ASTM D2868-10(2015)

Standard Test Method for Nitrogen Content (Kjeldahl) and Hide Substance Content of Leather, Wet Blue and Wet White

SIGNIFICANCE AND USE
4.1 The nitrogen content as determined by this test method is normally considered to be related to the amount of hide substance (protein fiber) present in the leather sample. A factor of 5.62 is normally used to calculate the hide substance from the nitrogen content.  
4.1.1 The 5.62 factor represents the average result of many analyses of animal hides, but it cannot be considered to be accurate since it varies somewhat from hide to hide of the same type, from type of hide to type of hide, and also with the thickness of hide retained in the final leather (split thickness as compared to original hide thickness). As a result of these variations, the true factor for any given leather may be expected to vary from 5.44 to 5.80 or about ±3 %.3  
4.2 A given leather sample may contain nitrogenous substances other than hide substance (protein fiber) which will be analyzed for by this test method, such as resins, dyestuffs, etc., that contain nitrogen. Therefore, although this test method is fairly accurate for determining the nitrogen content of leather, its use for determining hide substance may result in large errors.  
4.3 The hide substance value derived from this determination has a large bearing on other chemical determinations of a given leather. Any errors, such as those described in 4.1.1 and 4.2, will be carried over into these other analytical calculations.
SCOPE
1.1 This test method covers the determination of the nitrogen content of all types of leather, wet blue and wet white. The nitrogen content is used to calculate the hide substance (protein fiber) content of leather, wet blue and wet white.  
Note 1: The original test method for leather was essentially a composite of Method 6441 of Federal Test Method Standard No. 311 and Method B5 of the American Leather Chemists Association.
Note 2: Melamine, if present in bonded leather, could give an artificially high value for the calculation of protein fiber.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3 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: 30-Nov-2015
• ICS: 59.140.30 - Leather and furs
• Technical Committee: D31 - Leather
• Drafting Committee: D31.06 - Chemical Analysis

Relations

• Replaces: ASTM D2868-10 - Standard Test Method for Nitrogen Content (Kjeldahl) and Hide Substance Content of Leather
• Effective Date: 01-Dec-2015
• Replaced By: ASTM D2868-17 - Standard Test Method for Nitrogen Content (Kjeldahl) and Hide Substance Content of Leather, Wet Blue and Wet White
• Effective Date: 01-Apr-2017
• Referred By: ASTM D6016-17(2023) - Standard Test Method for Determination of Nitrogen, Water Extractable in Leather
• Effective Date: 01-Dec-2015
• Referred By: ASTM D2807-17a - Standard Test Method for Chromic Oxide in Leather (Perchloric Acid Oxidation)
• Effective Date: 01-Dec-2015
• Referred By: ASTM D6020-00(2020) - Standard Practice for Calculation of (Non-Mineral) Combined Tanning Agents and Degree of Tannage
• Effective Date: 01-Dec-2015

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D2868 − 10 (Reapproved 2015)
Standard Test Method for
Nitrogen Content (Kjeldahl) and Hide Substance Content of
Leather, Wet Blue and Wet White
This standard is issued under the fixed designation D2868; 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 3. Summary of Test Method
3.1 The specimen prepared according to an accepted proce-
1.1 This test method covers the determination of the nitro-
dure (see Note 3) is digested with acid in the presence of a
gen content of all types of leather, wet blue and wet white.The
catalyst to convert the nitrogen to ammonium ion. The ammo-
nitrogencontentisusedtocalculatethehidesubstance(protein
nium ion formed is nonvolatile under these highly acid
fiber) content of leather, wet blue and wet white.
conditions.
NOTE 1—The original test method for leather was essentially a
NOTE 3—For leather use specimen prepared per Practice D2813. For
composite of Method 6441 of Federal Test Method Standard No. 311 and
wet blue and wet white, use specimen prepared per Practice D6659.
Method B5 of the American Leather Chemists Association.
3.2 Theacidmixtureisthenmadealkalineandtheammonia
NOTE 2—Melamine, if present in bonded leather, could give an
artificially high value for the calculation of protein fiber. liberated is distilled into either a boric acid solution which
absorbs the ammonia, or a sulfuric acid solution which absorbs
1.2 The values stated in SI units are to be regarded as
the ammonia.
standard. No other units of measurement are included in this
standard.
