ASTM D7638-10

Any residual fatty acid and esters (FA&E) should be present only at very low levels in purified glycerine.

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.

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.

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.