ASTM D2868-96(2001)
(Test Method)Standard Test Method for Nitrogen Content (Kjeldahl) and Hide Substance Content of Leather
Standard Test Method for Nitrogen Content (Kjeldahl) and Hide Substance Content of Leather
SCOPE
1.1 This test method covers the determination of the nitrogen content of all types of leather. The nitrogen content is used to calculate the hide substance (protein fiber) content of leather.
Note 1—This test method is essentially a composite of Method 6441 of Federal Test Method Standard No. 311 and Method B 5 of the American Leather Chemists Association.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D2868–96 (Reapproved 2001)
Standard Test Method for
Nitrogen Content (Kjeldahl) and Hide Substance Content of
Leather
This standard is issued under the fixed designation D 2868; 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.
1. Scope 3.3 The amount of ammonia in the boric acid is then
determined by back titration with standardized acid using a
1.1 This test method covers the determination of the nitro-
sharp color change indicator (green to purple) to determine the
gen content of all types of leather.The nitrogen content is used
end point.
tocalculatethehidesubstance(proteinfiber)contentofleather.
NOTE 1—ThistestmethodisessentiallyacompositeofMethod 6441of 4. Significance and Use
Federal Test Method Standard No. 311 and Method B 5 of the American
4.1 The nitrogen content as determined by this test method
Leather Chemists Association.
is normally considered to be related to the amount of hide
1.2 This standard does not purport to address all of the
substance (protein fiber) present in the leather sample.Afactor
safety concerns, if any, associated with its use. It is the
of 5.62 is normally used to calculate the hide substance from
responsibility of the user of this standard to establish appro-
the nitrogen content.
priate safety and health practices and determine the applica-
4.1.1 The 5.62 factor represents the average result of many
bility of regulatory limitations prior to use.
analyses of animal hides, but it cannot be considered to be
accuratesinceitvariessomewhatfromhidetohideofthesame
2. Referenced Documents
type, from type of hide to type of hide, and also with the
2.1 ASTM Standards:
thickness of hide retained in the final leather (split thickness as
D 2813 Practice for Sampling Leather for Physical and
compared to original hide thickness). As a result of these
Chemical Tests
variations, the true factor for any given leather may be
E 180 Practice for Determining the Precision of ASTM
expected to vary from 5.44 to 5.80 or about 63%.
Methods forAnalysis and Testing of Industrial Chemicals
4.2 A given leather sample may contain nitrogenous sub-
stances other than hide substance (protein fiber) which will be
3. Summary of Test Method
analyzed for by this test method, such as resins, dyestuffs, etc.,
3.1 The ground leather specimen prepared according to an
that contain nitrogen. Therefore, although this test method is
accepted procedure is digested with acid in the presence of a
fairly accurate for determining the nitrogen content of leather,
catalyst to convert the nitrogen to ammonium ion. The ammo-
its use for determining hide substance may result in large
nium ion formed is nonvolatile under these highly acid
errors.
conditions.
4.3 The hide substance value derived from this determina-
3.2 Theacidmixtureisthenmadealkalineandtheammonia
tion has a large bearing on other chemical determinations of a
liberated is distilled into a boric acid solution which absorbs
given leather. Any errors, such as those described in 4.1.1 and
the ammonia.
4.2,willbecarriedoverintotheseotheranalyticalcalculations.
5. Apparatus
This test method is under the jurisdiction ofASTM Committee D31 on Leather
5.1 Kjeldahl Apparatus consisting of:
and is the direct responsibility of Subcommittee D31.06 on Chemical Analysis—
5.1.1 Kjeldahl Flask, of 500 or 800-mL capacity for diges-
General. This test method was developed in cooperation with theAmerican Leather
Chemists Assn. (Standard Method B 5 – 1954).
tion of the sample.
Current edition approved May 10, 1996. Published July 1996. Originally
5.1.2 Heater, (gas or electric) for the Kjeldahl flask with
e1
published as D 2868 – 70 T. Last previous edition D 2868 – 73 (1991) .
2 fume hood or other exhaust system.
Annual Book of ASTM Standards, Vol 15.04.
Annual Book of ASTM Standards, Vol 15.05.
Acceptable procedures are published in Journal of the American Leather
Chemists Association, Vol 51, 1956 p. 497; or Offıcial Methods of Analysis, Am. Dahl, S., “Determination of Hide Substance in the Kjeldahl Method,” in
Leather Chemists Assn., available through the Office of the Secretary-Treasurer, Chemistry and Technology of Leather, Vol 4, Reinhold Publishing Co., New York,
Campus Station, Cincinnati, Ohio 45221; see Practice D 2813. NY, 1965.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D2868
5.1.3 Distillation Apparatus, consisting of an efficient vapor 7. Standardization
trap that can be sealed tightly in the top of the Kjeldahl flask
7.1 Blanks—Runablankdeterminationsubstituting1.0gof
and a condenser connected to the top of the trap. All elements
sucrose in place of the leather specimen by the procedure
of the distillation system shall be constructed of block tin,
shown in Section 8. Calculate the blank results, as shown in
borosilicate glass, or other materials known not to react with
Section 9.
hot ammonia vapor.
7.2 Standard—Tris (hydroxymethyl) amino methane can be
usedasaninternalnitrogenstandardforthemethod.Weighout
6. Reagents
to 0.001 g approximately1gof tris (hydroxymethyl) amino
methaneandtransfertotheKjeldahlflask.Runthisstandardby
6.1 Purity of Reagents—Reagent grade chemicals shall be
the same procedure shown in Section 8. One gram of this
used in all tests. Unless otherwise indicated, it is intended that
reagent is equal to 0.1156 g of N or 8.255 meq of N .
2 2
all reagents shall conform to the specifications of the Commit-
tee onAnalytical Reagents of theAmerican Chemical Society,
8. Procedure
where such specifications are available. Other grades may be
8.1 Sample and Specimen—Weigh out two specimens from
used, provided it is first ascertained that the reagent is of
the ground sample of 1.56 0.1 g accurately to 0.001 g and
sufficiently high purity to permit its use without lessening the
record the weight of each specimen.
accuracy of the determination.
NOTE 2—The specimens for all chemical tests to be performed on the
6.2 Purity of Water—Unless otherwise indicated, references
leather should be weighed at the same time to keep the moisture content
to water shall be understood to mean distilled water or water of
constant among the specimens. If only the nitrogen content is being
equal purity.
analyzed for, then specimens for moisture analysis should be weighed out
6.3 Boric Acid Indicator Solution—Dissolve 40 g of boric
at the same time as those for the nitrogen analyses.
acid (H BO ) (borax-free) in water, add 10 mL of mixed
3 3
8.2 Digestion—Transfer the specimen to a Kjeldahl flask,
indicator solution (5.5) and dilute to 1 L.
being careful that all the powder is shaken down into the main
7,8
6.4 Catalyst Digestion Mixture — 20.0 g K SO + 0.6 g
2 4
bulb of the flask. Add 10 6 0.5 g of the catalyst digestion
CuSO + 0.2 g pumice.
mixture, a few glass beads or other anti-bumping agents, and
6.5 Mixed Indicator Solution—Dissolve 0.060 g of methyl
25 mL of H SO . Mix the contents by gently swirling until all
2 4
red indicator and 0.040 g of methylene blue indicator in 100
of the powder is wet by the acid. Place the flask over the heater
mL of 95 % ethyl alcohol.
in the fume hood with the flask inclined at about 45°. Adjust
the heat s
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