DETECTION OF ACETINS

6. DETECTION OF ACETINS

The acetic acid esters of glycerin are occasionally employed as adulterants in order to increase the apparent ester content. Since all three acetins are relatively soluble in water they may easily be washed out and tested for by the procedure described below. The least soluble of the three is triacetin; even this, however, is soluble in water to the extent of about 7 per cent. In order to insure the removal of most of the triacetin, a 5 per cent alcoholic solution is employed.
Procedure:194 Shake 20 cc. of the oil with 40 cc. of 5% alcohol in a 125 cc. glass-stoppered, separatory funnel. When the mixture has separated completely withdraw 30 cc. of the alcoholic solution by means of a pipette and place it in a 125 cc. Erlenmeyer flask. Neutralize the solution with 0.5 N sodium hydroxide, using a 1% phenolphthalein solution as indicator. Then add exactly 5 cc. of 0.5 N alcoholic sodium hydroxide and heat the mixture on a steam bath for 1 hr. Remove the flask and allow the mixture to cool. Titrate the excess of alkali with 0.5 N hydrochloric acid. At least 4.7 cc. of the acid should be used for this neutralization.
This test is not specific for acetins; if large amounts of other watersoluble esters are present, these will appear in the dilute alcoholic layer.
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194 The procedure as given is essentially that of "The United States Pharmacopoeia," Thirteenth Revision, 285, described under Oil of Lavender.

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