Identification—
B:
Standard preparation—Transfer 33 mg of
USP Isosorbide RS, 25 mg of
USP 1,4-Sorbitan RS, and 25 mg of sorbitol to a 1-mL volumetric flask, dilute with water to volume, and mix to dissolve.
Test preparation—
Transfer 500 mg of the polyols obtained in the
Assay for polyols to a 2-mL volumetric flask, dilute with water to volume, and mix to dissolve.
Procedure—
Apply 2 µL each of the
Standard preparation and of the
Test preparation to a suitable thin-layer chromatographic plate (see
Chromatography 
621
) coated with a 0.25-mm layer of chromatographic silica gel. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of a mixture of acetone and glacial acetic acid (50:1) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate. Spray evenly with a mixture of equal volumes of sulfuric acid and water until the surface is uniformly wet (do not overspray), and immediately place the sprayed plate on a 200
hot plate
in a well-ventilated hood. Char until white fumes of sulfur trioxide cease, and cool: the
RF values of the spots obtained from the
Test preparation correspond to those of the spots obtained from the
Standard preparation.
Assay for fatty acids—
Transfer about 10 g of Sorbitan Monooleate, accurately weighed, to a 500-mL conical flask, cautiously add 100 mL of alcohol and 3.5 g of potassium hydroxide, then add a few glass beads, and mix. Connect a suitable condenser to the flask, reflux the mixture on a hot plate for 2 hours, add about 100 mL of water, and heat on a steam bath to evaporate the alcohol, adding water occasionally to replace the alcohol. Continue the evaporation until the odor of alcohol can no longer be detected, and transfer the saponification mixture, with the aid of about 100 mL of hot water, to a 500-mL separator. Using extreme caution, neutralize to litmus with a mixture of equal volumes of sulfuric acid and water, noting the volume used, and add a 10% excess of the dilute acid. Allow the solution to cool. If salts appear, add sufficient water to produce a clear solution. Cautiously add 100 mL of solvent hexane, shake thoroughly, and withdraw the lower layer into a second 500-mL separator. Similarly extract with 2 more 100-mL portions of solvent hexane. Extract the combined hexane layers with 50-mL portions of water until neutral to litmus paper, and combine the extracts with the original aqueous phase, for the
Assay for polyols. Evaporate the solvent hexane in a tared beaker on a steam bath nearly to dryness, dry in vacuum at 60
for 1 hour, cool in a desiccator, and weigh the fatty acids.
Assay for polyols—
Neutralize the aqueous solution of polyols retained from the
Assay for fatty acids with potassium hydroxide solution (1 in 10) to a pH of 7, using a suitable pH meter. Evaporate on a steam bath to a moist residue, extract the polyols from the salts with three 150-mL portions of dehydrated alcohol, boiling the salt residue for 3 minutes, and crushing it, as necessary, with the flattened end of a stirring rod, during each extraction, filtering each extract, while hot, through a medium-porosity, sintered-glass funnel, provided with a sheet of retentive filter paper on which a layer of purified siliceous earth has been superimposed, and receiving the filtrates in a 1-liter suction flask. Transfer the clear alcoholic polyols solution to a tared beaker, evaporate the alcohol on a steam bath, dry in vacuum at 60
for 1 hour, cool in a desiccator, and weigh the polyols.
