ASTM D8451-22

Standard Test Method for Calculation of Unfixed Chrome Concentration in Wet Blue

SIGNIFICANCE AND USE
5.1 This test method measures the amount of unfixed chrome in Wet Blue. Results may vary according to the age of the Wet Blue.
SCOPE
1.1 This test method covers the procedures to analyze and calculate unfixed chrome concentrations in Wet Blue.  
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, health, and environmental 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-2022
• ICS: 77.120.40 - Nickel, chromium and their alloys
• Technical Committee: D31 - Leather
• Drafting Committee: D31.02 - Wet Blue

Relations

• Refers: ASTM D6658-08(2020) - Standard Test Method for Volatile Matter (Moisture) of Wet Blue by Oven Drying
• Effective Date: 01-Apr-2020
• 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 D6658-08(2013) - Standard Test Method for Volatile Matter (Moisture) of Wet Blue by Oven Drying
• 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 E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• 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 D6658-08 - Standard Test Method for Volatile Matter (Moisture) of Wet Blue by Oven Drying
• Effective Date: 01-Nov-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 E177-08 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• 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 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

Overview

ASTM D8451-22: Standard Test Method for Calculation of Unfixed Chrome Concentration in Wet Blue is an internationally recognized standard developed by ASTM International. This method specifies the procedures to analyze and calculate the concentration of unfixed chrome, primarily as chromic oxide (Cr₂O₃), present in Wet Blue leather. Wet Blue refers to chrome-tanned leather that has not yet undergone further processing or finishing operations. Assessing the unfixed chrome concentration is essential for ensuring product quality, regulatory compliance, and process optimization in leather manufacturing.

The standard employs precise laboratory techniques, such as Atomic Absorption Spectrophotometry (AAS) and Inductively Coupled Plasma (ICP), to measure the amount of unfixed chrome. Results may vary depending on the age of the Wet Blue sample, and all measurements are conducted using SI units.

Key Topics

• Purpose of Testing:
  The test measures the amount of chrome not chemically bound to the leather material and removable by water extraction. This helps manufacturers validate tanning process efficiency and environmental standards.

• Sample Preparation:

  • Leather samples are cut into small sections and stored in airtight containers.
  • The moisture content of each sample is recorded, as it directly affects chrome extraction results.

• Test Procedure:

  • Soak the Wet Blue leather sample in deionized water for 20–24 hours.
  • After soaking, filter the solution and analyze the filtrate to determine unfixed chrome content.
  • Use calibrated AAS or ICP equipment for accurate quantification.

• Calculation and Reporting:
  The concentration of unfixed chrome is calculated as a percentage and in parts per million (ppm), taking into account sample weight and moisture content.

• Precision and Quality Control:
  ASTM D8451-22 includes guidelines for repeatability and reproducibility based on interlaboratory studies to ensure consistent results across different laboratories.

Applications

• Leather Industry Quality Control:
  Regular assessment of unfixed chrome in Wet Blue helps tanneries:

  • Optimize chrome tanning processes.
  • Ensure leather product compliance with regulatory requirements.
  • Maintain consistent product quality by minimizing residue chrome.

• Environmental Compliance:
  Knowing the concentration of unfixed chrome is critical for meeting environmental regulations concerning waste treatment and the potential release of chrome compounds.

• Research and Development:
  The standard test method supports R&D efforts focused on developing more efficient chrome tanning systems and alternative tanning chemistries.

• Supplier and Customer Assurance:
  Providing data on unfixed chrome content builds transparency and trust between leather suppliers and downstream manufacturers, including those in the automotive, footwear, and upholstery sectors.

Related Standards

• ASTM D6658: Test Method for Volatile Matter (Moisture) of Wet Blue by Oven Drying, which determines the moisture content of samples for accurate chrome calculations.
• ASTM D6659: Practice for Sampling and Preparation of Wet Blue and Wet White for Physical and Chemical Tests, outlining best practices for consistent sample preparation.
• ASTM E177: Practice for Use of the Terms Precision and Bias in ASTM Test Methods, referenced for statistical approach in precision analysis.
• ASTM E691: Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method, providing the framework for validation of repeatability and reproducibility.

