DETERMINATION OF ETHYL ALCOHOL CONTENT OF TINCTURES AND ESSENCES

10. DETERMINATION OF ETHYL ALCOHOL CONTENT OF TINCTURES AND ESSENCES

The determination of the content of ethyl alcohol in essences, tinctures and alcoholic extracts is frequently necessary. Because of the presence of volatile esters and essential oils, a determination by distillation alone is usually impossible. Consequently these interfering substances must be removed by washing with heptane or petroleum ether before such distillation is attempted. The two procedures given below give satisfactory results :

Procedure Method I: Pipette 25 cc. of the sample into a 500 cc. scparatory funnel, noting the temperature. Add 100 cc. of a saturated salt solution and 100 cc. of petroleum ether. Shake thoroughly for 2 to 3 min., and permit the mixture to stand undisturbed until a good separation is obtained (usually within 5 to 60 min.).¹⁵⁷

DIAGRAM 4.15. Apparatus for thedetermination of alcohol.

Draw off the salt solution into a 1 liter distilling flask. Wash the petroleum ether layer with two successive 35 cc. portions of saturated salt solution, adding both washings to the solution in the distilling flask. Discard the petroleum ether layer. Add 100 cc. water to the contents of the distilling flask; also a small amount of solid phenolphthalein and enough 10% aqueous sodium hydroxide solution to make the contents alkaline to the indicator. Also add a few small clay chips and slowly distill until a distillate of about 70 cc. has been collected in a 100 cc. volumetric flask immersed in a beaker of cold water (use a straight tube water-cooled condenser). Add enough distilled water to make the volume up to about 90 cc. If the distillate remains water-white (or at most has a faint opalescence not a turbidity), adjust the temperature to that originally observed and make up to 100 cc.¹⁵⁸

Determine the specific gravity accurately and, from this, the alcohol percentage by volume (see Table 4.16). Multiply by 4 to obtain the alcohol content of the original material. If this value is above 25%,159 determine the refractive index at 20 and compare with the value given in Table 4.17. The calculated index should not differ by more than 0.0002 from the experimentally determined value. A larger difference indicates the presence of some interfering substance in the alcoholic distillate. The determination should then be repeated, using the double distillation procedure previously described in footnote¹⁵⁸.

Procedure Method II. Into a 500 cc. Erlenmeyer flask pipette 25 cc. of the sample and add 50 cc. of distilled water and 25 cc. of n-heptane. To the 250 cc. separatory funnel add 40 cc. of n-heptane and connect the distilling tube and reflux condenser as shown in Diagram 4.15. Heat gently and distill slowly until 40 cc. of distillate have been collected under the heptane layer in the separatory funnel. Permit the contents of the funnel to stand undisturbed for 15 min. to attain room temperature and drain the distillate into a 50 cc. volumetric flask. Wash the residual heptane with two 4 cc. portions of distilled water, adding these washings to the volumetric flask. Fill the flask to the mark and determine the specific gravity of the mixture and calculate the alcoholic percentage by means of Table

salt solution and add these washings to the distilling flask. Add 100 cc. of water, a small amount of solid phenolphthalein, and make alkaline with 10 per cent sodium hydroxide solution. Continue as before, collecting a distillate of about 70 w. If a turbid solution is again obtained resort to the heptane distillation method (see "Procedure, Method II").

TABLE 4.16. ALCOHOLOMETRIC TABLE*

TABLE 4.16. Continued

TABLE 4.16. Continued

It should be noted that certain low boiling, water-soluble constituents, such as acetic acid and acetone, will interfere in such a determination. However, most low boiling esters are readily absorbed by the heptane layer.

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156 The weight of sample can be determined conveniently by placing approximately the amount of oleoresin required in a graduate and weighing before and after the sample has been introduced into the flask.

157 If a sharp separation is not obtained pipette a 25 cc. sample into a 1 liter distilling flask, add 500 cc. of water and distill. Collect 100 cc. of distillate in a 250 cc. separatory funnel, saturate with salt, add 100 cc. petroleum ether, and shake thoroughly. After the layers have separated continue as directed in the second paragraph of the procedure. The heptane distillation method may also be used (see "Procedure, Method II").

158 If a turbid solution is obtained, transfer the distillate completely from the volumetric flask with the aid of distilled water into a 250 cc. separatory funnel. Add 50 cc. of petroleum ether and shake thoroughly. (It may be necessary to add enough salt to saturate the wateralcohol mixture in order to get a sharp separation.) When a sharp separation is obtaine (this usually takes from 15 to 60 min.), draw off the lower layer into a 1 liter distilling flask. Wash the petroleum ether layer successively with a 50 cc. and a 25 cc. portion of saturated

159 If the alcoholic percentage is less than 25 per cent, pipette 50 cc. of the distillate into a 500 cc. distilling flask, add 100 cc. distilled water, a few clay chips, and distill slowly until a distillate of 20 cc. has been collected in a 25 cc. volumetric flask. Adjust the temperature and make up to 25 cc. Continue as before, but multiply by 2 (instead of 4) to obtain the alcohol percentage in the original material. 4.16. Multiply by 2 in order to obtain the alcohol content of the original material.