ASTM D2868-96

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.

General Information

• Status: Historical
• Publication Date: 09-May-1996
• Technical Committee: D31 - Leather
• Drafting Committee: D31.06 - Chemical Analysis

Relations

• Replaced By: ASTM D2868-96(2001) - Standard Test Method for Nitrogen Content (Kjeldahl) and Hide Substance Content of Leather
• Effective Date: 10-May-1996
• Referred By: ASTM D6020-00(2020) - Standard Practice for Calculation of (Non-Mineral) Combined Tanning Agents and Degree of Tannage
• Effective Date: 10-May-1996
• Referred By: ASTM D6016-17(2023) - Standard Test Method for Determination of Nitrogen, Water Extractable in Leather
• Effective Date: 10-May-1996
• Referred By: ASTM D2807-17a - Standard Test Method for Chromic Oxide in Leather (Perchloric Acid Oxidation)
• Effective Date: 10-May-1996

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.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.
Designation: D 2868 – 96
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 sharp color change indicator (green to purple) to determine the
end point.
1.1 This test method covers the determination of the nitro-
gen content of all types of leather. The nitrogen content is used
4. Significance and Use
to calculate the hide substance (protein fiber) content of leather.
4.1 The nitrogen content as determined by this test method
NOTE 1—This test method is essentially a composite of Method 6441 of
is normally considered to be related to the amount of hide
Federal Test Method Standard No. 311 and Method B 5 of the American
substance (protein fiber) present in the leather sample. A factor
Leather Chemists Association.
of 5.62 is normally used to calculate the hide substance from
1.2 This standard does not purport to address all of the
the nitrogen content.
safety concerns, if any, associated with its use. It is the
4.1.1 The 5.62 factor represents the average result of many
responsibility of the user of this standard to establish appro-
analyses of animal hides, but it cannot be considered to be
priate safety and health practices and determine the applica-
accurate since it varies somewhat from hide to hide of the same
bility of regulatory limitations prior to use.
type, from type of hide to type of hide, and also with the
thickness of hide retained in the final leather (split thickness as
2. Referenced Documents
compared to original hide thickness). As a result of these
2.1 ASTM Standards:
variations, the true factor for any given leather may be
D 2813 Practice for Sampling Leather for Physical and 5
expected to vary from 5.44 to 5.80 or about 63%.
Chemical Tests
4.2 A given leather sample may contain nitrogenous sub-
E 180 Practice for Determining the Precision of ASTM
stances other than hide substance (protein fiber) which will be
Methods for Analysis and Testing of Industrial Chemicals
analyzed for by this test method, such as resins, dyestuffs, etc.,
that contain nitrogen. Therefore, although this test method is
3. Summary of Test Method
fairly accurate for determining the nitrogen content of leather,
3.1 The ground leather specimen prepared according to an
its use for determining hide substance may result in large
accepted procedure is digested with acid in the presence of a
errors.
catalyst to convert the nitrogen to ammonium ion. The ammo-
4.3 The hide substance value derived from this determina-
nium ion formed is nonvolatile under these highly acid
tion has a large bearing on other chemical determinations of a
conditions.
given leather. Any errors, such as those described in 4.1.1 and
3.2 The acid mixture is then made alkaline and the ammonia
4.2, will be carried over into these other analytical calculations.
liberated is distilled into a boric acid solution which absorbs
the ammonia. 5. Apparatus
3.3 The amount of ammonia in the boric acid is then
5.1 Kjeldahl Apparatus consisting of:
determined by back titration with standardized acid using a
5.1.1 Kjeldahl Flask, of 500 or 800-mL capacity for diges-
tion of the sample.
5.1.2 Heater, (gas or electric) for the Kjeldahl flask with
fume hood or other exhaust system.
This test method is under the jurisdiction of ASTM Committee D-31 on Leather
and is the direct responsibility of Subcommittee D31.06.01 on General Methods.
5.1.3 Distillation Apparatus, consisting of an efficient vapor
This test method was developed in cooperation with the American Leather Chemists
trap that can be sealed tightly in the top of the Kjeldahl flask
Assn. (Standard Method B 5 – 1954).
and a condenser connected to the top of the trap. All elements
Current edition approved May 10, 1996. Published July 1996. Originally
e1
of the distillation system shall be constructed of block tin,
published as D 2868 – 70 T. Last previous edition D 2868 – 73 (1991) .
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, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 2868
borosilicate glass, or other materials known not to react with to 0.001 g approximately1gof tris (hydroxymethyl) amino
hot ammonia vapor. methane and transfer to the Kjeldahl flask. Run this standard by
the same procedure shown in Section 8. One gram of this
6. Reagents
reagent is equal to 0.1156 g of N or 8.255 meq of N .
2 2
6.1 Purity of Reagents—Reagent grade chemicals shall be
8. Procedure
used in all tests. Unless otherwise indicated, it is intended that
8.1 Sample and Specimen—Weigh out two specimens from
all reagents shall conform to the specifications of the Commit-
the ground sample of 1.56 0.1 g accurately to 0.001 g and
tee on Analytical Reagents of the American Chemical Society,
record the weight of each specimen.
where such specifications are available. Other grades may be
used, provided it is first ascertained that the reagent is of
NOTE 2—The specimens for all chemical tests to be performed on the
sufficiently high purity to permit its use without lessening the leather should be weighed at the same time to keep the moisture content
constant among the specimens. If only the nitrogen content is being
accuracy of the determination.
analyzed for, then specimens for moisture analysis should be weighed out
6.2 Purity of Water—Unless otherwise indicated, references
at the same time as those for the nitrogen analyses.
to water shall be understood to mean distilled water or water of
8.2 Digestion—Transfer the specimen to a Kjeldahl flask,
equal purity.
6.3 Boric Acid Indicator Solution—Dissolve 40 g of boric being careful that all the powder is shaken down into the main
bulb of the flask. Add 10 6 0.5 g of the catalyst digestion
acid (H BO ) (borax-free) in water, add 10 mL of mixed
3 3
mixture, a few glass beads or other anti-bumping agents, and
indicator solution (5.5) and dilute to 1 L.
7,8
25 mL of H SO . Mix the contents by gently swirling until all
6.4 Catalyst Digestion Mixture — 20.0 g K SO + 0.6 g
2 4
2 4
of the powder is wet by the acid. Place the flask over the heater
CuSO + 0.2 g pumice.
in the fume hood with the flask inclined at about 45°. Adjust
6.5 Mixed Indicator Solution—Dissolve 0.060 g of methyl
the heat so that the contents boil gently (the condensate line
red indicator and 0.040 g of methylene blue indicator in 100
should be within the neck of the flask) and maintain this boiling
mL of 95 % ethyl alcohol.
for 1.5 h. Cool and dilute with 250 to 300 mL of water. Add 25
6.6 Sodium Hydroxide, Concentrated Solution (450 g/L)—
mL of Na S O solution and swirl the flask gently to mix the
Dissolve 450 g of sodium hydroxide (NaOH) pellets (9
...