Ethanolic potassium hydroxide— Dissolve about 5.5 g of potassium hydroxide in absolute alcohol, heating if necessary to effect solution, and dilute with absolute alcohol to about 1000 mL. Prepare fresh daily, and filter if necessary to remove carbonate.

Procedure— Transfer about 450 mg of Sodium Stearyl Fumarate, accurately weighed, to a 300-mL conical flask, and add 50.0 mL of Ethanolic potassium hydroxide, rinsing down the inside of the flask during the addition. Gently reflux the mixture on a steam bath for not less than 2 hours, swirling gently occasionally, but avoid splashing the mixture up into the condenser. Rinse the condenser with 10 mL of 70 percent alcohol, followed by three 10-mL portions of water, collecting the rinsings in the flask. Cool, rinse the sides of the flask with two 10-mL portions of 70 percent alcohol, add phenolphthalein TS, and titrate with 0.1 N hydrochloric acid VS to the disappearance of any pink color. Perform a blank determination, using the same volume of Ethanolic potassium hydroxide. The difference between the volumes, in mL, of 0.1 N hydrochloric acid consumed in the actual test and in the blank test, multiplied by 5.61 and divided by the weight, in g, of specimen taken, is the Saponification value. It is between 142.2 and 146.0, calculated on the anhydrous basis.

Standard monostearyl maleate preparation— Using a mixture of chloroform and glacial acetic acid (4:1) as solvent, prepare a solution of USP Monostearyl Maleate RS containing 1 mg per mL. Pipet 5 mL of this solution into a 50-mL volumetric flask, dilute with chloroform to volume, and mix.

Standard stearyl alcohol preparation— Using a mixture of chloroform and glacial acetic acid (4:1) as solvent, prepare a solution of USP Stearyl Alcohol RS containing 1 mg per mL. Pipet 5 mL of this solution into a 50-mL volumetric flask, dilute with chloroform to volume, and mix.

Test preparation— Weigh 200 mg of Sodium Stearyl Fumarate into a small, glass-stoppered conical flask. Add 10.0 mL of a mixture of chloroform and glacial acetic acid (4:1). Dissolve by placing the flask in an ultrasonic bath for about 10 minutes.

Procedure— Apply 5 µL of Standard monostearyl maleate preparation and 10 µL each of Standard stearyl alcohol preparation and Test preparation separately to a thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel. Immerse the plate in a tank containing a layer of about 10 mm of chloroform on the bottom. Allow the solvent front to reach the upper edge of the spots. Withdraw the plate, and dry in a current of cold air. Repeat the immersion, development, and drying. This results in spots having a linear shape. Develop the chromatograph in a saturated chamber containing a solvent system consisting of a mixture of hexanes, toluene, and glacial acetic acid (50:50:10) until the solvent front has moved 15 cm, and remove the plate from the chamber. Allow to dry for 10 minutes, and heat in an oven at 90 for 2 minutes. Allow to cool to room temperature. Replace the plate into the chamber for another 15-cm development, remove the plate, and allow to dry at room temperature for 15 minutes. Spray the plate carefully with a solution prepared by adding, cautiously and with stirring, 10 mL of sulfuric acid to 90 mL of alcohol. Dry the plate in an oven at 150 for 15 minutes. Dark spots appear on a light background. Allow to cool. Faint spots at an RF value of about 0.9 may result from traces of distearyl maleate and distearyl fumarate. The intensity of any spot from the Test preparation is not greater than that from the corresponding spot from the Standard preparation (0.25% sodium stearyl maleate, 0.5% stearyl alcohol).