ASTM D3590-89(1994)e1

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
e1
Designation: D 3590 – 89 (Reapproved 1994)
Standard Test Methods for
Total Kjeldahl Nitrogen in Water
This standard is issued under the fixed designation D 3590; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Section 24, Keywords, was added in April 1994.
1. Scope * 4.2 Nitrogen compounds are widely distributed in the envi-
ronment. Sources of nitrogen include surface-applied fertiliz-
1.1 These test methods cover the determination of total
ers, cleaning products, and drinking water treatment aids.
Kjeldahl nitrogen. The following test methods are included:
Because nitrogen is a nutrient for photosynthetic organisms, it
Sections
may be important to monitor and control discharge into the
Test Method A—Manual Digestion/Distillation 8 to 14
Test Method B—Semiautomated Colorimetric Bertholt 15 to 23
environment.
1.2 The analyst should be aware that precision and bias
5. Interferences
statements included may not necessarily apply to the water
5.1 Nitrate is known to cause a serious negative interference
being tested.
in the test. Reportedly, a concentration of 250 mg/L NO
1.3 This standard does not purport to address all of the 3
results in zero recovery of mg/L N.
safety concerns, if any, associated with its use. It is the
5.2 The analyst is cautioned that ammonia in the laboratory
responsibility of the user of this standard to establish appro-
may easily become an interference in these test methods from
priate safety and health practices and determine the applica-
contamination of reagents, caps, or from the laboratory atmo-
bility of regulatory limitations prior to use.
sphere. Care should be taken that ammonium hydroxide, either
2. Referenced Documents as a reagent or as a cleaning substance, is not used in the same
room.
2.1 ASTM Standards:
D 1129 Terminology Relating to Water
6. Purity of Reagents
D 1193 Specification for Reagent Water
6.1 Reagent-grade chemicals shall be used in all tests.
D 1426 Test Methods for Ammonia Nitrogen in Water
Unless otherwise indicated, it is intended that all reagents shall
D 2777 Practice for Determination of Precision and Bias of
conform to the specifications of the Committee on Analytical
Applicable Methods of Committee D-19 on Water
Reagents of the American Chemical Society, where such
D 3370 Practices for Sampling Water from Closed Con-
specifications are available. Other grades may be used,
duits
provided it is first ascertained that the reagent is of sufficient
3. Terminology
high purity to permit its use without lessening the accuracy of
the determination.
3.1 Definitions—For definitions of terms used in these test
6.2 Purity of Water—Unless otherwise indicated, reference
methods, refer to Terminology D 1129.
to water shall be understood to mean Type III reagent water
3.2 Definitions of Terms Specific to This Standard:
conforming to Specification D 1193 for reagent water prepared
3.2.1 total Kjeldahl nitrogen—the sum of the nitrogen
by the passage through a strong, acid-cation exchange resin in
contained in the free ammonia and other nitrogen compounds
the hydrogen form.
which are converted to ammonium sulfate [(NH ) SO ] under
4 2 4
the specified digestion conditions.
7. Sampling and Preservation
4. Significance and Use 7.1 Collect the sample in accordance with applicable Prac-
tices D 3370.
4.1 These test methods are useful for measuring organic
7.2 Samples may be preserved up to 28 days by adding
nitrogen and ammoniacal nitrogen, which are essential growth
concentrated sulfuric acid to adjust to pH 2 or less and storing
nutrients.
1 3
These test methods are under the jurisdiction of ASTM Committee D-19 on Reagent Chemicals, American Chemical Society Specifications, American
Water and are the direct responsibility of Subcommittee D19.05 on Inorganic Chemical Society, Washington, DC. For suggestions on the testing of reagents not
Constituents in Water. listed by the American Chemical Society, see Analar Standards for Laboratory
Current edition approved Aug. 25, 1989. Published January 1990. Originally Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
published as D 3590 – 77. Last previous edition D 3590 – 88. and National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,
Annual Book of ASTM Standards, Vol 11.01. MD.
*A Summary of Changes section appears at the end of this standard.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 3590
at 4°C. The preserved sample should be analyzed as soon as 11.2 Ammonia Solution, Standard (1.0 mL = 0.01 mg am-
possible; data on decomposition are not available. monia nitrogen)—Dilute 10.0 mL of the stock solution (see
11.1) with water to 1 L in a volumetric flask.
TEST METHOD A—MANUAL DIGESTION/
11.3 Boric Acid Solution (2 %)—Dissolve 20 g of boric acid
DISTILLATION
(H BO ) in water and dilute to 1 L with water in a volumetric
3 3
flask.
