A: Thin-Layer Chromatographic Identification Test 201—

B: It complies with the requirements of the test for Fatty acid composition.

Fatty Acids	Carbon-Chain Length	Percentage (%)
Caprylic acid	C8	not more than 0.5
Capric acid	C10	not more than 2.0
Lauric acid	C12	not less than 95.0
Myristic acid	C14	not more than 3.0
Palmitic acid	C16	not more than 1.0

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: 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.

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 (100). 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 Dilaurate taken by the formula: 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: in which A is the acid value.