ASTM D7638-10(2015)

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Designation: D7638 − 10 D7638 − 10 (Reapproved 2015)
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
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 the standard. The values given in parentheses are for information
only.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 and health practices and determine the applicability of regulatory limitations prior to use. Specific precautions are listed
in Section 8.
2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
D4725 Terminology for Engine Coolants and Related Fluids
2.2 Other Standards:Standard:
The United States Pharmacopoeia 31 Glycerin Monograph – Fatty Acids and Esters
3. Terminology
3.1 Definitions:
3.1.1 glycerin—propane-1,2,3-Triol, C H (OH) (also known as glycerine), 1,2,3-propanetriol, 1,2,3-trihydroxypropane,
3 5 3
glyceritol, glycyl alcohol. CAS #56-81-5
3.1.2 FA&E—Fatty acid and Esters
3.1.3 For other definitions of terms used in this specification, refer to Terminology D4725.
4. 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.
5. Apparatus
5.1 Standard Type A Glassware.
5.2 Erlenmeyer flask, 200 to 250 mL, alkali-resistant with a standard tapered 24/40 ground glass neck joint, or equivalent.
This test method is under the jurisdiction of ASTM Committee D15 on Engine Coolants and Related Fluids and is the direct responsibility of Subcommittee D15.93 on
Research and Long Range Planning.
Current edition approved June 1, 2010May 1, 2015. Published July 2010June 2015. Originally approved in 2010. Last previous edition approved in 2010 as D7638–10.
DOI: 10.1520/D7638–10.10.1520/D7638–10R15.
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volume information, refer to the standard’s Document Summary page on the ASTM website.
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D7638 − 10 (2015)
5.3 Microburette having a capacity of 5 mL, graduated to 0.02 mL and calibrated to meet the NIST specification. An automatic
titrator with a minimum capacity of 5 mL can also be used.
5.4 Pipette, standard or automatic that can accurately deliver 5 6 0.01 mL.
5.5 Air reflux condenser with standard taper ground glass joint which fits the Erlenmeyer flask in 5.1. Minimum length, 550 mm.
6. Purity of Reagents and Water
6.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such
specifications are available. Other grades may be used provided it is first ascertained that the reagent is of sufficiently high purity
to permit its use without lessening the accuracy of the determination.
6.2 Purity of Water—Unless indicated otherwise, references to water shall be understood to mean Type II reagent water as
defined in Specification D1193.
NOTE 2—The presence of carbon dioxide can introduce errors; therefore 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 should be 7.0 6 0.1. If not, adjust the pH with 0.1 N sodium hydroxide (NaOH)
or 0.1 N hydrogen chloride (HCl), whichever is appropriate. Store the freshly boiled and neutralized water in a tightly closed container.
7. Reagents
7.1 Phenolphthalein Solution—(See Note 2.) Dissolve 1 g of phenolphthalein in 100 mL of ethanol (95 %), methanol or
isopropanol. This solution can be purchased.
7.2 Hydrochloric Acid, 0.5 N, aqueous solution—(See Note 1 and Note 2.) To a 1000-mL volumetric flask containing 40 mL
of water, slowly add 43 mL of concentrated hydrochloric acid. Cool, and add water to volume. Standardize the solution to an
accuracy of 60.001 N.
7.3 Sodium Hydroxide, 0.5 N, aqueous solution—(See Note 1 and Note 2.) Dissolve 22.0 g of NaOH in water and dilute to 1
L. Allow to stand overnight. Siphon the liquid into a clean bottle. Standardize accurately to 60.001 N with potassium acid
phthalate. The standardized sodium hydroxide solution should be protected against evaporation and absorption of carbon dioxide
(CO ) fr
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