3.3 When the boric acid solution is used, the amount of
ammonia in the boric acid is then determined by back titration
1.3 This standard does not purport to address all of the
with standardized acid using a sharp color change indicator
safety concerns, if any, associated with its use. It is the
(green to purple) to determine the end point. When the sulfuric
responsibility of the user of this standard to establish appro-
acid solution is used, the amount of ammonia in the sulfuric
priate safety and health practices and determine the applica-
acid solution is then determined by back titration with stan-
bility of regulatory limitations prior to use.
dardized base using a sharp color change indicator (purple to
green-blue) to determine the end point.
2. Referenced Documents
4. Significance and Use
2.1 ASTM Standards:
D2813 Practice for Sampling Leather for Physical and
4.1 The nitrogen content as determined by this test method
Chemical Tests
is normally considered to be related to the amount of hide
D6659 Practice for Sampling and Preparation of Wet Blue
substance (protein fiber) present in the leather sample.Afactor
for Physical and Chemical Tests
of 5.62 is normally used to calculate the hide substance from
E177 Practice for Use of the Terms Precision and Bias in
the nitrogen content.
ASTM Test Methods
4.1.1 The 5.62 factor represents the average result of many
E691 Practice for Conducting an Interlaboratory Study to
analyses of animal hides, but it cannot be considered to be
Determine the Precision of a Test Method
accuratesinceitvariessomewhatfromhidetohideofthesame
type, from type of hide to type of hide, and also with the
thickness of hide retained in the final leather (split thickness as
1 compared to original hide thickness). As a result of these
This test method is under the jurisdiction ofASTM Committee D31 on Leather
and is the direct responsibility of Subcommittee D31.06 on ChemicalAnalysis.This
variations, the true factor for any given leather may be
test method was developed in cooperation with the American Leather Chemists
expected to vary from 5.44 to 5.80 or about 63%.
Assn. (Standard Method B5 – 1954).
Current edition approved Dec. 1, 2015. Published December 2015. Originally
4.2 A given leather sample may contain nitrogenous sub-
approved in 1970. Last previous edition approved in 2010 as D2868 – 10. DOI:
stances other than hide substance (protein fiber) which will be
10.1520/D2868-10R15.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Dahl, S., “Determination of Hide Substance in the Kjeldahl Method,” in
Standards volume information, refer to the standard’s Document Summary page on Chemistry and Technology of Leather, Vol 4, Reinhold Publishing Co., New York,
the ASTM website. NY, 1965.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2868 − 10 (2015)
analyzed for by this test method, such as resins, dyestuffs, etc., 6.6 Sodium Hydroxide, Concentrated Solution (450 g/L)—
that contain nitrogen. Therefore, although this test method is Dissolve 450 g of sodium hydroxide (NaOH) pellets (98 %) in
fairly accurate for determining the nitrogen content of leather, water and dilute to 1 L.
its use for determining hide substance may result in large
6.7 Sodium Hydroxide, Standard Solution (0.1 N)—
errors.
Dissolve 10 mL of the concentrated NaOH solution (6.6)in1
4.3 The hide substance value derived from this determina- Lofboiledandcooledwater.Determinetheexactnormalityby
tion has a large bearing on other chemical determinations of a titration against the standard sulfuric acid (6.10) using the
given leather. Any errors, such as those described in 4.1.1 and mixed indicator (6.5) for the end point.
4.2,willbecarriedoverintotheseotheranalyticalcalculations.
6.8 Sucrose (C H O ).
11 22 11
5. Apparatus
6.9 Sulfuric Acid (sp gr 1.84)—Concentrated sulfuric acid
(H SO ), free from nitrogen.
