ASTM E258-07(2015)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: E258 −07 (Reapproved 2015)
Standard Test Method for
Total Nitrogen in Organic Materials by Modified Kjeldahl
Method
This standard is issued under the fixed designation E258; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* E200 Practice for Preparation, Standardization, and Storage
of Standard and Reagent Solutions for ChemicalAnalysis
1.1 This test method covers the determination of total
nitrogen in nitrogen-containing organic compounds. This test
3. Summary of Test Method
method is not applicable for use on materials containing N-O,
3.1 The sample is digested in a mixture of concentrated
N-N linkages.
sulfuric acid, potassium sulfate, and mercuric oxide. The
1.2 The values stated in SI units are to be regarded as
amounts of organic matter, potassium sulfate, and sulfuric acid
standard. The values given in parentheses are for information
present during the digestion step are critical. The organic
only.
material is oxidized and the nitrogen converted to ammonium
1.3 This standard does not purport to address all of the
sulfate. Sodium sulfide is added to the digested mixture to
safety concerns, if any, associated with its use. It is the
precipitate the mercury after which the solution is made
responsibility of the user of this standard to establish appro-
strongly alkaline with sodium hydroxide solution and the
priate safety, health, and environmental practices and deter-
ammoniawhichisliberatedisdistilledintoameasuredvolume
mine the applicability of regulatory limitations prior to use.
of standard acid. The amount of acid neutralized by the
ammonia is determined by titrating the excess acid with
NOTE 1—Another method of restricted application is given in Test
standard sodium hydroxide solution.
Method D1013.
1.4 This international standard was developed in accor-
4. Significance and Use
dance with internationally recognized principles on standard-
4.1 This test method may be used to determine the total
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom- nitrogen content of certain unknown organic samples, or to
assay known nitrogen containing organic compounds.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
4.2 This test method may be used on organic materials in
which the complete conversion of nitrogen to ammonium
2. Referenced Documents
sulfate can be accomplished by digestion in a mixture of
2.1 ASTM Standards:
sulfuric acid, potassium sulfate, and mercuric oxide. It cannot
D1013 Test Method for Determining Total Nitrogen in
be used on materials containing N–O, N–N linkages.
Resins and Plastics (Withdrawn 2007)
4.3 This test method assumes that ammonia can be quanti-
D1193 Specification for Reagent Water
tatively measured by distillation from an alkaline solution into
a measured volume of standard acid.
This test method is under the jurisdiction of ASTM Committee D16 on
5. Apparatus
Aromatic, Industrial, Specialty and Related Chemicals and is the direct responsi-
bility of Subcommittee D16.04 on Instrumental Analysis.
5.1 Kjeldahl Flasks of moderately thick, well-annealed
This test method has been adopted from Method 2.054 of the Official Methods
borosilicate glass for digestion and distillation, 500 or 800-mL
ofAnalysis of theAssociation of OfficialAgricultural Chemists, 13th Edition, 1980.
capacity.
Current edition approved June 1, 2015. Published June 2015. Originally
approved in 1965. Last previous edition approved in 2007 as E258 – 07. DOI:
5.2 Connecting Bulbs of theWillits-John type, or a scrubber
10.1520/E0258-07R15.
2 bulb equally effective in preventing mechanical carry-over of
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
the contents of the distillation flask to the condenser (Note 2).
Standards volume information, refer to the standard’s Document Summary page on
NOTE 2—The usual flask and connecting bulb commercially available
the ASTM website.
The last approved version of this historical standard is referenced on are made to be assembled by means of a rubber stopper. To minimize
www.astm.org. lacerations from broken flasks while assembling the apparatus, it is
*A Summary of Changes section appears at the end of this standard
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E258 − 07 (2015)
recommended that the flask have an outer spherical 35/25 joint and the
6.8 Sulfide Solution—Dissolve 40 g of potassium sulfide or
bulb have an inner spherical 35/25 joint. This type apparatus is held
sodium sulfide in water and dilute to 1 L.
together by a spring clamp.
6.9 Sulfuric Acid (sp gr 1.84)—Concentrated sulfuric acid
5.3 Digestion and Distillation Equipment consists of an
(H SO ).
