ASTM D2868-17

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.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Mar-2017
• ICS: 59.140.30 - Leather and furs
• Technical Committee: D31 - Leather
• Drafting Committee: D31.06 - Chemical Analysis

Relations

• Replaces: ASTM D2868-10(2015) - Standard Test Method for Nitrogen Content (Kjeldahl) and Hide Substance Content of Leather, Wet Blue and Wet White
• Effective Date: 01-Apr-2017
• Refers: ASTM D6659-10(2015) - Standard Practice for Sampling and Preparation of Wet Blue for Physical and Chemical Tests
• Effective Date: 01-Dec-2015
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM E177-13 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2013
• Refers: ASTM E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2011
• Refers: ASTM D6659-10 - Standard Practice for Sampling and Preparation of Wet Blue for Physical and Chemical Tests
• Effective Date: 01-Oct-2010
• Refers: ASTM E177-10 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Oct-2010
• Refers: ASTM E177-08 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Oct-2008
• Refers: ASTM E691-08 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Oct-2008
• Refers: ASTM D6659-08 - Standard Practice for Sampling and Preparation of Wet Blue for Physical and Chemical Tests
• Effective Date: 01-Sep-2008
• Refers: ASTM D2813-03(2008) - Standard Practice for Sampling Leather for Physical and Chemical Tests
• Effective Date: 01-Sep-2008
• Refers: ASTM D6659-01(2007) - Standard Practice for Sampling and Preparation of Wet Blue for Physical and Chemical Tests
• Effective Date: 01-Sep-2007
• Refers: ASTM E177-06b - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 15-Nov-2006
• Refers: ASTM E177-06a - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Nov-2006

Overview

ASTM D2868-17 is the internationally recognized standard method for determining the nitrogen content (by the Kjeldahl process) and hide substance content of leather materials, specifically including leather, wet blue, and wet white. Developed by ASTM International, this method plays a crucial role in leather industry quality control and chemical analyses. The nitrogen content found through this method is directly used to estimate the protein fiber (hide substance) content in leather samples, which is essential for product specification and ensuring process consistency.

Key Topics

• Nitrogen Determination: Measures the total nitrogen content in all types of leather, wet blue, and wet white using the Kjeldahl method, following strict procedures for digestion, distillation, and titration.
• Hide Substance Calculation: Uses a standard factor (typically 5.62) to convert nitrogen content to protein fiber (hide substance), noting that this factor may vary with hide type and sample characteristics.
• Accuracy Considerations:
  • The method considers possible variation in the conversion factor due to differences among animal hides and processing variables.
  • Nitrogenous substances other than protein fiber (such as resins or finishing chemicals) can influence nitrogen measurements, potentially affecting the accuracy of hide substance estimates.
• Precision and Reproducibility: Repeatability and reproducibility values are established based on extensive round-robin testing across multiple laboratories, ensuring confidence in results under standardized conditions.
• Safety and Compliance: The standard explicitly states that users must implement appropriate safety and health practices and comply with relevant regulations.

Applications

ASTM D2868-17 serves a wide array of practical applications in the leather manufacturing and processing industry:

• Quality Control: Supports manufacturers and quality assurance teams in ensuring consistent leather quality by measuring fundamental chemical composition - especially the protein content.
• Material Verification: Enables assessment of raw, semi-processed, and finished leathers (including wet blue and wet white) for conformity with industry requirements or customer specifications.
• Chemical Process Monitoring: Provides an analytical basis for tracking changes during tanning, dyeing, or finishing processes, supporting process optimization and troubleshooting.
• Regulatory Compliance: Assists in fulfilling regulatory, safety, and labeling requirements through standardized analytical evidence.
• Research and Development: Utilized in R&D labs to compare materials, study new tanning agents, and analyze the impact of processing variables.