2 4
5.1 Kjeldahl Apparatus consisting of:
5.1.1 Kjeldahl Flask, of 500 or 800-mL capacity for diges-
6.10 Sulfuric Acid, Standard (0.3 N)—Dissolve 9 mL of
tion of the sample.
concentratedH SO (6.9)inwateranddiluteto1L.Determine
2 4
5.1.2 Heater, (gas or electric) for the Kjeldahl flask with the exact normality by titration against an equivalent solution
fume hood or other exhaust system.
of a primary standard such as anhydrous sodium carbonate or
5.1.3 Distillation Apparatus, consisting of an efficient vapor tris (hydroxymethyl) amino methane.
trap that can be sealed tightly in the top of the Kjeldahl flask
6.11 Sulfuric Acid, Standard (0.5 N)—Available commer-
and a condenser connected to the top of the trap. All elements
cially. Determine the exact normality by titration against an
of the distillation system shall be constructed of block tin,
equivalent solution of a primary standard wuch as anhydrous
borosilicate glass, or other materials known not to react with
sodium carbonate or tris (hydroxymethyl) amino methane.
hot ammonia vapor.
6.12 Sodium Hydroxide (0.5 N)—Available commercially.
5.2 Semi-automated equipment (Kjeltec/micro-Kjeldahl)
Determine the exact normality by titration against a known
produce comparable results and may be substituted for Kjel-
solution of a primary standard such as potassium hydrogen
dahl apparatus. See Precision and Bias (12.1 – 12.4).
phthalate.
6. Reagents
7. Hazards
6.1 Purity of Reagents—Reagent grade chemicals shall be
7.1 All reagents and chemicals should be handled with care.
used in all tests. Unless otherwise indicated, it is intended that
Before using any chemical, read and follow all safety precau-
all reagents shall conform to the specifications of the Commit-
tions and instructions on the manufacturer’s label or MSDS
tee onAnalytical Reagents of theAmerican Chemical Society,
(Material Safety Data Sheet).
where such specifications are available. Other grades may be
used, provided it is first ascertained that the reagent is of
8. Standardization
sufficiently high purity to permit its use without lessening the
8.1 Blanks—Run a blank determination substituting 1.0 g of
accuracy of the determination.
sucrose in place of the leather specimen by the procedure
6.2 Purity of Water—Unless otherwise indicated, references
shown in Section 9. Calculate the blank results, as shown in
to water shall be understood to mean distilled water or water of
Section 9.5.
equal purity.
8.2 Standard—Tris (hydroxymethyl) amino methane can be
6.3 Boric Acid Indicator Solution—Dissolve 40 g of boric
usedasaninternalnitrogenstandardforthemethod.Weighout
acid (H BO ) (borax-free) in water, add 10 mL of mixed
3 3
to 0.001 g approximately1gof tris (hydroxymethyl) amino
indicator solution (6.5) and dilute to 1 L.
methaneandtransfertotheKjeldahlflask.Runthisstandardby
5,6
6.4 Catalyst Digestion Mixture —20.0gK SO + 0.6 g
2 4 the same procedure shown in Section 9. One gram of this
CuSO + 0.2 g pumice.
4 reagent is equal to 0.1156 g of N or 8.255 meq of N .
2 2
6.5 Mixed Indicator Solution —Dissolve 0.060 g of methyl
9. Procedure
red indicator and 0.040 g of methylene blue indicator in 100
mL of 95 % ethyl alcohol.
9.1 Sample and Specimen:
9.1.1 Leather—Weigh out two specimens from the prepared
sample of 0.5 6 0.05 g accurately to 0.001 g and record the
Reagent Chemicals, American Chemical Society Specifications , American
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
weight of each specimen.
listed by the American Chemical Society, see Analar Standards for Laboratory
9.1.2 Wet Blue or Wet White—Weigh out two specimens
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
from the prepared sample of 0.05 – 1.0 g accurately to 0.001 g
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
MD. and record the weight of each specimen.
Dahl, S., and Oehler, R., “The Determination of Nitrogen in Leather by the
NOTE 4—If the sample size is <0.5 g, five replicates must be analyzed.
Kjeldahl Method,” JALCA, Vol 46, 1951, pp. 317–355.
NOTE 5—The specimens for all chemical tests to be performed on the
Available as a prepared catalyst mixture from some laboratory supply
leather,wetblueorwetwhite,shouldbeweighedatthesametimetokeep
companies, for example, Alfie Packers, #20P.
Available as prepared solution from some laboratory supply companies. Hach the moisture content constant among the specimens. If only the nitrogen
Bromcresol Green Methyl Red Indicator. content is being analyzed for, then specimens for moisture analysis should
D2868 − 10 (2015)
be weighed out at the same time as those for the nitrogen analyses.
