A: Infrared Absorption 197K—

Test specimen— Grind at least 4 Tablets into a fine powder. Use an amount of powder equivalent to about 100 mg of flavoxate hydrochloride. Add 30 mL of methanol, and stir for about 10 minutes. Pass through a Whatman #1 filter paper, and collect the filtrate. Evaporate the methanol to dryness on a steam bath with the help of nitrogen gas. Dry the residue in vacuum at 60 for about 30 minutes. Mix 1 to 2 mg of dried residue with 200 mg of potassium bromide, and grind thoroughly for 10 to 15 minutes.

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

Mobile phase— Prepare as directed in the Assay.

Standard stock solution— Dissolve an accurately weighed quantity of USP Flavoxate Hydrochloride RS in Mobile phase, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.1 mg per mL.

USP Flavoxate Related Compound A RS stock solution— Dissolve an accurately weighed quantity of USP Flavoxate Related Compound A RS in acetonitrile to obtain a solution having a known concentration of about 0.3 mg per mL.

Standard solution— Quantitatively dilute suitable volumes of Standard stock solution and USP Flavoxate Related Compound A RS stock solution with Mobile phase to obtain a solution having a final known concentration of about 0.001 mg per mL of flavoxate hydrochloride and about 0.003 mg per mL of flavoxate related compound A.

Test solution— Filter the Assay stock preparation, prepared as directed in the Assay, through a 0.45-µm filter (polyvinylidene fluoride [PVDF] or equivalent). Use the filtrate.

Chromatographic system (see Chromatography 621)— Prepare as directed in the Assay. Chromatograph the Standard solution, and record the peak areas as directed for Procedure: the resolution, R, between flavoxate hydrochloride and flavoxate hydrochloride related compound A is not less than 10.0; the column efficiency is not less than 3000 plate counts; the tailing factor is not more than 2.0 for flavoxate hydrochloride; and the relative standard deviation for five replicate injections is not more than 2.0% for both peaks.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard solution and the Test solution into the chromatograph, and record the chromatograms. Measure the peak areas of all the peaks in the Test solution. Identify the peaks using the relative retention times as given in Table 1.

Mobile phase— Dissolve 1.0 g of sodium hexanesulfonate, 1.0 mL of triethylamine, and 1.0 mL of phosphoric acid in 650 mL of water. Filter and degas. To the filtrate, add 350 mL of acetonitrile. Mix well. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Flavoxate Hydrochloride RS, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.05 mg per mL.

Assay stock preparation— Weigh and finely powder not fewer than 20 Tablets. Weigh accurately a portion of the powder, equivalent to about 100 mg of flavoxate hydrochloride based on label claim, and transfer to a 100-mL volumetric flask. Add about 80% volume of Mobile phase. Sonicate for 10 minutes, and stir for 15 minutes. Dilute with Mobile phase to volume.

Assay preparation— Dilute the Assay stock preparation quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution with a nominal concentration of about 0.05 mg per mL of flavoxate hydrochloride, based on label claim. Filter the solution through a 0.45-µm filter (polyvinylidene fluoride [PVDF] or equivalent). Use the filtrate.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 293-nm detector and a 4.6-mm × 15-cm column that contains 5-µm packing L1. The flow rate is about 1.0 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 3000; the tailing factor is not more than 2.0; and the relative standard deviation for five replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the flavoxate hydrochloride peak whose retention time is about 4.0 minutes. Calculate the percentage of the label claim of flavoxate hydrochloride (C24H25NO4·HCl) in the portion of the Tablets taken by the formula: in which CS is the concentration, in mg per mL, of flavoxate hydrochloride in the Standard preparation; CU is the nominal concentration of flavoxate hydrochloride in the Assay preparation, based on the label claim; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.USP32