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Nitrogen, Total
Sample Collection, Storage, and Preservation
Accuracy Check
Nitrogen, Total
Page 4 of 6
Substance
Bromide
Chloride
Hach chemists tested this chemistry on standard nitrogen solutions prepared
from the following compounds and obtained 95% recovery:
• Ammonium chloride
• Ammonium sulfate
• Ammonium acetate
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.
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.
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
Level and Effect
> 240 mg/L; positive interference
> 3000 mg/L; positive interference
• Urea
• Glycine
NitrogenTot_TNT_High_PSD_Eng_Ody.fm
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