A: Transfer a volume of Injection,equivalent to about 15mg of lactic acid,to a 50-mLconical flask,add 1mLof 2Nsulfuric acid,and mix.Add,dropwise,potassium permanganate solution (3.2in 100),until a slight excess has been added,as evidenced by a violet color.[NOTE—The addition of a large excess of potassium permanganate may result in a false negative test for lactate.]Moisten a piece of filter paper with a color-indicating solution (previously prepared by dissolving 250mg of sodium nitroferricyanide in water to make 9mLof solution,adding 1mLof morpholine,and mixing).Place the moistened filter paper over the conical flask opening,and heat the solution moderately:the acetaldehyde fumes produced turn the moistened filter paper blue.

B: Dissolve 50mg of USP Pentazocine RSin 25mLof 0.01Nhydrochloric acid in a separator,and use this in place of the Standard solution specified under Identification—Organic Nitrogenous Bases á181ñ:a volume of Injection,equivalent to about 50mg of pentazocine,meets the requirements of the test.

Ion-exchange column— Place a pledget of glass wool in the base of a 6-mm (ID)tube equipped with a stopcock,and fill the tube to a height of about 25mm with a styrene-divinylbenzene cation-exchange resin that has been previously soaked in 3Nhydrochloric acid for not less than 2hours.Pass 10mLof methanol through the column followed by 50mLof 3Nhydrochloric acid,then wash the column with water until the eluate is neutral.[Caution—Do not permit the column to become dry at anytime.]

Standard preparation— Transfer about 60mg of USP Pentazocine RS,accurately weighed,to a 50-mLvolumetric flask,dilute with a mixture of equal volumes of methanol and 6Nhydrochloric acid to volume,and mix.Transfer 10.0mLof this solution to a 100-mLvolumetric flask,dilute with the methanol-6Nhydrochloric acid mixture to volume,and mix.The concentration of USP Pentazocine RSin the Standard preparationis about 120µg per mL.

Assay preparation— Dilute an accurately measured volume of Injection,equivalent to about 60mg of pentazocine,with water to 10.0mL,and mix.Transfer 2.0mLof this solution to the column,then pass 100mLof water through the column at a rate of about 2mLper minute,and discard the eluate.Place a 100-mLvolumetric flask under the column,and pass through the column a mixture of equal volumes of methanol and 6Nhydrochloric acid until approximately 95mLof eluate has been collected.Remove the flask,dilute with the methanol-6Nhydrochloric acid mixture to volume,and mix.

Procedure— Concomitantly determine the absorbances of the Assay preparationand the Standard preparationin 1-cm cells at the wavelength of maximum absorbance at about 278nm,with a suitable spectrophotometer,using a mixture of equal volumes of methanol and 6Nhydrochloric acid as the blank.Calculate the quantity,in mg,of pentazocine (C19H27NO)in each mLof the Injection taken by the formula: in which Cis the concentration,in µg per mL,of USP Pentazocine RSin the Standard preparation;Vis the volume,in mL,of Injection taken;and AUand ASare the absorbances of the Assay preparationand the Standard preparation,respectively.