8. Scope
11.4 Mercuric Sulfate Solution—Dissolve8gofred mer-
8.1 This test method covers the determination of total
curic oxide (HgO) in a mixture of 10 mL of sulfuric acid
Kjeldahl nitrogen in water. It measures free ammonia or
(H SO , sp gr 1.84) and 40 mL of water, and dilute solution to
2 4
ammonia formed from the conversion of nitrogen components
100 mL.
of biological origin such as amino acids and proteins. How-
11.5 Mixed Indicator Solution—Mix 2 volumes of 0.2 %
ever, the procedure may not convert the nitrogenous com-
methyl red in 95 % ethanol with 1 volume of 0.2 % methylene
pounds of some wastes to ammonia. Examples of such com-
blue in ethanol. Prepare fresh every 30 days.
pounds that may not be measured are nitro compounds,
11.6 Methyl Purple Indicator Solution (1 g/L)—Dissolve
hydrozones, oximes, nitrates, semicarbazones, pyridines, and
0.4 g of dimethyl-aminoazobenzene-o-carboxylic acid, sodium
some refractory tertiary amines.
salt, in approximately 300 mL of water. To this solution add
8.2 Three alternatives are described for the final determina-
0.55 g of a water-soluble blue dyestuff, Color Index No. 714,
tion of the ammonia: a titrimetric method, which is applicable
dissolve, and dilute to 1 L with water. This indicator is
to concentrations above 1 mg N/L; a Nesslerization method,
available commercially in a prepared form.
which is applicable to concentrations below 1 mg N/L; and a
11.7 Nessler Reagent—Dissolve 100 g of mercuric iodide
potentiometric method which is applicable to the range from
(HgI ) and 70 g of potassium iodide (KI) in a small volume of
0.04 to 1000 mg N/L.
water. Add this mixture slowly, with stirring, to a cooled
8.3 This test method is described for micro and macro
solution of 160 g of sodium hydroxide (NaOH) in 500 mL of
systems. Micro determination can be made on sample aliquots
water. Dilute the mixture to 1 L. This solution is stable for at
containing up to 10 mg of nitrogen.
least one year if stored in a thick amber polyethylene bottle out
of direct sunlight.
9. Summary of Test Method
11.8 Phenolphthalein Indicator Solution—Dissolve5gof
9.1 The sample is heated in the presence of concentrated
phenolphthalein in 500 mL of 95 % ethyl alcohol or isopro-
H SO ,K SO , and HgSO , and is digested until SO fumes
2 4 2 4 4 3
panol and add 500 mL of water. Add NaOH (0.8 g/L) solution
are obtained and the solution becomes colorless or pale yellow.
dropwise until a faint pink color appears.
The residue is cooled, diluted, and is treated and alkalized with
11.9 Sodium Hydroxide Solution (400 g/L)—Dissolve 400 g
a hydroxide-thiosulfate solution. The ammonia is distilled into
of NaOH in 800 mL of water, cool, and dilute to 1 L with water.
a boric acid solution and total Kjeldahl nitrogen is determined
11.10 Sodium Hydroxide Solution (0.8 g/L)—Dilute 2 mL
by colorimetry, titrimetry, or potentiometry.
of NaOH solution (400 g/L) (see 11.9) with water to 1 L.
11.11 Sodium Hydroxide-Sodium Thiosulfate Solution—
10. Apparatus
Dissolve 500 g of NaOH and 25 g of Na S O ·5H O in water
2 2 3 2
10.1 Digestion Apparatus—A Kjeldahl digestion apparatus
and dilute to 1 L.
with 800 to 100-mL flasks and suction takeoff to remove SO
11.12 Sulfuric Acid Solution, Standard (0.02 N, 1 mL = 0.28
fumes and water.
4 mg ammonia nitrogen)—Prepare a stock solution of approxi-
10.2 Distillation Apparatus —A macro Kjeldahl flask con-
mately 0.1 N acid by diluting 3 mL of concentrated H SO (sp
2 4
nected to a condenser and an adaptor so that the distillate can
gr 1.84) to 1 L with water. Dilute 200 mL of this solution to 1
be collected.
L with water. Standardize the approximately 0.02 N H SO
2 4
10.3 Spectrophotometer or Colorimeter, for use at 425 nm
solution against 0.0200 N Na CO solution. This last solution
2 3
with a spectral band path of not more than6 20 nm and a light
is prepared by dissolving 1.060 g of anhydrous Na CO , oven
2 3
path of 1 cm or longer.
dried at 140°C, and diluting to 1 L with water.
10.4 Electrometer (pH Meter), with expanded millivolt
11.13 Digestion Solution—Dissolve 267 g of K SO in
2 4
scale, or a specific ion meter.
5 1300 mL water and 400 mL of concentrated H SO . Add 50
2 4
10.5 Ammonia Selective Electrode.
mL of mercuric sulfate solution (see 11.4) and dilute to 2 L
10.6 Magnet Stirrer, thermally insulated.
with water. A digestion packet may be used in place of the
11. Reagents and Materials digestion solution in the macro Kjeldahl system.
11.1 Ammonia Solution Stock, (1.0 mL = 1.0 mg ammonia
nitrogen)—Dissolve 3.819 g of ammonium chloride (NH Cl)
Refers to compounds, bearing such number, as described in “Color Index,”
in water and dilute to 1 L in a volumetric flask with water.
Society of Dyers and Colourists, Yorkshire, England (1924). American Cyanamid
Company’s “Calcocid Blux AX Double” has been found satisfactory for this
purpose.
