Palmitic Acid

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

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Palmitic Acid is a mixture of fatty (2S (NF36)) acids obtained from fats or oils of animal or vegetable origin. It contains NLT 92.0% of palmitic acid (C₁₆H₃₂O₂) and NMT 6.0% of stearic acid (C₁₈H₃₆O₂).

2 IDENTIFICATION

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A. CHROMATOGRAPHIC IDENTITY: (2S (NF36)) The retention time of the major peak for palmitic acid of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

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B. Acid Value

Sample: 1 g of Palmitic Acid

Analysis: Proceed as directed in Fats and Fixed Oils 〈401〉, Procedures, Acid Value. Acceptance criteria: 216–220 (2S (NF36))

3 ASSAY

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3.1 PROCEDURE

Solution A: Add 1 mL of phosphoric acid to 1 L of water. This is a 0.1% phosphoric acid solution.

Solution B: Acetonitrile

Diluent: Methanol

Mobile phase: See Table 1.

Table 1

System suitability solution: 5.0 mg/mL of USP Myristic Acid RS and 0.025 mg/mL of linolenic acid in Diluent Standard solution: 5.0 mg/mL of USP Palmitic Acid RS in Diluent

Sample solution: 5.0 mg/mL of Palmitic Acid in Diluent

3.1.1 Chromatographic system

(See Chromatography 〈621〉, System Suitability.) Mode: LC

Detector: UV 210 nm

Column: 4.6-mm × 15-cm; 2.7-µm packing L1

Column temperature: 40°

Flow rate: 1.0 mL/min

Injection volume: 25 µL

Run time: 30 min

3.1.2 System suitability

Samples: System suitability solution and Standard solution

[NOTE—The relative retention times for linolenic acid, myristic acid, and palmitic acid are 0.77, 0.80, and 1.00, respectively.]

Suitability requirements

Resolution: NLT 1.5 between linolenic acid and myristic acid, System suitability solution

Tailing factor: 0.8–1.5, Standard solution

Relative standard deviation: NMT 0.5%, Standard solution

3.1.3 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of palmitic acid (C₁₆H₃₂O₂) in the portion of Palmitic Acid taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response from the Sample solution

r_S = peak response from the Standard solution

C_S = concentration of USP Palmitic Acid RS in the Standard solution (mg/mL)

C_U = concentration of Palmitic Acid in the Sample solution (mg/mL)

Acceptance criteria: NLT 92.0% of palmitic acid (C₁₆H₃₂O₂) (2S (NF36))

4 IMPURITIES

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HEAVY METALS, Method II 〈231〉: NMT 10 ppm  (Official 1-Jan-2018)

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Limit of Stearic Acid, Myristic Acid, and Other Related Fatty Acids

Solution A, Solution B, Diluent, Mobile phase, System suitability solution, and Chromatographic system: Proceed as directed in the Assay. Standard solution: 0.3 mg/mL of USP Stearic Acid RS, 0.1 mg/mL of USP Myristic Acid RS, and 0.05 mg/mL of USP Palmitic Acid RS in Diluent

Sample solution: 5.0 mg/mL of Palmitic Acid in Diluent

3.1.4 System suitability

Samples: System suitability solution and Standard solution

[NOTE—The relative retention times for linolenic acid, myristic acid, palmitic acid, and stearic acid are 0.77, 0.80, 1.00, and 1.17, respectively.]

Suitability requirements

Resolution: NLT 1.5 between linolenic acid and myristic acid, System suitability solution Relative standard deviation: NMT 5%, Standard solution

3.1.5 Analysis

Samples: Standard solution and Sample solution

Based on the Standard solution and Table 2, identify the peaks of appropriate fatty acids. [NOTE—The relative retention times for several fatty acids are provided in Table 2.]

Table 2

Calculate the percentage of myristic acid (C₁₄H₂₈O) or stearic acid (C₁₈H₃₆O₂) in the portion of Palmitic Acid taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of myristic acid or stearic acid from the Sample solution

r_S = peak response of myristic acid or stearic acid from the Standard solution

C_S = concentration of USP Myristic Acid RS or USP Stearic Acid RS in the Standard solution (mg/mL)

C_U = concentration of Palmitic Acid in the Sample solution (mg/mL)

Calculate the percentage of any other single fatty acid (caprylic acid, capric acid, or lauric acid, if present) in the portion of Palmitic Acid taken:

Result = (r_U/r_S) × (C_S/C_U) × (1/F) × 100

r_U = peak response of any other single fatty acid (caprylic acid, capric acid, or lauric acid, if present) from the Sample solution

r_S = peak response of palmitic acid from the Standard solution

C_S = concentration of USP Palmitic Acid RS in the Standard solution (mg/mL)

C_U = concentration of Palmitic Acid in the Sample solution (mg/mL)

F = relative response factor for any other single fatty acid (caprylic acid, capric acid, or lauric acid, if present) (see Table 2)

Acceptance criteria: Disregard peaks that are less than 0.05% for any individual impurity, and any peaks due to solvents.

Stearic acid: NMT 6.0%

Myristic acid: NMT 2.0%

Any other single fatty acid (caprylic acid, capric acid, or lauric acid): NMT 1.0% (2S (NF36))

5 SPECIFIC TESTS

COLOR: Heat a sample of Palmitic Acid to 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〉).

CONGEALING TEMPERATURE 〈651〉: 60°–66°

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FATS AND FIXED OILS, Acid Value 〈401〉: 216–220, using 1 g (2S (NF36))

FATS AND FIXED OILS 〈401〉 , Procedures, Iodine Value, Method I

Analysis: Proceed as directed in the chapter, except use 35 mL of chloroform. Acceptance criteria: NMT 1

MINERAL ACID

Analysis: Shake 5 g of melted Palmitic Acid with an equal volume of hot water for 2 min. Cool, and filter. Acceptance criteria: The filtrate is not reddened by the addition of 1 drop of methyl orange TS.

6 ADDITIONAL REQUIREMENTS

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. Change to read:

USP REFERENCE STANDARDS 〈11〉

USP Myristic Acid RS (2S (NF36))

USP Palmitic Acid RS USP Stearic Acid RS