Keywords: unfixed chrome, chromic oxide, Wet Blue leather, chrome tanning, leather quality control, ASTM D8451-22, atomic absorption spectrophotometry, ICP analysis, environmental compliance

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:D8451 −22
Standard Test Method for
Calculation of Unfixed Chrome Concentration in Wet Blue
This standard is issued under the fixed designation D8451; 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.
1. Scope 4. Summary of Test Method
1.1 This test method covers the procedures to analyze and 4.1 Thesampleissoaked,static,indeionizedwaterfor20to
calculate unfixed chrome concentrations in Wet Blue. 24 h. After 20 to 24 h of static soaking, the mixture is
thoroughly mixed, an aliquot filtered (and diluted) if necessary,
1.2 The values stated in SI units are to be regarded as
is analyzed for unfixed chrome content. Atomic Absorption
standard. No other units of measurement are included in this
Spectrophotometers using the nitrous oxide/acetylene flame or
standard.
the air/acetylene flame are acceptable to use for the analysis.
1.3 This standard does not purport to address all of the
Analysis by the ICP (Inductively Coupled Plasma) method is
safety concerns, if any, associated with its use. It is the
also acceptable.
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
5. Significance and Use
mine the applicability of regulatory limitations prior to use.
5.1 This test method measures the amount of unfixed
1.4 This international standard was developed in accor-
chrome in Wet Blue. Results may vary according to the age of
dance with internationally recognized principles on standard-
the Wet Blue.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
6. Apparatus
mendations issued by the World Trade Organization Technical
6.1 Leather Cutting Tool.
Barriers to Trade (TBT) Committee.
6.2 Styrofoam Cup, or 250 mL beaker.
2. Referenced Documents
6.3 Beaker, 250 mL capacity or equivalent.
2.1 ASTM Standards:
6.4 Beaker, 1000 mL capacity or equivalent.
D6658 Test Method for Volatile Matter (Moisture) of Wet
6.5 Volumetric Flask, 200 mL capacity or equivalent.
Blue by Oven Drying
D6659 Practice for Sampling and Preparation of Wet Blue
6.6 Volumetric Flask, 1000 mL capacity or equivalent.
and Wet White for Physical and Chemical Tests
6.7 Stirring Rod.
E177 Practice for Use of the Terms Precision and Bias in
6.8 Magnetic Stirrer.
ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to
6.9 Atomic Absorption Spectrophotometer.
Determine the Precision of a Test Method
6.10 ICP.
6.11 Scale, accurate to 0.0001 g.
3. Terminology
6.12 Filter Paper, Whatman 1 or equivalent.
3.1 Definitions:
3.1.1 unfixed chrome, n—chrome that is not chemically
6.13 Hot Plate, to be placed inside exhaust or fume hood.
bound to hide substance and may be removed by water
extraction.
7. Reagents and Materials
7.1 Purity of Reagents—Analytical Reagent (AR) Grade
shall be used in all tests. Unless otherwise indicated, it is
This test method is under the jurisdiction ofASTM Committee D31 on Leather
intended that all reagents conform to the specifications of the
and is the direct responsibility of Subcommittee D31.02 on Wet Blue.
Committee on Analytic Reagents of the American Chemical
Current edition approved April 1, 2022. Published May 2022. DOI: 10.1520/
D8451-22.
Society (ACS), where such specifications are available. Other
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
grades may be used, provided it is first ascertained that the
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
reagent is of sufficiently high purity to permit its use without
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. lessening the accuracy of determination.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8451−22
NOTE 4—Prepare the 10 ppm and 25 ppm Cr O standard solutions
7.2 Commercial Reagents—The use of commercially avail-
2 3
fresh daily (on day of use).
able pre-standardized analytical reagents and solutions is
appropriate, providing those reagents and solutions have been
7.11 Calibration and Standardization—Nitrous oxide/
prepared in accordance with and conform to the previously
acetylene flame.
mentioned specifications (see 7.1).
7.11.1 Optimize the Atomic Absorption Spectrophotometer
