boric acid and sodium
hydroxide in 800 mL ultrapure water in a
1,000 mL volumetric flask and dilute to
volume. Store in re-pipet dispenser.
6 N Sodium Hydroxide
Solution
12 grams sodium hydroxide pellets
Dissolve sodium hydroxide in 35 mL
ultrapure water in a 50 mL volumetric
flask, cool to room temperature, and
dilute to volume. Store in a brown glass
reagent bottle.
Procedure
Carry two reagent blanks and all NO3-PO4
standards through all steps of the
procedure and apply necessary
corrections to the results.
Pipet 10.0 mL of sample (unfiltered)
into a 30-mL screw-capped test (culture)
tube. Add 5.0 mL digestion reagent. Cap
tightly. Mix by inverting twice. Heat
for 30 minutes in an autoclave or
pressure cooker at 100-110 C. Slowly
cool to room temperature. Add 1.0 mL
borate buffer solution. Mix by inverting
twice. Add 3 drops of 6 N sodium
hydroxide solution. Mix by inverting
twice.
Prepare one
disposable test tube for each sample by
placing a fill mark on the disposable
test tube using the template tube. Label
each tube with a sample number. Decant
the neutralized digest into its
respective disposable test tube, filling
to the fill mark. Place these tubes in
the centrifuge ensuring the load is
balanced. Centrifuge samples for 5
minutes. Remove tubes from centrifuge
and transfer sample supernatant to
corresponding plastic
FIA tube. Place
plastic FIA tubes in the appropriate positions in the
autosampler rack. Ensure that the
neutralized NO3-PO4
standards are placed in tubes in the
autosampler standards rack. Run the
nitrate and
phosphate analyses by
FIA. This can be performed
simultaneously with a two channel system
(FIAlab-2600), or in series with a
single channel system (FIAlab-2500).
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