Hexadecanoic acid [57-10-3].
» Palmitic Acid is a mixture of solid organic acids obtained from fats or oils of animal or vegetable origin. It contains not less than 92.0 percent of C16H32O2 and not more than 6.0 percent of stearic acid (C18H36O2).
Packaging and storage Preserve in well-closed containers, and store at room temperature.
Labeling Label it to indicate whether it is derived from animal or vegetable sources.
Color Heat it to about 75. The resulting liquid is not more intensely colored than a solution prepared by mixing 1.2 mL of ferric chloride CS and 0.3 mL of cobaltous chloride CS with 0.3 N hydrochloric acid to make 10 mL, and diluting 5 mL of this solution with 0.3 N hydrochloric acid to make 100 mL. Make the comparison by viewing the solutions downward in matched color-comparison tubes against a white surface (see Color and Achromicity 631).
Identification The retention time of the major peak for palmitic acid in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.
Congealing temperature 651: between 60 and 66.
Acid value 401: between 216 and 220, using about 1 g, accurately weighed.
Iodine value 401: not more than 1. Proceed as directed in Method I except to use 35 mL of chloroform.
Mineral acid Shake 5 g of melted Palmitic Acid with an equal volume of hot water for 2 minutes, cool, and filter: the filtrate is not reddened by the addition of 1 drop of methyl orange TS.
Heavy metals, Method II 231: 0.001%.
Standard preparation Prepare the Standard preparation in the same manner as the Assay preparation, using a mixture of 50 mg of USP Palmitic Acid RS and 50 mg of USP Stearic Acid RS instead of the substance to be examined.
Assay preparation Proceed as directed for Test Solution in Fatty Acid Composition under Fats and Fixed Oils 401.
Chromatographic system (see Chromatography 621) Prepare as directed for Fatty Acid Composition under Fats and Fixed Oils 401. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are about 0.9 for methyl palmitate and 1.0 for methyl stearate; the resolution, R, between methyl stearate and methyl palmitate is not less than 3.0.
Procedure Separately inject equal volumes (about 1 µL) of the Assay preparation and the Standard preparation into the chromatograph, record the chromatograms, identify the methyl palmitate peak in the chromatogram obtained from the Assay preparation by comparing the retention times of the peaks in that chromatogram with those in the chromatogram obtained from the Standard preparation, and measure the responses for all the peaks, excluding the solvent peak. Calculate the percentage of C16H32O2 in the portion of Palmitic Acid taken by the formula:
100A/Bin which A is the methyl palmitate peak response; and B is the sum of the responses of all the peaks in the chromatogram except the solvent peak. Similarly calculate the percentage of stearic acid in the portion of Palmitic Acid taken.
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USP32NF27 Page 1295Pharmacopeial Forum: Volume No. 30(3) Page 987