Evaluation of Septic Tank and Subsurface Wetland for

Appendix 6 - Total Dissolved Nitrogen Assay Using Potassium Persulfate Digestion
From: D’Ella, C. F.; P. A. Steudler and N. Corwin. 1977. Determination of total
nitrogen in aqueous samples using persulfate digestion. Limnol. Oceanog. 22: 760-764.
Preparation of Reagents
Oxidizer: Dissolve 3.35 g Potassium Persulfate and 3.0 g of Sodium Hydroxide in a 500
ml flask. Have approx 250 ml distilled water in the flask before adding dry reagent so the
flask does not become too hot.
Buffer: Combine 50.5 ml of 1 Molar Sodium Hydroxide and 15.45 g Boric Acid in a 500
ml flask.
0.3 N HCl: Dilute 24.8 ml concentrated HCl in a 1000 ml flask.
Fixing Samples
In an autoclavable glass vessel with tight screw top, place 20 ml of sample or standard.
Add 30 ml Oxidizer and quickly cap. NH4 converts to NH3 and this volatilizes in the
high pH. Place samples in autoclave at 100 C for 1 hour. When sample cools, add 3.0 ml
of 0.3 N HCl then cap and shake. All precipitate must be dissolved before proceeding.
When dissolved, add 4.0 ml buffer and 3.0 ml distilled water. Reagent blanks of distilled
water should be prepared as samples each day. Sample is now ready to be analyzed
according to the Nitrate Assay protocol. Remember that sample concentrations have
been diluted 1:3.
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