9.5 Titration (Boric acid solution)—Titrate the receiver
contents of the blank distillate immediately with the 0.3 N
9.2 Digestion—Transfer the specimen to a Kjeldahl flask,
H SO (6.10) to a purple end point (pH about 4.9). Blank
being careful that all the powder is shaken down into the main 4
determinationsruninaccordancewith8.1mayrequiretitration
bulb of the flask. Add 10 6 0.5 g of the catalyst digestion
with alkali (if they are purple at the end of the distillation). In
mixture, a few glass beads or other anti-bumping agents, and
this case, titrate with the 0.1 N NaOH solution.
25 mL of H SO . Mix the contents by gently swirling until all
2 4
of the powder is wet by the acid. Place the flask over the heater
9.6 Titration (Sulfuric acid solution)—Titrate the receiver
in the fume hood with the flask inclined at about 45°. Adjust
contents of the blank distillate immediately with the 0.5 N
the heat so that the contents boil gently (the condensate line
NaOH (6.12) to a blue-green end point. Record the volume of
shouldbewithintheneckoftheflask)andmaintainthisboiling
titrant for the blank.Titrate the receiving flasks for the samples
for 1.5 h. Cool and dilute with 250 to 300 mL of water.
to the same end-point. Record the volume of titrant for each
NOTE 6—For distillation, use either boric acid solution (9.3) or sulfuric
sample.
acid (9.4) in the receiving flasks.
10. Calculations
9.3 Distillation (Boric acid solution):
10.1 Blank (Boric acid solution)—If the blank was acid
9.3.1 Measure out 125 mL of the H BO solution with a
3 3
(purple) and required titration by the 0.1 N NaOH solution,
graduate and transfer to a 500-mL Erlenmeyer receiving flask.
then convert this value to equivalent millilitres of 0.3 N H SO
Place the receiving flask under the outlet tube from the
2 4
as follows:
condenser so that the end of the tube dips below the surface of
the H BO solution.
3 3
B 5 blank, mL of standard 5 V N /N (1)
b b a
9.3.2 Carefully pour an amount of the concentrated NaOH
where:
solution, sufficient to make the contents of the flask strongly
V = millilitres of NaOH solution required for titration of
alkaline, slowly down the side of the digestion flask so that the
b
the blank,
caustic settles to the bottom and does not mix with the acid
N = normality of the NaOH solution, and
layer. The amount of concentrated NaOH solution required is b
N = normality of the H SO .
a 2 4
about 95 mL. Connect the Kjeldahl flask to the trap immedi-
ately and be sure that the rubber stopper is tightly in place.
10.2 Nitrogen in Sample (Boric acid solution)—Calculateas
Swirl the contents gently to mix the two layers and then heat
follows for the as received basis:
sufficiently to boil the solution in the flask. Continue heating
Nitrogen, % 5 A6B 3 N 30.014 /W 3100 (2)
@~~ ! ! #
until 150 to 200 mLhas distilled over and been collected in the
where:
H BO solution in the receiver. Disconnect the flask and trap
3 3
before turning off the heat to prevent sucking the solution from
A = millilitres of H SO required for titration of the
2 4
the receiver back into the flask. Disconnect the condenser
sample,
outlet tube and rinse it off into the receiver. Dilute the contents B = millilitres of H SO required for titration of the blank
2 4
of the receiver to approximately 350 mL. (or equivalent millilitres of H SO in terms of 0.1 N
2 4
NaOH solution calculated in 10.1) (use plus B in the
9.4 Distillation (Sulfuric acid solution):
formula above if the blank was acidic and required
9.4.1 Measure out 25.0 mL of the 0.5 N H SO solution
2 4
titration by alkali. Use minus B if the blank was
from a buret into a 500-mL Erlenmeyer receiving flask. Add
alkaline and required titration by acid),
0.5 mL of the mixed indicator solution. Adjust the volume to
N = normality of the H SO , and
2 4
the 100 mLmark with DI water. Place the receving flask under
W = grams of sample.
the outlet tube from the condenser so that the end of the tube
10.3 Nitrogen in Sample (Sulfuric acid solution)—Calculate
dips below the surface of the acidic receiving solution. Prepare
as follows for the as received basis:
a receiving flask for each samp
...