4 7
Micro Kjeldahl steam distillation apparatus is commercially available. TM Fleisher Methyl Purple indicator, U. S. Patent No. 241699, is available
EIL Model 8002-2 of Electronics Instruments Ltd. (U. S. Representative: from Fleisher Chemical Co., P. O. Box 616, Ben Franklin Station, Washington, DC
Cambridge Instrument Co., 73 Spring St., Ossining, NY 10562) has been found 20004, or from any chemical supply company handling Fleisher Methyl Purple.
satisfactory for this purpose. Also, Orion Model 95-12 has been found satisfactory Digestion packet, Kel Pak No. 5, available from the Curtin-Matheson Scientific
for this purpose. Co., has been found satisfactory for this purpose.
D 3590
12. Procedure contained in a small Erlenmeyer flask. Distill 30 mL at the rate
of 6 to 10 mL/min.
12.1 Clean the distillation apparatus with steam before use
12.3.4 Transfer to a 50-mL volumetric flask, dilute to
by distilling a 1 + 1 mixture of water and sodium hydroxide-
volume with water, and mix. Pipet 25 mL to an Erlenmeyer
thiosulfate solution (see 11.11) until the distillate is ammonia-
flask and titrate with H SO (see 12.4.1). If the concentration
free. Repeat this operation each time the apparatus is out of 2 4
is found to be below 1 mg/L determine the value colorimetri-
service long enough to accumulate ammonia (usually4hor
cally. Use 20 mL of the remaining solution for this determina-
more).
tion.
12.2 Macro Kjeldahl System:
12.4 Determination of Ammonia Distillate—Determine the
12.2.1 Place a measured sample into an 800-mL Kjeldahl
ammonia content of the distillate titrimetrically, colorimetri-
flask and dilute to 500 mL. The sample size can be determined
cally, or potentiometrically.
using the following table:
12.4.1 Titrimetric Determination—Add 3 drops of the
Kjeldahl Nitrogen in Sample,
mg/L Sample Size, mL
mixed indicator (see 11.5) to the distillate and titrate the
0to5 500
ammonia with 0.02 N H SO (see 11.12), matching the end
2 4
5to10 250
point against a blank containing the same volume of water and
10 to 20 100
20 to 50 50.0
H BO solution (see 11.3). If a pH meter is preferred, titrate to
3 3
50 to 500 25.0
pH 6.2.
Prepare a 500-mL reagent water blank.
NOTE 3—As an alternative, 2 drops of methyl purple indicator solution
12.2.2 Add 100 mL of digestion solution (see 11.13) (see
(see 11.6) may be used and the titration carried out to the intermediate
Note 1) and digest the mixture in the Kjeldahl apparatus until
gray end point.
SO fumes are given off and the solution turns colorless or pale
12.4.1.1 Calibration Curve—Prepare a series of standards
yellow. Continue heating for an additional 30 min. Cool the
on a daily basis in 50-mL volumetric flasks and dilute as
residue and add 300 mL of water. Mix well.
follows:
NOTE 1—Digesting the sample with a packet and 20 mL of concen-
Millilitres of Standard (see 11.2) 1.0 Milligrams of NH -N/50.0
trated H SO is acceptable. Cut the end of the package and empty the
2 4
mL = 0.01 mg NH -N mL
contents into the digestion flask.
0.0 0.0
0.5 0.005
12.2.3 Alkalize the digestate by careful addition of 100 mL
1.0 0.010
of sodium hydroxide-thiosulfate solution (see 11.11). Do not
2.0 0.020
mix until the digestion flask has been connected to the 4.0 0.040
5.0 0.050
distillation apparatus (see 12.2.4).
8.0 0.080
10.0 0.10
NOTE 2—Slow addition of the heavy caustic solution down the tilted
neck of the digestion flask will cause the heavier solution to underlay the
To the standards diluted to 50 mL add 1 mL of Nessler
aqueous H SO without loss of free ammonia.
2 4
reagent (see 11.7) and mix. After 20 min read the absorbance
12.2.4 Connect the Kjeldahl flask to the condenser with the
at 425 nm against the blank using 1-cm cells. From the values
tip of the condenser (or an extension of the condenser tip)
obtained for the standards plot a standard curve of absorbance
below the level of 50 mL of 2 % boric acid solution (see 11.3)
versus milligrams of NH -N.
contained in a 500-mL Erlenmeyer flask. Distill 300 mL at the
12.4.2 Colorimetric Determination (Samples)—To a 20-mL
rate of 6 to 10 mL/min.
aliquot from the macro procedure (see 12.2.5) or micro
12.2.5 Transfer the distillate to a 500-mL volumetric flask,
procedure (see 12.3.4) diluted to 50 mL, add 1 mL of Nessler
dilute to volume with water, and mix. Transfer 250 mL to an
reagent (see 11.7), and mix. After 20 min, read the absorbance
Erlenmeyer flask and titrate with H SO (see 12.4.1). If the
2 4
at 425 nm against the blank using 1-cm cells. Read the
concentration is found to be below 1 mg/L, determine the value
ammonia nitrogen in milligrams for the samples from the
colorimetrically. Use the remaining 250 mL for this
...