EPA351.2

INSTRUMENTATION:STORET No.1.0

Scope and Application1.1

Pending Approval for NPDES (Issued 1978)Nitrogen, Kjeldahl, Total (Colorimetric,Semi-Automated Digester, AAII)CAS # N Nitrogen 7727-37-9Autoanalyzer00625

This method covers the determination of total Kjeldahl nitrogen in drinkingand surface waters, domestic and industrial wastes. The procedure convertsnitrogen components of biological origin such as amino acids, proteins andpeptides to ammonia, but may not convert the nitrogeneous compounds ofsome industrial wastes such as amines, nitro compounds, hydrazones, oximes,semicarbazones and some refractory tertiary amines. The applicable range ofthis method is 0.1 to 20 mg/L TKN. The range may be extended with sampledilution.

2.0Summary of Method2.1

The sample is heated in the presence of sulfuric acid, K2SO4and HgSO4 for twoand one half hours. The residue is cooled, diluted to 25 mL and placed on theAutoAnalyzer for ammonia determination. This digested sample may also beused for phosphorus determination.

3.0Definitions3.13.2

Total Kjeldahl nitrogen is defined as the sum of free-ammonia and organicnitrogen compounds which are converted to ammonium sulfate (NH4)2SO4,under the conditions of digestion described below.

Organic Kjeldahl nitrogen is defined as the difference obtained by subtractingthe free-ammonia value (Method 350.2, Nitrogen, Ammonia, this manual) fromthe total Kjeldahl nitrogen value.

4.0Sample Handling and Preservation4.1

Samples may be preserved by addition of 2 mL of conc H2SO4 per liter andstored at 4°C. Even when preserved in this manner, conversion of organicnitrogen to ammonia may occur. Therefore, samples should be analyzed assoon as possible.

5.0Apparatus5.1

Block Digester-40

5.25.3

6.0

Technicon Manifold for Ammonia (Figure 1)

Chemware TFE (Teflon boiling stones), Markson Science, Inc., Box 767, Delmar,CA 92014)

Reagents6.16.26.36.46.56.66.7

Mercuric Sulfate: Dissolve 8 g red mercuric oxide (HgO) in 50 mL of 1:4

sulfuric acid (10 mL conc H2SO4: 40 mL distilled water) and dilute to 100 mLwith distilled water.

Digestion Solution: (Sulfuric acid-mercuric sulfate potassium sulfate solution):Dissolve 133 g of K2SO4in 700 mL of distilled water and 200 mL of conc H2SO4.Add 25 mL of mercuric sulfate solution and dilute to 1 liter.

Sulfuric Acid Solution (4%): Add 40 mL of conc. sulfuric acid to 800 mL ofammonia free distilled water, cool and dilute to 1 liter.

Stock Sodium Hydroxide (20%): Dissolve 200 g of sodium hydroxide in 900 mLof ammonia-free distilled water and dilute to 1 liter.

Stock Sodium Potassium Tartrate Solution (20%): Dissolve 200 g sodium

potassium -tartrate in about 800 mL of ammonia-free distilled water and diluteto 1 liter.

Stock Buffer Solution: Dissolve 134.0 g of sodium phosphate, dibasic(Na2HPO4) in about 800 mL of ammonia free water. Add 20 g of sodiumhydroxide and dilute to 1 liter.

Working Buffer Solution: Combine the reagents in the stated order; add 250mL of stock sodium potassium tartrate solution (6.5) to 200 mL of stock buffersolution (6.6) and mix. Add xx mL sodium hydroxide solution (6.4) and diluteto 1 liter. See concentration ranges, Table I, for composition of working buffer. Sodium Salicylate/Sodium Nitroprusside Solution: Dissolve 150 g of sodiumsalicylate and 0.3 g of sodium nitroprusside in about 600 mL of ammonia freewater and dilute to 1 liter.

Sodium Hypochlorite Solution: Dilute 6.0 mL sodium hypochlorite solution(clorox) to 100 mL with ammonia free distilled water.

Ammonium chloride, stock solution: Dissolve 3.819 g NH4Cl in distilled waterand bring to volume in a 1 liter volumetric flask. 1 ml= 1.0 mg NH3-N.

