ASTM D7638-10(2021)

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 service@astm.org. 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
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