Related Standards

ASTM D2868-17 is commonly referenced alongside other essential standards in the leather industry, supporting its integration into broader quality systems:

• ASTM D2813: Practice for Sampling Leather for Physical and Chemical Tests
• ASTM D6659: Practice for Sampling and Preparation of Wet Blue and Wet White for Physical and Chemical Tests
• ASTM E177: Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• ASTM E691: Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

Summary

The ASTM D2868-17 Standard Test Method is vital for anyone involved in leather production, testing, or research. By providing a scientifically validated approach to determining nitrogen and hide substance contents, it ensures that leather materials meet strict quality and regulatory standards. Adhering to this method offers greater confidence in analytical results, underpins objective product comparisons, and sustains the integrity and performance of leather goods in the marketplace.

Keywords: ASTM D2868-17, leather testing, nitrogen content, Kjeldahl method, hide substance, protein fiber, wet blue, wet white, chemical analysis, leather quality control

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D2868 − 17
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.Anumber 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 and Wet White for Physical and Chemical Tests
E177Practice for Use of the Terms Precision and Bias in
1.1 This test method covers the determination of the nitro-
ASTM Test Methods
gencontentofalltypesofleather,wetblueandwetwhite.The
E691Practice for Conducting an Interlaboratory Study to
nitrogencontentisusedtocalculatethehidesubstance(protein
Determine the Precision of a Test Method
fiber) content of leather, wet blue and wet white.
NOTE 1—The original test method for leather was essentially a
3. Summary of Test Method
composite of Method6441 of Federal Test Method Standard No. 311 and
Method B5 of the American Leather Chemists Association.
3.1 The specimen prepared according to an accepted proce-
NOTE 2—Melamine, if present in bonded leather, could give an
dure (see Note 3) is digested with acid in the presence of a
artificially high value for the calculation of protein fiber.
catalyst to convert the nitrogen to ammonium ion. The ammo-
1.2 The values stated in SI units are to be regarded as
nium ion formed is nonvolatile under these highly acid
standard. No other units of measurement are included in this
conditions.
standard.
NOTE 3—For leather use specimen prepared per Practice D2813. For
1.3 This standard does not purport to address all of the
wet blue and wet white, use specimen prepared per Practice D6659.
safety concerns, if any, associated with its use. It is the
3.2 Theacidmixtureisthenmadealkalineandtheammonia
responsibility of the user of this standard to establish appro-
liberated is distilled into either a boric acid solution which
priate safety and health practices and determine the applica-
absorbstheammonia,orasulfuricacidsolutionwhichabsorbs
bility of regulatory limitations prior to use.
the ammonia.
1.4 This international standard was developed in accor-
dance with internationally recognized principles on standard-
3.3 When the boric acid solution is used, the amount of
ization established in the Decision on Principles for the
ammonia in the boric acid is then determined by back titration
Development of International Standards, Guides and Recom-
with standardized acid using a sharp color change indicator
mendations issued by the World Trade Organization Technical
(greentopurple)todeterminetheendpoint.Whenthesulfuric
Barriers to Trade (TBT) Committee.
acid solution is used, the amount of ammonia in the sulfuric
acid solution is then determined by back titration with stan-
2. Referenced Documents
dardized base using a sharp color change indicator (purple to
green-blue) to determine the end point.
2.1 ASTM Standards:
D2813Practice for Sampling Leather for Physical and
Chemical Tests 4. Significance and Use
D6659Practice for Sampling and Preparation of Wet Blue
4.1 The nitrogen content as determined by this test method
