Medium: pH 6.8 phosphate buffer (see Buffer Solutions in the section Reagents, Indicators, and Solutions); 1000 mL.

Apparatus 1: 100 rpm.

Time: 30 minutes.

Procedure— Determine the amount of C17H21NO3 dissolved by employing UV absorption at the wavelength of maximum absorbance at about 274 nm on filtered portions of the solution under test, suitably diluted with Dissolution Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Etodolac RS in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C17H21NO3 is dissolved in 30 minutes.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile, water, and phosphoric acid (500:500:0.25). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Etodolac RS in Mobile phase to obtain a solution having a known concentration of about 0.2 mg per mL. Prepare this solution fresh daily.

System suitability solution— Dissolve suitable quantities of USP Etodolac Related Compound A RS and USP Etodolac RS in Mobile phase to obtain a solution containing about 0.01 mg of etodolac related compound A and 0.2 mg of etodolac per mL.

Assay preparation— Weigh not fewer than 20 Capsules, and transfer the contents as completely as possible to a suitable container. Remove any residual powder from the empty capsules with the aid of a current of air, and weigh the capsule shells, determining the weight of the contents by difference. Mix the contents of the Capsules, and transfer an accurately weighed portion of the powder, equivalent to about 1000 mg of etodolac, to a 500-mL volumetric flask, add 300 mL of Mobile phase, shake for 15 minutes, sonicate for 5 minutes, cool, dilute with Mobile phase to volume, and mix. Allow to settle for 10 minutes. Pipet 10.0 mL of the solution to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix. Pass the solution through a filter having a 0.45-µm or finer porosity, prior to use.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 274-nm detector and a 4.6-mm × 25-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.8 for etodolac related compound A and 1.0 for etodolac; the resolution, R, between etodolac related compound A and etodolac is not less than 2; the tailing factor is not more than 2; and the relative standard deviation for replicate injections is not more than 2%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of etodolac (C17 H21NO3) in the portion of Capsule contents taken by the formula: in which C is the concentration, in mg per mL, of USP Etodolac RS in the Standard preparation; and rU and rS are the etodolac peak responses obtained from the Assay preparation and the Standard preparation, respectively.