Cardinal Environmental Laboratories, LLC
Standard Operating Procedure
Procedure No.:3020Revision Date:17/07
Subject: (Method 351.2 )Organic Nitrogen/Total Kjeldahl Nitrogen:
Approved By:
Laboratory Director______
John PflughDate
Senior Chemist______
Roberta PettitDate
Chemist______
Zeblus HawkinsDate
TKN/Organic Nitrogen
Method EPA 351.2
Description
Organic nitrogen, found in natural compounds such as proteins, can be determined using the following methodology. The total of both organic nitrogen and ammonia concentrations is known as Total Kjeldahl Nitrogen. This method is sensitive to
0.05 ppm.
Precautions
General Requirements
Corrosives (See procedure 0020)
Sample Preservation
Samples to be analyzed for Total Kjeldahl Nitrogen (TKN) or organic nitrogen (TON)
can be collected in either plastic or glass containers. If samples cannot be analyzed immediately, preserve by adding concentrated H2SO4 to a pH of 1.5 to 2.0 and store the sample at 4°C no longer than 28 days prior to analysis.
Apparatus
- Kjeldahl flasks
- Kjeldahl distillation rack
- 250ml beakers or 250 Erlenmyer flasks
Reagents
- Copper Sulfate solution (CuS04):
Dissolve 25.1g CuSO4 in 1L water.
- TKN Acid:
Dissolve 134g K2SO4 (Potassium Sulfate) in 650ml water. Add 200ml
conc. H2SO4 slowly, dilute to 1L.
CAUTION: solution will be hot.
- TKN Base:
Dissolve 500g NaOH and 25g Na2S2O3 5H2O (Sodium Thiosulfate) in
water and dilute to 1L.
CAUTION: solution will be hot.
- See method 3010 for additional reagents.
Procedure
1.0 Determine the appropriate sample volume by the following:
SampleDI
TypeAmountH2OCuSO4TKN Acid
Aqueous samples - 100ml ---5 ml 15 ml
Waste sludge- 0.5g100 ml5 ml 15 ml
Solids- 2.0g100 ml5 ml 15 ml
1.1 A final volume for all samples should be 100ml.
2.0 Carefully add 15ml TKN acid and 5ml CuSO4 solution to the 100ml of sample
in the Kjeldahl flask.
2.1 Add 3-5 boiling chips.
2.2 Turn on the fume vacuum unit of the Kjeldahl distillation rack.
2.3 Place flask on lower rack, turn heating unit on to Hi to allow vigorous boiling. (Make sure boiling chips have been added.) Reduce volume to 20ml. As sample reduces, white fumes will be apparent.
2.4 Continue digestion on Hi for at least 30 additional minutes.
(As digestion proceeds the sample may turn clear or straw colored).
Digestion is completed when sample is reduced to 10 mls.
2.5 Turn heater mantle off and allow sample to cool completely. Do not turn the
fume vacuum unit off until sample is cooled completely.
2.6 Add 100ml ultra pure water. Carefully, (with neck pointed away), add 15ml TKN base. Swirl flask and place on top distillation rack.
2.7 Go to step 2.7 of SOP 3010 for distillation procedure. Go to step 2.1 of SOP 3010
for selection of appropriate collection scrubber.
Quality Control
*Each analytical batch analyzed for TKN must be accompanied by a method
blank consisting of 100ml ultra pure water taken through all digestion and
distillation steps.
*Each analytical batch analyzed must also be accompanied by two standards with concentrations of 2.0 ppm and 20.0 ppm
*All weights, volumes, comments etc. for each batch must be entered in
notebook form for data review.
*Every 10th sample of similar matrix shall be analyzed in duplicate and
% RPD calculated. Every 20th sample shall be analyzed as a duplicate spike
and % recoveries and % RPD calculated.
(See procedure 0110 for calculations).
*Required recoveries for duplicate and spike duplicates shall be determined using historical data. The current acceptable limits for these parameters are listed in procedure 0120.
*Failure to meet quality control acceptable limits requires corrective action.
(See procedure 0150).
References
Standard Methods for the Examination of Water and Wastewater
18th Edition - Method 4500 Norg B.
pp. 4-144 thru 4-147
Methods for Chemical Analysis of Water and Wastes
EPA 600/4-79-020 March 1983
Method 351.3 pp 351.3-1 thru 351.3-6
Procedure 3020
Revised 17/07