Hach DR2400 - Page 498

Nitrogen, Total
Nitrogen, Total
Page 4 of 6
NitrogenTot_TNT_High_PSD_Eng_Ody.fm
Hach chemists tested this chemistry on standard nitrogen solutions prepared
from the following compounds and obtained 95% recovery:
Ammonium chloride or nicotinic-PTSA spikes in domestic influent, effluent and
the ASTM standard specification for substitute wastewater (D 5905-96) also
resulted in ≥ 95% recovery.
The large amounts of nitrogen-free organic compounds in some samples may
decrease digestion efficiency by consuming some of the persulfate reagent.
Samples known to contain high levels of organics should be diluted and re-run
to verify digestion efficiency.
Sample Collection, Storage, and Preservation
Collect samples in clean plastic or glass bottles. Best results are obtained with
immediate analysis.
Preserve the sample by reducing the pH to 2 or less with concentrated (at least
2 mL/L) Sulfuric Acid (Cat. No. 979-49). Store at 4 °C (39 °F) or less. Preserved
samples may be stored up to 28 days. Warm samples to room temperature and
neutralize with 5 N Sodium Hydroxide (Cat. No. 2450-26) before analysis.
Correct the test result for volume additions; see Section 3.1.3 Correcting for Volume
Additions on page 29.
Accuracy Check
This method generally yields 95–100% recovery on organic nitrogen standards.
For proof of accuracy Hach offers a set of three Primary Standards for Kjeldahl
Nitrogen (Cat. No. 22778-00).
1. Prepare one or more of the following three solutions. Each preparation is for
an equivalent 120-mg/L N standard. Use the deionized water included in
the kit or water that is free of all organic and nitrogen-containing species.
a. Weigh 1.6208 g of Ammonium p-Toluenesulfonate (PTSA). Dissolve in a
1000-mL volumetric flask with deionized water. Add deionized water to
the 1000-mL mark.
b. Weigh 2.1179 g of Glycine p-Toluenesulfonate (PTSA). Dissolve in a
1000-mL volumetric flask with deionized water. Add deionized water to
the 1000-mL mark.
c. Weigh 2.5295 g of Nicotinic p-Toluenesulfonate (PTSA). Dissolve in a
1000-mL volumetric flask with deionized water. Add deionized water to
the 1000-mL mark.
2. Analyze each of these solutions using the test procedure above. Calculate the
percent recovery for each using this formula:
Table 2 Interfering Substances
Substance Level and Effect
Bromide > 240 mg/L; positive interference
Chloride > 3000 mg/L; positive interference
• Ammonium chloride • Urea
• Ammonium sulfate • Glycine
• Ammonium acetate