A: Transfer a portion of powdered Boluses, equivalent to about 500 mg of phenylbutazone, to a 250-mL conical flask, add 100 mL of solvent hexane, and heat the mixture under reflux for 15 minutes. Filter the hot mixture, and allow the filtrate to cool. Separate the crystals thus formed by filtration, and dry in vacuum at 80 for 30 minutes: the phenylbutazone so obtained responds to Identification test A under Phenylbutazone.

B: The retention time of the phenylbutazone peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

Acetate buffer, Mobile phase, Internal standard solution, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Phenylbutazone.

Assay preparation— Weigh and finely powder a Phenylbutazone Bolus. Transfer an accurately weighed portion of the powder, equivalent to about 500 mg of phenylbutazone, to a 250-mL volumetric flask. Transfer 10.0 mL of water to the flask, and shake by mechanical means for 15 minutes. Add about 120 mL of acetonitrile, and sonicate until insoluble material is dispersed into fine particles. Shake by mechanical means for 20 minutes, dilute with acetonitrile to volume, and mix. Transfer 7.0 mL of this solution to a 50-mL volumetric flask, add 10.0 mL of Internal standard solution, dilute with acetonitrile to volume, and mix. Pass a portion of this solution through a filter having a porosity of 0.5 µm or finer, discarding the first few mL of the filtrate. Use the clear filtrate as the Assay preparation. [note—Use this solution within 8 hours of its preparation.]

Procedure— Proceed as directed for Procedure in the Assay under Phenylbutazone. Calculate the quantity, in mg, of C19H20N2O2 in the portion of the Bolus taken by the formula: in which C is the concentration, in mg per mL, of USP Phenylbutazone RS in the Standard preparation, and RU and RS are the ratios of the peak responses of phenylbutazone to that of the internal standard obtained from the Assay preparation and the Standard preparation, respectively.