is normally considered to be related to the amount of hide
substance(proteinfiber)presentintheleathersample.Afactor
ThistestmethodisunderthejurisdictionofASTMCommitteeD31onLeather
of 5.62 is normally used to calculate the hide substance from
andisthedirectresponsibilityofSubcommitteeD31.06onChemicalAnalysis.This
test method was developed in cooperation with the American Leather Chemists
the nitrogen content.
Assn. (Standard Method B5–1954).
4.1.1 The 5.62 factor represents the average result of many
Current edition approved April 1, 2017. Published May 2017. Originally
analyses of animal hides, but it cannot be considered to be
approved in 1970. Last previous edition approved in 2015 as D2868–10 (2015).
DOI: 10.1520/D2868-17.
accuratesinceitvariessomewhatfromhidetohideofthesame
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
type, from type of hide to type of hide, and also with the
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
thicknessofhideretainedinthefinalleather(splitthicknessas
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. compared to original hide thickness). As a result of these
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2868 − 17
variations, the true factor for any given leather may be 6.5 Mixed Indicator Solution —Dissolve 0.060 g of methyl
expected to vary from 5.44 to 5.80 or about 63%. red indicator and 0.040 g of methylene blue indicator in 100
mL of 95% ethyl alcohol.
4.2 A given leather sample may contain nitrogenous sub-
stances other than hide substance (protein fiber) which will be 6.6 Sodium Hydroxide, Concentrated Solution (450 g/L)—
analyzed for by this test method, such as resins, dyestuffs, etc., Dissolve 450 g of sodium hydroxide (NaOH) pellets (98%) in
that contain nitrogen. Therefore, although this test method is water and dilute to 1 L.
fairly accurate for determining the nitrogen content of leather,
6.7 Sodium Hydroxide, Standard Solution (0.1 N)—
its use for determining hide substance may result in large
Dissolve 10 mL of the concentrated NaOH solution (6.6)in1
errors.
Lofboiledandcooledwater.Determinetheexactnormalityby
4.3 The hide substance value derived from this determina- titration against the standard sulfuric acid (6.10) using the
tion has a large bearing on other chemical determinations of a mixed indicator (6.5) for the end point.
given leather.Any errors, such as those described in 4.1.1 and
6.8 Sucrose (C H O ).
11 22 11
4.2,willbecarriedoverintotheseotheranalyticalcalculations.
6.9 Sulfuric Acid (sp gr 1.84)—Concentrated sulfuric acid
5. Apparatus
(H SO ), free from nitrogen.
2 4
5.1 Kjeldahl Apparatus consisting of:
6.10 Sulfuric Acid, Standard (0.3 N)—Dissolve 9 mL of
5.1.1 Kjeldahl Flask, of 500 or 800-mL capacity for diges-
concentratedH SO (6.9)inwateranddiluteto1L.Determine
2 4
tion of the sample.
the exact normality by titration against an equivalent solution
5.1.2 Heater, (gas or electric) for the Kjeldahl flask with
of a primary standard such as anhydrous sodium carbonate or
fume hood or other exhaust system.
tris (hydroxymethyl) amino methane.
5.1.3 Distillation Apparatus,consistingofanefficientvapor
6.11 Sulfuric Acid, Standard (0.5 N)—Available commer-
trap that can be sealed tightly in the top of the Kjeldahl flask
cially. Determine the exact normality by titration against an
and a condenser connected to the top of the trap.All elements
equivalent solution of a primary standard such as anhydrous
of the distillation system shall be constructed of block tin,
sodium carbonate or tris (hydroxymethyl) amino methane.
borosilicate glass, or other materials known not to react with
6.12 Sodium Hydroxide (0.5 N)—Available commercially.
hot ammonia vapor.
Determine the exact normality by titration against a known
5.2 Semi-automated equipment (Kjeltec/micro-Kjeldahl)
solution of a primary standard such as potassium hydrogen
produce comparable results and may be substituted for Kjel-
phthalate.
dahl apparatus. See Precision and Bias (12.1 – 12.4).
6.13 When using semi-automatic equipment, follow the
6. Reagents
guidelines provided by the manufacturer.