according to the following instrumental parameters for the
7.3 Purity of Water—Unless otherwise indicated, reference
Nitrous oxide/acetylene flame:
to water shall be understood to mean deionized water.
Wavelength 429 nm
7.4 Commercial Cr Standard, 1000 ppm.
Slit width 0.7 nm
NOTE 1—Subsections 7.5 to 7.10 only apply when nitrous oxide/
7.11.2 UsingwatertozerotheAA,createacalibrationcurve
acetylene flame is used.
with the 10 ppm and the 25 ppm Cr O standards from 7.10.11
2 3
7.5 Oxalic Acid Anhydrous, H C O [Formula weight =
2 2 4
and 7.10.12, respectively.
90.03] or oxalic acid dihydrate, H C O ·2H O [Formula
2 2 4 2
7.11.3 Obtain a reading from the AA for the 10 ppm
weight = 126.07].
commercial Cr solution. This should be 14.6 ppm (60.3 ppm)
NOTE 2—For conversion purposes,1gofthe anhydrous form is
Cr O , if the standard solution prepared in 7.10 is accurate. If
equivalent to 1.4 g of the dihydrate form. 2 3
not, the solution will need to be discarded and remade. Once
7.6 Potassium Dichromate (K Cr O )—Used in standard
2 2 7
the 1000 ppm Cr O standard solution is deemed acceptable,
2 3
Cr O solution.
2 3
retain this standard stock solution for future use. Verify 7.10
7.7 Sulfuric acid (H SO ), 95 to 98 % w/w. Used to prepare
every 6 months with commercial standard (7.9) to ensure
2 4
standard Cr O solution.
standard stock solution is still viable. If the results after six
2 3
months are not within 60.3 ppm of the commercial standard,
7.8 Sodium Bisulfite (NaHSO ).
remake your standard stock solution according to 7.10.
7.9 Using a commercially available 1000 ppm Cr standard
NOTE 5—Subsections 7.12 to 7.15 only apply when Air/Acetylene
solution (7.4), make a 10 ppm Cr solution which will be used
flame or ICP is used.
to verify the concentration of the prepared Cr O standard in
2 3
7.12 Diluted Nitric Acid—The concentration of diluted ni-
7.10. To convert from Cr to Cr O , multiply by a factor of
2 3
tric acid is specified as a ratio stating the number of the volume
1.462 [A 10 ppm Cr solution equates to a 14.62 ppm Cr O
2 3
of nitric acid to be diluted with a given number of the volume
solution].
of water. Example: Nitric acid (HNO ), 1+1 means to take one
7.10 Standard Cr O solution, (1000 ppm).
volume of concentrated nitric acid and mix with one volume of
2 3
7.10.1 Dry approximately 5.0 g potassium dichromate
water. It is the same as a 50 % dilution of the concentrated
(K Cr O ) in 100 °C overnight.
nitric acid. It doesn’t matter what the volume is, as long as the
2 2 7
7.10.2 Weight exactly 1.9356 g of oven dried K Cr O and
ratio stays the same. Warning—When preparing diluted acid
2 2 7
put in a 1000 mL beaker. solutions always add the acid to the water!
7.10.3 Add 500 mL water and stir until dissolved.
7.12.1 Nitric acid (HNO ), 1+1.
7.10.4 Carefully add 5 mL of concentrated sulfuric acid
7.13 Prepare a 100 ppm Cr standard solution by pipetting
(H SO ) while stirring.
2 4
10 mL of the 1000 ppm Cr standard solution (7.4) into a
NOTE 3—Perform in fume hood or exhaust hood, especially when volumetric flask and diluting to 100 mL with water. Invert and
adding acids.
mix well.
7.13.1 Pipet 1 mL of the 100 ppm Cr solution into a
7.10.5 Slowly add5gof sodium bisulfite (NaHSO ) while
stirring. volumetric flask. Add 5 mL 1+1 HNO and dilute to 100 mL
with water. Invert and mix well. Use this as a 1 ppm Cr
7.10.6 Place beaker with stirring rod in it on the hot plate.
standard solution.
7.10.7 Add 50 g oxalic acid anhydrous (or 70 g oxalic acid
7.13.2 Pipet 4 mL of the 100 ppm Cr solution into a
dihydrate) while stirring.
volumetric flask. Add 5 mL 1+1 HNO and dilute to 100 mL
7.10.8 Bringsolutiontoboiling(ornearboiling)for15min.
with water. Invert and mix well. Use this as a 4 ppm Cr
7.10.9 Remove from the hot plate and add 300 mL of water
standard solution.
while stirring. When cooled to room temperature, transfer
solution to a 1000 mL volumetric flask, rinsing beaker com- 7.13.3 Blank: Dilute 5 mL 1+1 HNO to 100 mL with DI
water.
pletely and into the flask with water.
NOTE 6—Prepare the 1 ppm, 4 ppm Cr standard solutions and blank
7.10.10 Bring to volume, 1000 mL, with water and mix
fresh daily (on day of use).
well. Verify Cr O content according to 7.11. Store according
2 3
to good laboratory practices.
7.14
...