ASTM D7638-10(2021)

Standard Test Method for Determination of Fatty Acids and Esters in Glycerin

SIGNIFICANCE AND USE
4.1 Any residual fatty acid and esters (FA&E) should be present only at very low levels in purified glycerine.  
4.2 This procedure requires the addition of a measured volume of sodium hydroxide, in excess of the amount actually needed to react with FA&E in the glycerine sample. After boiling, the excess sodium hydroxide is back titrated with standardized hydrochloric acid. The quantity of the substance being titrated is calculated as the difference between the volumes of the sodium hydroxide solution originally added, corrected by means of a blank titration, and that was consumed by the titrant in the back titration.
Note 1: The standardized solutions for sodium hydroxide and hydrochloric acid are commercially available.
SCOPE
1.1 This test method provides the quantitative determination of the fatty acid and ester content in purified glycerin by the titrimetric method.  
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 may involve hazardous materials, operations and equipment. 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. Specific precautions are listed in Section 8.  
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-Aug-2021
• ICS: 71.080.60 - Alcohols. Ethers
• Technical Committee: D15 - Engine Coolants and Related Fluids
• Drafting Committee: D15.04 - Chemical Properties

Relations

• Refers: ASTM D4725-13 - Standard Terminology for Engine Coolants and Related Fluids
• Effective Date: 01-Oct-2013
• Refers: ASTM D4725-11 - Standard Terminology for Engine Coolants
• Effective Date: 01-Jun-2011
• Refers: ASTM D4725-08a - Standard Terminology for Engine Coolants
• Effective Date: 01-Jun-2008
• Refers: ASTM D4725-08 - Standard Terminology for Engine Coolants
• Effective Date: 15-May-2008
• Refers: ASTM D4725-06 - Standard Terminology for Engine Coolants
• Effective Date: 01-Jun-2006
• Refers: ASTM D1193-06 - Standard Specification for Reagent Water
• Effective Date: 01-Mar-2006
• Refers: ASTM D4725-04 - Standard Terminology for Engine Coolants
• Effective Date: 01-May-2004
• Refers: ASTM D1193-99e1 - Standard Specification for Reagent Water
• Effective Date: 10-Feb-1999
• Refers: ASTM D1193-99 - Standard Specification for Reagent Water
• Effective Date: 10-Feb-1999
• Refers: ASTM D4725-98 - Standard Terminology for Engine Coolants
• Effective Date: 10-Jun-1998

Overview

ASTM D7638-10(2021), Standard Test Method for Determination of Fatty Acids and Esters in Glycerin, establishes a reliable, titrimetric procedure for quantifying the content of residual fatty acids and esters (FA&E) in purified glycerin. Developed by ASTM International, this standard provides users with a consistent approach to quality control, ensuring that glycerin used in various industrial applications meets strict purity requirements. This method is widely respected for its precision and for meeting the criteria defined by international guidelines and trade agreements.

Key Topics

• Quantitative Determination: The test method delivers an accurate measurement of fatty acids and esters in glycerin. It involves titration using sodium hydroxide and hydrochloric acid, with results calculated based on the difference in titrant volumes.
• Purity of Chemicals and Equipment: Only high-purity reagents and SI units are specified. All glassware and equipment should meet rigorous calibration standards to avoid contamination and ensure accuracy.
• Safety and Compliance: The standard highlights the importance of health, safety, and environmental practices. Users must address potential hazards associated with chemicals like sodium hydroxide and hydrochloric acid, and review Safety Data Sheets and laboratory best practices before use.
• Precision and Repeatability: The standard provides data regarding the repeatability and reproducibility of the test, supporting quality assurance and laboratory accreditation processes.

Applications

ASTM D7638-10(2021) is essential for industries where glycerin is a critical ingredient, particularly:

• Pharmaceuticals: Ensures that glycerin used in drug formulations contains minimal impurities, reducing risks related to product efficacy and safety.
• Cosmetics and Personal Care: Supports manufacturers in complying with stringent purity standards for ingredients in lotions, creams, and soaps.
• Food Industry: Assures food-grade glycerin contains negligible fatty acids and esters, maintaining the taste, safety, and stability of consumable products.
• Chemical Processing: Used in quality control laboratories where glycerin serves as a base or intermediate in chemical syntheses and formulations.
• Engine Coolants and Antifreeze: As referenced in related engine coolant standards, the test method helps monitor the purity of glycerin-based fluids.

By accurately measuring and limiting FA&E in glycerin, companies can guarantee safer, higher-quality products and maintain regulatory compliance across international markets.

Related Standards

• ASTM D1193: Specification for Reagent Water, providing guidance on the types of water required in laboratory testing.
• ASTM D4725: Terminology for Engine Coolants and Related Fluids, ensuring common understanding within the industry.
• USP 31 Glycerin Monograph: Outlines testing parameters for pharmaceutical-grade glycerin.
• ISO Methods: While not directly referenced, ISO standards on chemical purity and titration may be relevant for facilities operating in multidisciplinary environments or exporting products globally.

Conclusion

ASTM D7638-10(2021) is a key standard for the determination of fatty acids and esters in glycerin, supporting the production of high-purity glycerin for pharmaceuticals, cosmetics, food, and chemical industries. By providing a precise and standardized analytical method, this ASTM standard ensures the safety, quality, and compliance of glycerin-based products for global trade and consumer use. Always refer to related standards and maintain rigorous safety practices for optimum results.

