Lanolin

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

Lanolin is the purified, wax-like substance from the wool of sheep, Ovis aries L. (Fam. Bovidae), that has been cleaned, decolorized, and deodorized. It contains NMT 0.25% of water. It may contain NMT 0.02% of a suitable antioxidant.

2 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.1%

Chloride and Sulfate, Chloride〈221〉

Sample solution: Boil 20 mL of alcohol with 1.0 g of Lanolin under a reflux condenser. Cool, add 1 mL of 2 N nitric acid, and flter. To the filtrate add 5 drops of a solution of 20 mg/mL of silver nitrate in alcohol.

Blank: Boil 20 mL of alcohol under a reflux condenser. Cool, add 1 mL of 2 N nitric acid, and filter. To the filtrate add 5 drops of a solution of 20 mg/mL of silver nitrate in alcohol. Ádd 0.50 mL of 0.020 N hydrochloric acid.

Acceptance criteria: 0.035%; any turbidity produced by the Sample solution does not exceed that produced by the Blank.

Foreign Substances

Use pesticide-free grade reagents and solvents throughout this test. [Note—Reference materials of pesticides for use in the Standard solution may be obtained from any commercial source.1]

Standard stock solutions: Prepare stock solutions for each reference pesticide containing 100 mg/L in hexane.

[Note—Concentrated stock solutions may be stored in glass-stoppered containers in a dark refrigerator at 2°–5° for up to 1 year. Most pesticides may be dissolved directly in hexane; however, the hexachlorocyclohexane isomers and the DDT group of pesticides may require initial dissolution in the minimum volume of acetone followed by dilution with hexane to the specified concentration.]

Standard solution: Dilute volumes of the Standard stock solutions quantitatively with hexane, and combine to obtain a composite Standard solution having the concentrations indicated in Table 1. Store the composite Standard solution in a glass-stoppered glass container in the dark at 2°–5°, and replace it every 2 months. [Note—Two or more separate composite Standard solutions, each preferably containing NMT 8 reference pesticides, may be prepared if needed. Reference pesticides should be selected for composite Standard solutions on the basis that relative retention times (see Table 1) differ suficiently so that peaks in chromatograms will not be expected to overlap, and they should be selected and combined appropriately for the chromatographic system and detector used.]

Table 1

^a Suitable materials may be obtained from either Chem Service, 660 Tower Lane, P.O. Box 3108, Westchester, PA 19381-3108 or Greyhound, 88 Grange Road West, Birkenhead, Merseyside, L43 4XF, England U.K.

Gel permeation chromatography cleanup system

Eluant: Methylene chloride and hexane (1:1)

Column: 25-mm × 50-cm; packed with a slurry of 35 g of styrene–divinylbenzene copolymer beads compressed to a bed length of about 20 cm

Operating pressure: 8–11 psi

Flow rate: 5 mL/min

Set up the chromatograph, adjusting to discard the fraction eluting from 0 to 12 min. Collect the fraction eluting from 12 to 32 min, and rinse for 2 min, discarding the rinse fraction.

System suitability Elution of lanolin: Melt a suitable quantity of Lanolin, and pass through a fluted filter paper into a container. Transfer 6.0 g to a 50-mL volumetric flask. Dilute with Eluant to volume, and filter. Transfer 5.0 mL of this solution to the gel permeation chromatographic column, and elute with Eluant. Collect 100 mL of the column e fluent in tared beakers in 10-mL increments. Evaporate the solvent, cool, weigh the beakers and contents, and calculate the amount of lanolin eluted in each 10-mL increment. The column is suitable if NLT 96% of the lanolin elutes in the first 60 mL.

Elution of pesticide from lanolin: Dissolve suitable quantities of diazinon, diclofenthion, bromophos ethyl, lindane, and dieldrin in hexane to obtain a Standard solution having concentrations of 0.4, 0.4, 1.0, 0.1, and 0.6 μg/mL, respectively. Transfer 5.0 mL of this solution to a 10-mL volumetric flask containing 1 g of USP Lanolin RS. Dilute with methylene chloride to volume. Transfer 5 mL of this solution to the gel permeation chromatographic column, and elute with 160 mL of Eluant. Discard the first 60-mL fraction, and collect the next 100-mL fraction (from 60 to 160 mL). Transfer this collection fraction to a concentrator fitted with a graduated collection flask, add 50 mL of hexane, and concentrate by evaporation to 5 mL. Inject this fraction into the chromatographs described in Chromatographic system I and Chromatographic system II. Record the chromatograms, and measure the heights of the peaks obtained from the five pesticides in the Standard solution. Calculate the recoveries of each of the five pesticides used in the fortified USP Lanolin RS solution.

Prepare a test solution by mixing hexane with the Standard solution (1:1). Inject this into the chromatographs described in Chromatographic system I and Chromatographic system II. Record the chromatograms, and measure the peak heights of the five pesticides in the chromatogram of the Sample solution. Compare the peak heights from the fraction of the Standard solution to the peak heights of the corresponding pesticides from the Sample solution: NLT 85% of the added amounts of each of the five pesticides is recovered.

