Identification—
A: Thin-Layer Chromatographic Identification Test 
201
—
Test solution:
50 mg per mL, in methylene chloride.
Developing solvent solution:
a mixture of hexane and ether (30:70).
Spray reagent—
Prepare a 0.1 mg per mL solution of rhodamine 6G in alcohol.
Procedure—
Develop the chromatogram over a path of 15 cm, and dry the plate in a current of air. Spray the plate with Spray reagent, and locate the spots on the plate by examination under UV light at a wavelength of 365 nm: the RF values of the principal spots obtained from the Test solution correspond to those obtained from the Standard solution.
B:
It complies with the requirements of the test for Fatty acid composition.
Limit of propylene glycol—
Mobile phase—
Proceed as directed in the Assay.
Propylene glycol standard stock solution—
Prepare a solution containing a known concentration of about 4 mg per mL of
USP Propylene Glycol RS in tetrahydrofuran.
Propylene glycol standard solutions—
Into four 15-mL flasks, introduce respectively 0.25 mL, 0.5 mL, 1.0 mL, and 2.5 mL of Propylene glycol standard stock solution, and dilute with tetrahydrofuran to 5.0 mL. In a fifth 15-mL flask, introduce 5.0 mL of Propylene glycol standard stock solution.
Test solution—
Use the Assay preparation.
Chromatographic system—
Proceed as directed in the Assay.
Procedure—
Separately inject equal volumes (about 40 µL) of the
Propylene glycol standard solutions and the
Test solution into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Prepare a standard curve of peak area versus concentration, in mg per mL, of propylene glycol in the
Propylene glycol standard solutions. Obtain the concentration,
C, in mg per mL, of propylene glycol in the
Test solution from the standard curve. Calculate the percentage of free propylene glycol in the portion of Propylene Glycol Dilaurate taken by the formula:
100CV/W
in which
V is the final volume of the
Test solution; and
W is the weight, in mg, of Propylene Glycol Dilaurate used to prepare the
Test solution: not more than 2.0% is found.
Assay—
Mobile phase:
tetrahydrofuran.
Assay preparation—
Accurately weigh about 200 mg of Propylene Glycol Dilaurate into a 15-mL flask, add 5 mL of tetrahydrofuran, and shake to dissolve.
Chromatographic system (see Chromatography 621)—
The liquid chromatograph is equipped with a refractive index detector and a 7-mm × 60-cm column that contains 5-µm packing L21 (100Å). The flow rate is about 1 mL per minute. The column and detector temperatures are maintained at 40
.
[NOTE—Two 7-mm × 30-cm L21 columns may be used in place of one 60-cm column, provided system suitability requirements are met.
] Chromatograph the
Assay preparation, and record the peak responses as directed for
Procedure: the order of elution is diesters, monoesters, and propylene glycol; and the relative standard deviation for replicate injections determined from the monoester peak is not more than 1.0%.
Procedure—
Inject a volume (about 40 µL) of the
Assay preparation into the chromatograph, record the chromatogram, and measure the responses for the major peaks. Calculate the percentage of monoesters or diesters in the portion of Propylene Glycol Monolaurate taken by the formula:
(100
D)(
rU /
rs)
in which
D is the sum of the percentage content of propylene glycol and the percentage content of free fatty acids;
rU is the peak response for monoesters or diesters; and
rs is the sum of the responses of the monoesters and diesters peaks. Calculate the percentage content of free fatty acids using the formula:
200(A/561.1)
in which
A is the acid value.
NF24