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: D7638 − 10 (Reapproved 2021)
Standard Test Method for
Determination of Fatty Acids and Esters in Glycerin
This standard is issued under the fixed designation D7638; 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 3.1.1 glycerin—propane-1,2,3-Triol, C H (OH) (also
3 5 3
known as glycerine), 1,2,3-propanetriol, 1,2,3-
1.1 This test method provides the quantitative determination
trihydroxypropane, glyceritol, glycyl alcohol. CAS #56-81-5
of the fatty acid and ester content in purified glycerin by the
3.1.2 FA&E—fatty acid and esters
titrimetric method.
3.1.3 For other definitions of terms used in this
1.2 The values stated in SI units are to be regarded as
specification, refer to Terminology D4725.
standard. No other units of measurement are included in this
standard.
4. Significance and Use
1.3 This standard may involve hazardous materials, opera-
4.1 Any residual fatty acid and esters (FA&E) should be
tions and equipment. This standard does not purport to address
present only at very low levels in purified glycerine.
all of the safety concerns, if any, associated with its use. It is
the responsibility of the user of this standard to establish
4.2 This procedure requires the addition of a measured
appropriate safety, health, and environmental practices and
volume of sodium hydroxide, in excess of the amount actually
determine the applicability of regulatory limitations prior to
needed to react with FA&E in the glycerine sample. After
use. Specific precautions are listed in Section 8.
boiling, the excess sodium hydroxide is back titrated with
1.4 This international standard was developed in accor-
standardized hydrochloric acid. The quantity of the substance
dance with internationally recognized principles on standard-
being titrated is calculated as the difference between the
ization established in the Decision on Principles for the
volumes of the sodium hydroxide solution originally added,
Development of International Standards, Guides and Recom-
corrected by means of a blank titration, and that was consumed
mendations issued by the World Trade Organization Technical
by the titrant in the back titration.
Barriers to Trade (TBT) Committee.
NOTE 1—The standardized solutions for sodium hydroxide and hydro-
chloric acid are commercially available.
2. Referenced Documents
2.1 ASTM Standards:
5. Apparatus
D1193 Specification for Reagent Water
5.1 Standard Type A Glassware.
D4725 Terminology for Engine Coolants and Related Fluids
5.2 Erlenmeyer flask, 200 mL to 250 mL, alkali-resistant
2.2 Other Standard:
with a standard tapered 24/40 ground glass neck joint, or
The United States Pharmacopoeia 31 Glycerin Monograph –
equivalent.
Fatty Acids and Esters
5.3 Microburette having a capacity of 5 mL, graduated to
3. Terminology 0.02 mL and calibrated to meet the National Institute of
Standards and Technology (NIST) specification. An automatic
3.1 Definitions:
titrator with a minimum capacity of 5 mL can also be used.
5.4 Pipette, standard or automatic that can accurately de-
This test method is under the jurisdiction of ASTM Committee D15 on Engine liver 5 mL 6 0.01 mL.
Coolants and Related Fluids and is the direct responsibility of Subcommittee
5.5 Air reflux condenser with standard taper ground glass
D15.04 on Chemical Properties.
Current edition approved Sept. 1, 2021. Published September 2021. Originally joint which fits the Erlenmeyer flask in 5.1. Minimum length,
approved in 2010. Last previous edition approved in 2015 as D7638–10 (2015).
550 mm.
DOI: 10.1520/D7638-10R21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
6. Purity of Reagents and Water
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
6.1 Purity of Reagents—Reagent grade chemicals shall be
the ASTM website.
used in all tests. Unless otherwise indicated, it is intended that
Available from U.S. Pharmacopeial Convention (USP), 12601 Twinbrook
Pkwy., Rockville, MD 20852-1790, http://www.usp.org. all reagents conform to the specifications of the Committee on
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7638 − 10 (2021)
and erratic boiling can occur.
Analytical Reagents of the American Chemical Society where
such specifications are available. Other grades may be used
9.4 Add three to five boiling chips into the flask and
provided it is first ascertained that the reagent is of sufficiently
securely place the fitted air condenser into the neck of the flask.
high purity to permit its use without lessening the accuracy of
Using a polytetrafluoroethylene (PTFE) sleeve between the
the determination.
glass joint is suggested.
6.2 Purity of Water—Unless indicated otherwise, references
NOTE 5—When testing samples with expected high FA&E values
to water shall be understood to mean Type II reagent water as
(>0.4), the sample is inclined to foam up the condenser. The addition of
boiling chips helps control this problem.
defined in Specification D1193.
9.5 Place the flask on the heat source and clamp the
NOTE 2—The presence of carbon dioxide can introduce errors; therefore
condenser and flask securely in place. Reflux the solution for a
it is advisable to prepare 500 mL of water by boiling for 5 min. Cool to
room temperature. Check the pH of the distilled water before use. The pH
minimum of 5 min after refluxing has begun.
should be 7.0 6 0.1. If not, adjust the pH with 0.1 N sodium hydroxide
9.6 Carefully remove the flask and condenser assembly
(NaOH) or 0.1 N hydrogen chloride (HCl), whichever is appropriate.
from the heating device and co
...