2 4
adjustable heater, water-cooled condenser, receiver support,
and fume disposal unit. Any of the well-known commercial NOTE 4—In the analysis of samples containing nitrile or cyanate
groups, which are easily hydrolyzed, the concentrated sulfuric acid must
Kjeldahl digestion and distillation units are suitable. The units
contain essentially no water. The acid should be taken from a freshly
may be heated either electrically or by gas burner but must be
opened bottle, or boiled just prior to use, or preferably, a small amount of
adjusted after an initial warm-up period to bring 250 mL of
phosphorus pentoxide should be added to the acid.
water to a rolling boil in 4 to 6 min. Before testing the unit,
6.10 Sulfuric Acid, Standard (0.1 or 0.5 meq/mL (N))—
preheatfor10minifagasheateror30minifanelectricheater.
Prepare in accordance with the Precision and Bias Section in
For the test add three to four boiling chips to prevent super
the portion of Practice E200 pertaining to hydrochloric acid,
heating.
0.02 to 1.0 me1/mL (N). An exact standardization of this
5.4 Delivery Tubes made of moderately heavy-wall glass
reagent is not necessary.
tubing, 150 to 200 mm (6 to 8 in.) in length, for conducting the
6.11 Zinc, granular.
distillate from the condenser to the receiver.
5.5 Receiver Flask, 500-mL capacity, wide-mouth Erlen-
7. Procedure
meyer flask.
7.1 Place the sample, weighed to 0.0001 g, in a Kjeldahl
6. Reagents
digestion flask. The weight of sample will depend upon
whether 0.1 or 0.5 meq/mL (N) H SO is used as the standard
2 4
6.1 Purity of Reagents—Reagent grade chemicals shall be
acid;if0.1me1/mL (N)acidisused,thesampleshouldcontain
used in all tests. Unless otherwise indicated, it is intended that
between 14 and 56 mg of nitrogen and if 0.5 N acid is used the
all reagents shall conform to the specifications of the Commit-
sample should contain between 70 and 280 mg of nitrogen, but
tee onAnalytical Reagents of theAmerican Chemical Society,
the sample weight taken should normally be less than 2.2 g.
where such specifications are available. Other grades may be
used, provided it is first ascertained that the reagent is of
NOTE 5—The optimum weight of sample to be digested, if of unknown
sufficiently high purity to permit its use without lessening the composition,mustbedeterminedbyatrialdetermination.Sincethenature
and amount of the sample will affect the amount of acid consumed in the
accuracy of the determination.
digestion, the preferred weight of sample is one that will give the largest
6.2 Purity of Water—Unless otherwise indicated, references
amount of nitrogen within the prescribed range while using the smallest
total weight of sample and adhering to the prescribed maximum.
to water shall be understood to mean Type II or III reagent
water conforming to Specification D1193.
7.2 To the flask add 0.7 g of HgO, 15 g of K SO , and 25
2 4
mL of H SO (sp gr 1.84) (Note 3, Note 6). Place the flask in
6.3 Indicator Solution (either may be used):
2 4
an inclined position and heat gently until frothing ceases, then
6.3.1 Methyl Purple Indicator Solution—Commercially
boilbrisklycausingthecondensatetobeformedapproximately
available.
half way up the neck of the flask. Continue boiling until the
6.3.2 Methyl Red Indicator Solution—Dissolve1gof
solution clears and then for 2 h longer (Note 7).
methyl red in 200 mL of ethyl alcohol (denatured alcohol,
formula 2B, 3A, or 30A of the U.S. Bureau of Internal
NOTE 6—The temperature of the digestion mixture is critical and is
Revenue, may be used).
regulated by the ratio of salt to acid (free acid at the completion of the
digestion period). The ratio must be kept close to 1:1 (weight:volume)
6.4 Mercuric Oxide (HgO).
K SO -to-free acid in weight from the weight of acid initially added, and
2 4
6.5 Potassium Sulfate (K SO ), anhydrous (Note 3). converting weight of acid to a volume basis. If a sa
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