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 10g on a steam bath,and pour 5mLof 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 3.8mLof ferric chloride CSand 1.2mLof cobaltous chloride CSin 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 IIIá741ñ: between 54and 102.
Consistency—
Apparatus— Determine the consistency of Microcrystalline Wax by means of a penetrometer fitted with a polished metal needle weighing 2.5±0.05g and having a truncated symmetric tapered angle of 910¢±15¢.The needle is tapered,with a length of 25.4mm,and the shaft attached to the needle is 58mm in length and 3.17mm in diameter.The plunger that fits into the penetrometer and guides the path of the needle weighs 47.5±0.05g.An additional weight of 50±0.05g is added to the top of the plunger to give a total load of 100g.
Procedure— The wax specimen is cast in a brass cylinder open at both ends.The cylinder has an inside diameter of 25.4mm and is 31.8mm 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 17above 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 1hour 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 25for 1hour.
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 5seconds,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 3and 100(not less than 0.3mm and not more than 10.0mm).
Acidity— If the addition of phenolphthalein TSin the test for Alkalinityproduces no pink color,add 0.1mLof methyl orange TS:no red or pink color is produced.
Alkalinity— Introduce 35g into a 250-mLseparator,add 100mLof boiling water,and shake vigorously for 5minutes.Draw off the separated water into a casserole,wash further with two 50-mLportions of boiling water,and add the washings to the casserole.To the pooled washings add 1drop of phenolphthalein TS,and boil:the solution does not acquire a pink color.
Residue on ignition á281ñ— Heat 2g 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 20g add 100mLof a mixture of neutralized alcohol and water (1in 2),agitate thoroughly,and heat to boiling.Add 1mLof phenolphthalein TS,and titrate rapidly with 0.1Nsodium hydroxide VS,with vigorous agitation,to a sharp pink end-point in the alcohol-water layer:not more than 0.4mLof 0.1Nsodium hydroxide is required.
Fixed oils,fats,and rosin— Digest 10g with 50mLof sodium hydroxide solution (1in 5)at 100for 30minutes.Separate the water layer,and acidify it with 2Nsulfuric acid:no oily or solid matter separates.
Auxiliary Information— Staff Liaison:Karen A Russo,Ph.D.,Scientist
Expert Committee:(EMC)Excipients:Monograph Content
USP28–NF23Page 3107
Phone Number:1-301-816-8379