Nitrogen, Total Kjeldahl
Nitrogen, Total Kjeldahl
Page 4 of 6
NitrogenTK_None_Other_NES_Eng_Ody.fm
Sample Collection, Storage, and Preservation
Collect samples in clean glass or plastic containers. Adjust the pH to 2 or less
with Sulfuric Acid (Cat. No. 979-49) (about 2 mL per liter) and cool to 4 °C
(39 °F). Preserved samples can be stored up to 28 days.
Accuracy Check
Kjeldahl Nitrogen Standard Method
This procedure checks digestion efficiency and indicates that amount of bound
nitrogen that is freed during digestion. The methods and standards available to
check digestion technique are found in the Accuracy Check section following the
procedure in the Digesdahl
®
Digestion Apparatus Instruction Manual. Using the
digested Kjeldahl standard, perform the above TKN analysis on the colorimeter.
The TKN value should come within ±3% of the value of the prepared
Kjeldahl standard.
Standard Solution Method (to check calibration accuracy only)
1. Add one drop of TKN Indicator to each 25-mL graduated mixing cylinder.
2. Fill one cylinder to the 20-mL mark with deionized water. Fill the other
cylinder to the 20-mL mark with a 1.0-mg/L NH
3
–N solution.
3. Add 3 drops of Mineral Stabilizer to each cylinder. Invert several times
to mix.
4. Add 3 drops of Polyvinyl Alcohol Dispersing agent to each cylinder.
5. Perform the TKN procedure as described in step 10 to step 16. The display
should show 26–27 mg/L TKN.
Table 1
AQUEOUS SAMPLES (Solutions of suspensions in water—less than 1% solids)
Expected Nitrogen Concentration (mg/L) Analysis Volume (mL)
0.5–28 10.0
2–112 5.0
11–560 2.00
45–2250 1.00
425–22500 0.500
DRY SAMPLES
Expected Nitrogen Concentration (mg/L) Analysis Volume (mL)
42–2200 10.0
106–5600 5.00
350–18,000 2.00
1000–56,000 1.00
4200–220,000 0.50
OILS AND FATS
Expected Nitrogen Concentration (mg/L) Analysis Volume (mL)
85–4500 10.0
210–11,000 5.00
2100–110,000 1.00
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