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Microcrystalline Wax
» Microcrystalline Wax is a mixture of straight-chain, branched-chain, and cyclic hydrocarbons, obtained by solvent fractionation of the still bottom fraction of petroleum by suitable dewaxing or deoiling means.
Packaging and storage— Preserve in tight containers.
Labeling— Label it to indicate the name and proportion of any added stabilizer.
Color— Melt about 10 g on a steam bath, and pour 5 mL of the liquid into a clear-glass, 16- × 150-mm bacteriological test tube: the warm, melted liquid is not darker than a solution made by mixing 3.8 mL of ferric chloride CS and 1.2 mL of cobaltous chloride CS in a similar tube, the comparison of the two being made in reflected light against a white background, the tubes being held directly against the background at such an angle that there is no fluorescence.
Melting range, Class III 741 : between 54 and 102.
Apparatus— Determine the consistency of Microcrystalline Wax by means of a penetrometer fitted with a polished metal needle weighing 2.5 ± 0.05 g and having a truncated symmetric tapered angle of 910¢ ± 15¢. The needle is tapered, with a length of 25.4 mm, and the shaft attached to the needle is 58 mm in length and 3.17 mm in diameter. The plunger that fits into the penetrometer and guides the path of the needle weighs 47.5 ± 0.05 g. An additional weight of 50 ± 0.05 g is added to the top of the plunger to give a total load of 100 g.
Procedure— The wax specimen is cast in a brass cylinder open at both ends. The cylinder has an inside diameter of 25.4 mm and is 31.8 mm in height. Place the cylinder on a brass plate wetted with an equal volume mixture of glycerin and water, and place the plate on two corks. Pour the wax, melted at approximately 17 above its congealing point, into the cylinder. Continue pouring the wax until a convex meniscus is formed above the cylinder. Allow the specimen to cool for 1 hour at approximately 24. Shave excess wax from the top of the cylinder, and remove the plate. With the smooth wax surface in the up position, condition the specimen in a water bath at 25 for 1 hour.
Arrange the penetrometer so that the wax specimen is completely immersed in the water bath while penetration is run. Lower the needle until the tip just touches the top surface of the specimen. Release the needle for 5 seconds, and read the depth of penetration in tenths of millimeters. Perform four determinations, and calculate the average value of the four readings. The consistency value of Microcrystalline Wax is between 3 and 100 (not less than 0.3 mm and not more than 10.0 mm).
Acidity— If the addition of phenolphthalein TS in the test for Alkalinity produces no pink color, add 0.1 mL of methyl orange TS: no red or pink color is produced.
Alkalinity— Introduce 35 g into a 250-mL separator, add 100 mL of boiling water, and shake vigorously for 5 minutes. Draw off the separated water into a casserole, wash further with two 50-mL portions of boiling water, and add the washings to the casserole. To the pooled washings add 1 drop of phenolphthalein TS, and boil: the solution does not acquire a pink color.
Residue on ignition 281 Heat 2 g in an open porcelain or platinum dish over a flame: it volatilizes without emitting an acrid odor and on ignition yields not more than 0.1% of residue.
Organic acids— To 20 g add 100 mL of a mixture of neutralized alcohol and water (1 in 2), agitate thoroughly, and heat to boiling. Add 1 mL of phenolphthalein TS, and titrate rapidly with 0.1 N sodium hydroxide VS, with vigorous agitation, to a sharp pink end-point in the alcohol-water layer: not more than 0.4 mL of 0.1 N sodium hydroxide is required.
Fixed oils, fats, and rosin— Digest 10 g with 50 mL of sodium hydroxide solution (1 in 5) at 100 for 30 minutes. Separate the water layer, and acidify it with 2 N sulfuric acid: no oily or solid matter separates.
Residual solvents 467: meets the requirements.
(Official January 1, 2007)
Auxiliary Information— Staff Liaison : Hong Wang, Ph.D. , Senior Scientific Associate
Expert Committee : (EM205) Excipient Monographs 2
USP29–NF24 Page 3458
Phone Number : 1-301-816-8351