Gel permeation chromatography cleanup system—

ELUANT: methylene chloride.

APPARATUS —The gel permeation chromatograph is equipped with a 25-mm × 100-cm column, packed with a slurry of styrene-divinylbenzene copolymer beads compressed to a bed length of approximately 77 cm. The Eluant is pumped at a flow rate of about 4 mL per minute. Set up the chromatograph, adjusting to discard the fraction eluting from 0 to 43 minutes, collect the fraction eluting from 43 to 60 minutes, and rinse for 20 minutes, discarding the rinse fraction.

System suitability—

ELUTION OF LANOLIN ALCOHOLS —Melt a suitable quantity of USP Lanolin Alcohols RS, and pass through a fluted filter paper into a container. Transfer about 1.0 g of warm filtered USP Lanolin Alcohols RS, accurately weighed, to a 10-mL volumetric flask. Dilute with Eluant to volume, and mix. Transfer 5 mL of this Standard solution to the gel permeation chromatographic column, and elute with Eluant. Collect 172 to 240 mL of the column effluent in a suitable evaporator. Evaporate the solvent, cool, weigh the evaporator, and calculate the amount of lanolin alcohols eluted in the evaporator. The column is suitable if not less than 99% of the lanolin alcohols elute in the first 172 to 240 mL.

Standard preparation— Dissolve a suitable quantity of USP Lanolin Alcohols RS, accurately weighed, in hexane, with the aid of warming if necessary, to obtain a solution having a known concentration of about 0.5 mg per mL. [NOTE—Store this solution in the dark in a cold place for up to 4 weeks. Before using, warm just sufficiently to dissolve any precipitate if necessary.]

Test preparation— Transfer 1 g of Modified Lanolin, accurately weighed and previously melted to liquid form, by heating on a hot water bath if necessary, to a 10-mL volumetric flask, dissolve in 7 mL of Eluant, dilute with Eluant to volume, mix, and filter. Transfer 5.0 mL of this solution to the column, and elute with 320 mL of Eluant. Discard the first 172-mL fraction, collect the next 68-mL fraction (from 172 to 240 mL) in a suitable evaporator. Concentrate by evaporation on a steam bath to about 3 mL, add about 50 mL of hexane, and transfer this solution to a 100-mL volumetric flask, adjusting the volume with hexane to 100 mL.

Chromatographic system— The gas chromatograph is equipped with a flame-ionization detector maintained at 290, a 0.33-mm × 50-m fused silica capillary column bonded with a 0.50-µm layer of phase G2, a 0.32-mm × 50-cm fused silica uncoated guard column to protect the main analytical column. The column temperature is initially held at 210 and programmed to rise to 280 at the rate of 3 per minute. Nitrogen is used as the carrier gas at a flow rate of about 7 mL per minute, and is also used as the makeup gas at a flow rate of about 50 mL per minute.

Procedure— Separately inject equal volumes (about 1 µL) of the Standard preparation and the Test preparation into the chromatograph, and allow both the Standard preparation and the Test preparation to elute for not less than 40 minutes. Record the chromatograms, and measure the areas of all of the peaks. Calculate the quantity, in percentage, of free lanolin alcohols in the portion of Modified Lanolin taken by the formula: in which rU and rS are the total peak areas found in the Test preparation and the Standard preparation, respectively; C is the concentration, in mg per mL of USP Lanolin Alcohols RS in the Standard preparation; I is the volume, in mL, injected into the gel permeation chromatography column; W is the weight, in g, of Modified Lanolin taken; and K is the corrected fraction of free lanolin alcohols in the USP Lanolin Alcohols RS in the Standard preparation taken by the formula: in which A and S are the acid value and saponification value, respectively, of USP Lanolin Alcohols RS: not more than 6% is found.

(Official January 1, 2007)