Poloxalene, chemical structure, molecular formula, Reference Standards

Poloxalene

Oxirane,methyl-,polymer with oxirane.
Polyethylene-polypropylene glycol [9003-11-6].

»Poloxalene is a synthetic block copolymer of ethylene oxide and propylene oxide.It contains not less than 98.0percent and not more than 103.0percent of poloxalene.

Packaging and storage— Preserve in tight containers,protected from light.Store in a cool place.

USP Reference standards á11ñ— USP Poloxalene RS.

Labeling— Label it to indicate that it is for veterinary use only.

Identification—

Color reagent— Dissolve 12.7g of ammonium thiocyanate and 2.0g of cobalt nitrate in 100mLof water.

Procedure— Add 10mLof ethylene chloride to 0.5g of Poloxalene,and shake for 1minute.Add 1mLof Color reagent,and shake for 1minute:a blue color is produced in the lower layer.

Average molecular weight—

Phthalic anhydride-pyridine solution— Prepare as directed in the test for Average molecular weightunder Poloxamer.

Procedure— Using about 12g of Poloxalene,accurately weighed,proceed as directed for Procedurein the test for Average molecular weightunder Poloxamer:the average molecular weight is between 2850and 3150.

pHá791ñ: between 5.0and 7.5,in a solution (1in 40).

Water,Method Ia á921ñ: not more than 0.4%.

Hydroxyl value á401ñ—

Esterification reagent— Dissolve 166g of phthalic anhydride and 28g of imidazole in 1000mLof pyridine,and allow to stand for 2hours before using.Store in a light-resistant bottle.

Procedure— Transfer a quantity of Poloxalene,determined by dividing 420by the expected hydroxyl value and accurately weighed,to a glass-stoppered,250-mLconical flask,and add 25.0mLof Esterification reagent.Transfer 25.0mLof Esterification reagentto a second glass-stoppered,250-mLconical flask to provide the reagent blank.Add glass beads to the flasks,swirl to dissolve the Poloxalene,and fit both flasks with glass-jointed reflux condensers previously rinsed with 10mLof pyridine,and heat on a steam bath for 15minutes.Add 10mLof pyridine through each condenser,insert the stoppers,and cool under running water for 1minute.After removing the condensers,add 10mLof water and 1mLof phenolphthalein TS,and titrate with 0.5Nsodium hydroxide VSto a light pink endpoint that persists for at least 15seconds.Calculate the hydroxyl value by the formula:

(56.11N/W)(B–U),

in which Nis the normality of the 0.5Nsodium hydroxide titrant;Wis the weight,in g,of the Poloxalene taken;Band Uare the volumes,in mL,of 0.5Nsodium hydroxide consumed by the reagent blank and the solution of Poloxalene,respectively.[NOTE—If Bminus Uis greater than 10mL,repeat the test using a smaller sample.]The hydroxyl value is between 36.0and 40.0.

Cloud point— Add 10g of Poloxalene to 190.0mLof water in a 250-mLbeaker.Add a magnetic stirring bar,place on a stirrer and hot plate,and stir until dissolution is complete.Place a probe from an electronic thermometer with an accuracy of 0.2

in the solution within 3mm of the stirring bar.Continue stirring at a rate that minimizes the formation of bubbles.Adjust the hot plate so that the temperature of the solution increases at a rate of about 1

per minute.Continue to view the solution,and record the temperature when the probe can no longer be seen.This occurs between 42.5

and 46.5

Assay—

Standard preparation— Dissolve an accurately weighed quantity of USP Poloxalene RSin ethylene dichloride to obtain a solution having a known concentration of about 0.1575mg per mL.

Assay preparation— Transfer about 105mg of Poloxalene,accurately weighed,to a 100-mLvolumetric flask,add about 85mLof ethylene dichloride,and swirl to dissolve.Dilute with ethylene dichloride to volume,and mix.Transfer 15.0mLof this solution to a second 100-mLvolumetric flask,dilute with ethylene dichloride to volume,and mix.

Procedure— Transfer 10.0mLof the Standard preparation,the Assay preparation,and ethylene dichloride (to serve as a blank)to glass-stoppered tubes,add 4.0mLof the Color reagentspecified in the Identificationtest,shake vigorously for 3minutes,and then centrifuge for 5minutes.Carefully remove the lower ethylene dichloride layers from the three tubes,and using the ethylene dichloride layer from the tube containing the blank to zero the spectrophotometer,determine the UVabsorbance at 630nm of the solutions from the Standard preparationand the Assay preparation.Calculate the percentage of poloxalene in the portion of Poloxalene taken by the formula:

100(AU/AS)(CS/CU),

in which AUand ASare the absorbances of the solutions from the Assay preparationand the Standard preparation,respectively;and CSand CUare the concentrations,in mg per mL,of the Standard preparationand the Assay preparation,respectively.

Auxiliary Information— Staff Liaison:Ian DeVeau,Ph.D.,Senior Scientist

Expert Committee:(VET)Veterinary Drugs

USP28–NF23Page 1573

Pharmacopeial Forum:Volume No.29(2)Page 429

Phone Number:1-301-816-8178