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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