(les' i thin).
Lecithin is a complex mixture of acetone-insoluble phosphatides, which consist chiefly of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol, combined with various amounts of other substances such as triglycerides, fatty acids, and carbohydrates, as separated from the crude vegetable oil source. It contains NLT 50.0% of acetone-insoluble matter.
Sample: 1 g of Lecithin
Analysis: Transfer the Sample to a Kjeldahl flask, add 5 g of potassium sulfate, 0.5 g of cupric sulfate, and 20 mL of sulfuric acid. Incline the flask to a 45 angle, heat gently until the effervescence almost ceases, and raise the temperature to boiling. After the contents become a blue, transparent solution, heat for 12 h, cool, and add an equal volume of water. To 5 mL of this solution, add 10 mL of ammonium molybdate solution (1 in 5), and heat.
Acceptance criteria: A yellow precipitate is formed.
• B. Paper Chromatography
Standard solution: Choline chloride solution (1 in 200) using USP Choline Chloride RS
Sample solution: To 0.5 g of Lecithin, add 5 mL of hydrochloric acid solution (1 in 2), heat in a water bath for 2 h, and filter.
Developing solvent system: n-Butanol, water, and acetic acid (4:2:1)
Application volume: 10 µL
Spray reagent: Dragendorff's TS
Samples: Standard solution and Sample solution
Use a suitable cellulose filter paper for chromatography. Develop the chromatogram over a path of 25 cm, and dry the paper in a current of air. Spray the paper with Spray reagent to develop a red-orange color, and locate the spots on the paper by examination under daylight.
Acceptance criteria: The RF value of the principal spot from the Sample solution corresponds to that from the Standard solution.
• Content of Acetone-Insoluble Matter
Sample: If the substance under test is plastic or semisolid, soften the Lecithin by warming it briefly at a temperature not exceeding 60, and then mix. Transfer 2 g to a 40-mL centrifuge tube that previously has been tared along with a stirring rod, cool, and weigh.
Analysis: To the Sample add 15.0 mL of acetone, warm carefully in a water bath to melt the test specimen without evaporating the acetone. Stir to help dissolve completely, and place in an ice-water bath for 5 min. Add acetone that has been previously chilled to 05 to the 40-mL mark on the tube, stirring during the addition. Cool in an ice-water bath for 15 min, stir, remove the rod, clarify by centrifuging at about 2000 rpm for 5 min, and decant. Break up the residue with the stirring rod, and refill the centrifuge tube to the 40-mL mark with chilled acetone, while stirring. Cool in an ice-water bath for 15 min, stir, remove the rod, centrifuge, and decant. Break up the residue with the stirring rod. Place the tube in a horizontal position until most of the acetone has evaporated. Mix again, and heat the tube containing the acetone-insoluble residue and the stirring rod at 105 to constant weight. [CautionAcetone is flammable. ]
Determine the weight of the residue, and calculate the percentage of acetone-insoluble matter.
Acceptance criteria: NLT 50.0%
• Heavy Metals, Method II 231: NMT 20 ppm
• Lead 251: NMT 10 ppm
• Hexane-Insoluble Matter
Sample: If the substance under test is plastic or semisolid, soften the Lecithin by warming it at a temperature not exceeding 60, and then mix. Weigh 10.0 g into a 250-mL conical flask.
Analysis: To the Sample add 100 mL of hexanes. Shake until solution is apparently complete or until no more residue seems to be dissolving. Pass through a coarse-porosity filtering funnel that previously has been heated at 105 for 1 h, cooled, and weighed, wash the flask with two 25-mL portions of hexanes, and pour both washings through the funnel. Dry the funnel at 105 for 1 h. [CautionHexane is flammable. ] Cool to room temperature, and determine the gain in weight.
Acceptance criteria: NMT 0.3%
• Fats and Fixed Oils, Acid Value 401
Sample: If the substance under test is plastic or semisolid, soften the Lecithin by warming it briefly at a temperature not exceeding 60, and then mix. Transfer 2 g to a 250-mL conical flask.
Analysis: Dissolve the Sample in 50 mL of petroleum ether. To this solution add 50 mL of alcohol, previously neutralized to phenolphthalein with 0.1 N sodium hydroxide, and mix. Add phenolphthalein TS. Titrate with 0.1 N sodium hydroxide VS to a pink endpoint that persists for 5 s.
Calculate the amount, in mg, of potassium hydroxide required to neutralize the free acids in 1.0 g of the Lecithin:
Result = (MR × N × V)/W
Acceptance criteria: NMT 36
• Peroxide Value
Sample: 5 g of Lecithin
Analysis: Transfer the Sample into a 250-mL Erlenmeyer flask with a ground-glass stopper, add 35 mL of a mixture of chloroform and acetic acid (2:1), and mix. Completely dissolve the test specimen while shaking gently. The solution becomes transparent. Completely replace the air in the flask with nitrogen. While purging with nitrogen, add 1 mL of potassium iodide solution (165 mg/mL of potassium iodide), then stop the flow of the nitrogen, and immediately place a stopper in the flask. Shake for 1 min, and allow to stand in a dark place for 5 min. Add 75 mL of water, replace the stopper again, and shake vigorously. Titrate with 0.01 N sodium thiosulfate VS, adding starch TS as the endpoint is approached, and continue the titration until the blue starch color has just disappeared. Perform a blank determination (see Titrimetry 541), and make any necessary correction.
Calculate the peroxide value, as milliequivalents of peroxide per 1000 g of Lecithin:
Result = (S × N/W) × 1000
Acceptance criteria: NMT 10
• Water Determination, Method I 921: NMT 1.5%
• Packaging and Storage: Preserve in well-closed, light-resistant containers. Store at the temperature indicated on the label. Protect from excess heat and moisture.
• Labeling: Label it to indicate the storage conditions.
• USP Reference Standards 11
Auxiliary Information Please check for your question in the FAQs before contacting USP.
USP35NF30 Page 1841Pharmacopeial Forum: Volume No. 33(6) Page 1249