A: Transfer a volume of Injection, equivalent to about 15 mg of lactic acid, to a 50-mL conical flask, add 1 mL of 2 N sulfuric acid, and mix. Add, dropwise, potassium permanganate solution (3.2 in 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 250 mg of sodium nitroferricyanide in water to make 9 mL of solution, adding 1 mL of 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 50 mg of USP Pentazocine RS in 25 mL of 0.01 N hydrochloric acid in a separator, and use this in place of the Standard solution specified under Identification—Organic Nitrogenous Bases 181: a volume of Injection, equivalent to about 50 mg of pentazocine, meets the requirements of the test.

(Official January 1, 2007)

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 25 mm with a styrene-divinylbenzene cation-exchange resin that has been previously soaked in 3 N hydrochloric acid for not less than 2 hours. Pass 10 mL of methanol through the column followed by 50 mL of 3 N hydrochloric 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 60 mg of USP Pentazocine RS, accurately weighed, to a 50-mL volumetric flask, dilute with a mixture of equal volumes of methanol and 6 N hydrochloric acid to volume, and mix. Transfer 10.0 mL of this solution to a 100-mL volumetric flask, dilute with the mixture of methanol and 6 N hydrochloric acid to volume, and mix. The concentration of USP Pentazocine RS in the Standard preparation is about 120 µg per mL.

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

Procedure— Concomitantly determine the absorbances of the Assay preparation and the Standard preparation in 1-cm cells at the wavelength of maximum absorbance at about 278 nm, with a suitable spectrophotometer, using a mixture of equal volumes of methanol and 6 N hydrochloric acid as the blank. Calculate the quantity, in mg, of pentazocine (C19H27NO) in each mL of the Injection taken by the formula: in which C is the concentration, in µg per mL, of USP Pentazocine RS in the Standard preparation; V is the volume, in mL, of Injection taken; and AU and AS are the absorbances of the Assay preparation and the Standard preparation, respectively.