6.86.96.10

7.0

Procedure

Digestion7.1To 20 or 25 mL of sample, add 5 mL of digestion solution (6.2) and mix (use a

vortex mixer).

7.2Add (4-8) Teflon boiling stones (5.3). Too many boiling chips will cause the

sample to boil over.

7.3With Block Digester in manual mode set low and high temperature at 160°C

and preheat unit to 160°C. Place tubes in digester and switch to automatic

mode. Set low temperature - timer for 1 hour. Reset high temperature to 380°Cand set timer for 2 1/2 hours.

7.4Cool sample and dilute to 25 mL with ammonia free water.

Colorimetric Analysis7.57.67.77.8

Check the level of all reagent containers to ensure an adequate supply.Excluding the salicylate line, place all reagent lines in their respectivecontainers, connect the sample probe to the Sampler IV and start theproportioning pump.

Flush the Sampler IV wash receptacle with about 25 mL of 4.0% sulfuric acid(6.3).

When reagents have been pumping for at least five minutes, place the

salicylate line in its respective container and allow the system to equilibrate. Ifa precipitate forms after the addition of salicylate, the pH is too low.

Immediately stop the proportioning pump and flush the coils with water usinga syringe. Before restarting the system, check the concentration of the sulfuricacid solutions and/or the working buffer solution.

To prevent precipitation of sodium salicylate in the waste tray, which can clogthe tray outlet, keep the nitrogen flowcell pump tube and the nitrogen

Colorimeter \"To Waste\" tube separate from all other lines or keep tap waterflowing in the waste tray.

After a stable baseline has been obtained start the Sampler.

7.9

7.10

8.0

Calculations8.1

Prepare standard curve by plotting peak heights of processed standardsagainst concentration values. Compute concentrations by comparing samplepeak heights with standard curve.

9.0Precision and Accuracy9.19.2

In a single laboratory (EMSL), using sewage samples of concentrations of 1.2,2.6, and 1.7 mg N/L, the precision was +/- 0.07, +/- 0.03 and +/-0.15,respectively.

In a single laboratory (EMSL), using sewage samples of concentrations of 4.7and 8.74 mg N/L, the recoveries were 99 and 99%, respectively.

Bibliography

1.2.3.4.5.

McDaniel, W.H., Hemphill, R.N. and Donaldson, W.T., \"Automatic Determination ofTotal Kjeldahl Nitrogen in Estuarine Water\1967.

Gales, M.E., and Booth, R.L., \"Evaluation of Organic Nitrogen Methods\of Research and Monitoring, June, 1972.

Gales, M.E. and Booth, R.L., \"Simultaneous and Automated Determination of TotalPhosphorus and Total Kjeldahl Nitrogen\Assurance Research Laboratory, May, 1974.

Technicon \"Total Kjeldahl Nitrogen and Total Phosphorus BD-40 Digestion Procedurefor Water\

Gales, M.E., and Booth, R.L., \"Evaluation of the Block Digestion System for the

Measurement of Total Kjeldahl Nitrogen and Total Phosphorus\Environmental Monitoring and Support Laboratory, Cinncinnati, Ohio.

TABLE 1. CONCENTRATION RANGES (NITROGEN)

Dilution loops Initial sample ResampleSample lineDiluent lineResample lineDiluent line.80 (RED/RED).80 (RED/RED).32 (BLK/BLK).80 (RED/RED).80 (RED/RED).80 (RED/RED).32 (BLK/BLK).80 (RED/RED).16 (ORN/YEL).80 (RED/RED).32 (BLK/BLK).16 (ORN/YEL).80 (RED/RED).32 (BLK/BLK).16 (ORN/YEL).80 (RED/RED).32 (ORN/YEL).16 (ORN/YEL).80 (RED/RED).32 (ORN/YEL)

.80 (RED/RED).80 (RED/RED).80 (RED/RED).80 (RED/RED)

Approx. std.cal. setting700100700100700100

RangePPM N(±10%)0-0.50-1.50-10-50-20-10

ml stock NaOHper liter workingbuffer solution2502501201208080

No. 1 2 3 4 5 6