6.1 Purity of Reagents—Reagent grade chemicals shall be
7. Hazards
used in all tests. Unless otherwise indicated, it is intended that
7.1 Allreagentsandchemicalsshouldbehandledwithcare.
all reagents shall conform to the specifications of the Commit-
Before using any chemical, read and follow all safety precau-
tee onAnalytical Reagents of theAmerican Chemical Society,
tions and instructions on the manufacturer’s label or SDS
where such specifications are available. Other grades may be
(Safety Data Sheet).
used, provided it is first ascertained that the reagent is of
sufficiently high purity to permit its use without lessening the
8. Standardization
accuracy of the determination.
8.1 Blanks—Runablankdeterminationsubstituting1.0gof
6.2 Purity of Water—Unless otherwise indicated, references
sucrose in place of the leather specimen by the procedure
to water shall be understood to mean distilled water, deionized
shown in Section 9. Calculate the blank results, as shown in
water, or water of equal purity.
Section 9.3.
6.3 Boric Acid Indicator Solution—Dissolve 40 g of boric
8.2 Standard—Tris (hydroxymethyl) amino methane can be
acid (H BO ) (borax-free) in water, add 10 mL of mixed
3 3
usedasaninternalnitrogenstandardforthemethod.Weighout
indicator solution (6.5) and dilute to 1 L.
to 0.001 g approximately1gof tris (hydroxymethyl) amino
5,6
6.4 Catalyst Digestion Mixture —20.0gK SO +0.6 g
2 4
methaneandtransfertotheKjeldahlflask.Runthisstandardby
CuSO +0.2 g pumice.
4 the same procedure shown in Section 9. One gram of this
reagent is equal to 0.1156 g of N or 8.255 meq of N .
2 2
Dahl, S., “Determination of Hide Substance in the Kjeldahl Method,” in
Chemistry and Technology of Leather, Vol 4, Reinhold Publishing Co., New York,
9. Procedure
NY, 1965.
4 9.1 Procedure A – Kjeldahl Apparatus
Reagent Chemicals, American Chemical Society Specifications , American
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
9.1.1 Sample and Specimen:
listed by the American Chemical Society, see Analar Standards for Laboratory
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, Available as a prepared catalyst mixture from some laboratory supply
MD. companies, for example, Alfie Packers, #20P.
5 7
Dahl, S., and Oehler, R., “The Determination of Nitrogen in Leather by the Available as prepared solution from some laboratory supply companies. Hach
Kjeldahl Method,” JALCA, Vol 46, 1951, pp. 317–355. Bromcresol Green Methyl Red Indicator.
D2868 − 17
9.1.1.1 Leather—Weigh out two specimens from the pre- about 95 mL. Connect the Kjeldahl flask to the trap immedi-
pared sample of 0.5 6 0.05 g accurately to 0.001 g and record ately and be sure that the rubber stopper is tightly in place.
the weight of each specimen. Swirl the contents gently to mix the two layers and then heat
9.1.1.2 Wet Blue or Wet White—Weigh out two specimens sufficiently to boil the solution in the flask. Continue heating
until150to200mLhasdistilledoverandbeencollectedinthe
from the prepared sample of 0.5 – 1.0 g accurately to 0.001 g
and record the weight of each specimen. solution in the receiver. Disconnect the flask and trap before
turning off the heat to prevent sucking the solution from the
NOTE 4—The specimens for all chemical tests to be performed on the
receiver back into the flask. Disconnect the condenser outlet
leather,wetblueorwetwhite,shouldbeweighedatthesametimetokeep
tubeandrinseitoffintothereceiver.Dilutethecontentsofthe
the moisture content constant among the specimens. If only the nitrogen
contentisbeinganalyzedfor,thenspecimensformoistureanalysisshould
receiver to approximately 350 mL.
be weighed out at the same time as those for the nitrogen analyses.
9.1.5 Titration (Boric acid solution)—Titrate the receiver
9.1.2 Digestion—Transfer the specimen to a Kjeldahl flask, contents of the blank distillate immediately with the 0.3 N
HSO (6.10) to a purple end point (pH about 4.9). Blank
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 determinationsruninaccordancewith8.1mayrequiretitration
with alkali (if they are purple at the end of the distillation). In
mixture, a few glass beads or other anti-bu
...