Sample solution: Transfer 6 g of Lanolin, previously melted to liquid form by heating on a hot water bath if necessary, to a 50-mL volumetric flask. Dissolve in 25 mL of Eluant, dilute with Eluant to volume, and filter. Transfer 5.0 mL of this solution to the column, and elute with 160 mL of Eluant. Discard the first 60-mL fraction, and collect the remaining fraction in a suitable evaporator. Concentrate by evaporation on a steam bath to 3 mL, add 50 mL of hexane, and evaporate again to remove all traces of methylene chloride, adjusting the volume with hexane to 3.0 mL.

Chromatographic system I

(See Chromatography 〈621〉, System Suitability.)

Mode: GC

Detector: Electron capture

Column: 0.53-mm × 30-m fused silica capillary; bonded with a 1.5-μm layer of phase G1, and a 0.53-mm × 6-m fused silica uncoated guard column connected to a modified packed column-type injector system

Column temperature: 200°. [Note—The initial temperature of the column may be adjusted so that the retention times of ethion and p,p′-DDT are 2.56 and 3.1, respectively, relative to chlorpyrifos.]

Carrier gas: Helium

Flow rate: 25 mL/min. Adjust so that the retention time of chlorpyrifos is 4 min.

Makeup gas: Nitrogen, 40 mL per minute

Injection volume: 5 μL

Chromatographic system II

Mode: GC

Detector: Flame photometric

Column: 0.53-mm × 30-m fused silica capillary; bonded with a 1.0-μm layer of phase G3, and a 0.53-mm × 6-m fused silica uncoated guard column connected to a modified packed column-type injector system Column temperature: 200°. [Note—The initial temperature of the column may be adjusted so that the retention time of ethion is 3.36 relative to that of chlorpyrifos.]

Carrier gas: Helium

Flow rate: 25 mL/min. Adjust so that the retention time of chlorpyrifos is 4 min.

Makeup gas: Nitrogen, 40 mL/min

Injection volume: 5 μL

Analysis

The following procedure is to be followed for Chromatographic systems I and II.

Samples: Standard solution and Sample solution

Calculate the quantity of the individual specified residue found in the sample taken:

Result = (r_U/r_S) × (C/W) × 30

r_U = peak area of each residue from the Sample solution

r_S = peak area of each residue from the Standard solution

C = concentration of the reference pesticide in the Standard solution (mg/L)

W = weight of Lanolin taken (g)

Acceptance criteria

Individual specified residue: NMT 10 ppm

Total specified residue: NMT 40 ppm

3 SPECIFIC TESTS

Melting Range or Temperature, Class II〈741〉

Analysis: Determine on a sample previously cooled to 8°–10°.

Acceptance criteria: 38°–44°

Fats and Fixed Oils, Acid Value (Free Fatty Acids)〈401〉

Sample: 10.0 g

Acceptance criteria: The free acids obtained from the Sample require NMT 2.0 mL of 0.10 N sodium hydroxide for neutralization.

Fats and Fixed Oils, Iodine Value〈401〉

Sample: 780–820 mg

Acceptance criteria: 18–36

Alkalinity

Sample: 2.0 g

Analysis: Dissolve the Sample in 10 mL of ether, and add 2 drops of phenolphthalein TS.

Acceptance criteria: The liquid is not colored red.

Water-Soluble Acids and Alkalies

Sample: 10.0 g

Analysis: Warm the Sample with 50 mL of water on a steam bath, constantly stirring the mixture until the Lanolin is melted.

Acceptance criteria: The fat separates completely on cooling, leaving the water layer nearly clear and neutral to litmus. Retain the water layer for the test for Water-Soluble Oxidizable Substances and Ammonia.

Water-Soluble Oxidizable Substances

Sample solution: 10 mL of the solution from Water-Soluble Acids and Alkalies

Analysis: Add the Sample solution to 50 μL of 0.10 N potassium permanganate.

Acceptance criteria: The resulting solution does not completely decolorize within 10 min.

Ammonia

Sample solution: 10 mL of the solution from Water-Soluble Acids and Alkalies

Analysis: Add 1 mL of 1 N sodium hydroxide to the Sample solution, and boil.

Acceptance criteria: The vapors do not turn red litmus to blue.

Water Determination, Method I〈921〉

Solution A: Chloroform and methanol (3:2)

Sample solution: 250 mg/mL of Lanolin in Solution A

Analysis: Determine the water content of a 10.0-mL portion of the Sample solution. Perform a blank determination on 10.0 mL of Solution A, and make any necessary correction.

Acceptance criteria: NMT 0.25%

Petrolatum

Sample: 3 g

Analysis: Heat the Sample on a steam bath, with frequent stirring, until its weight loss is NLT its water content. Boil 40 mL of dehydrated alcohol with 500 mg of the dried lanolin so obtained.

Acceptance criteria: The solution is clear or NMT opalescent.

4 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers, preferably at controlled room temperature.

Labeling: The label states that it is not to be used undiluted.

USP Reference Standards 〈11〉

USP Lanolin RS

1 Suitable materials may be obtained from either Chem Service, 660 Tower Lane, P.O. Box 3108, Westchester, PA 19381-3108 or Greyhound, 88 Grange Road West, Birkenhead, Merseyside, L43 4XF, England U.K.