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

B: Infrared Absorption 197K—

Medium: water; 900 mL.

Apparatus 2: 50 rpm.

Times: 15 and 45 minutes.

Buffer solution— Dissolve 1.0 g of monobasic sodium phosphate, 0.5 g of sodium perchlorate, and 0.3 mL of phosphoric acid in 300 mL of water, and mix.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and Buffer solution (700 : 300), and mix. Make adjustments if necessary (see System Suitability under Chromatography 621).

System suitability stock solution— [NOTE—A small amount of glacial acetic acid, not to exceed 5% of the total volume, is used, if necessary, to dissolve USP Fexofenadine Related Compound A RS.] Dissolve an accurately weighed quantity of USP Fexofenadine Related Compound A RS in water to obtain a solution having a known concentration of 0.44 mg per mL.

System suitability solution— Prepare a solution of USP Fexofenadine Hydrochloride RS in System suitability stock solution containing about 0.01 mg of USP Fexofenadine Related Compound A RS and 0.06 mg of USP Fexofenadine Hydrochloride RS per mL.

Standard solution— [NOTE—A small amount of methanol, not to exceed 0.5% of the total volume, is used, if necessary, to dissolve USP Fexofenadine Hydrochloride RS.] Dissolve an accurately weighed quantity of USP Fexofenadine Hydrochloride RS in water to obtain a solution having a known concentration of 0.07 mg per mL.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm × 10-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the resolution, R, between fexofenadine and fexofenadine related compound A is not less than 2.0. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 50 µL) of the Standard solution and filtered portions of the solution under test into the chromatograph, record the chromatograms, and measure the responses for the fexofenadine peaks. Calculate the quantity of C32H39 NO4·HCl dissolved.

Tolerances— Not less than 50% (Q) of the labeled amount of C32H39NO4· HCl is dissolved in 15 minutes. Not less than 75% (Q) of the labeled amount of C32H39NO4·HCl is dissolved in 45 minutes.

Phosphate–perchlorate buffer, Diluting solution, Mobile phase, and Chromatographic system— Proceed as directed in the Assay under Fexofenadine Hydrochloride.

Standard solution— Use the Standard preparation, prepared as directed in the Assay under Fexofenadine Hydrochloride.

Reference solution— Use the Assay preparation, prepared as directed in the Assay.

Test solution— Use the Assay stock preparation, prepared as directed in the Assay.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the percentage of fexofenadine related compound A in the portion of Capsules taken by the formula: in which CS is the concentration, in mg per mL, of USP Fexofenadine Related Compound A RS in the Standard solution; CT is the concentration, in mg per mL, of fexofenadine in the Test solution; and rU and rS are the peak responses of fexofenadine related compound A obtained from the Test solution and the Standard solution, respectively. Calculate the percentage of decarboxylated degradant [(+)-4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]-butyl]-isopropylbenzene], with a relative retention time of 3.2, in the portion of Fexofenadine Hydrochloride taken by the formula: in which 1.1 is the relative response factor for the decarboxylated degradant relative to fexofenadine; CS is the concentration, in mg per mL, of USP Fexofenadine Hydrochloride RS in the Standard solution; CT is the concentration, in mg per mL, of fexofenadine in the Test solution; rU is the peak response of the decarboxylated degradant obtained from the Test solution; and rS is the peak response of fexofenadine obtained from the Standard solution. Calculate the percentage of other impurities in the portion of Fexofenadine Hydrochloride taken by the formula: in which CR is the concentration, in mg per mL, of fexofenadine in the Reference solution; CT is the concentration, in mg per mL, of fexofenadine in the Test solution; rU is the peak response for any other impurity obtained from the Test solution; and rR is the peak response of fexofenadine obtained from the Reference solution. Not more than 0.3% of fexofenadine related compound A, not more than 0.2% of decarboxylated degradant, and less than 0.1% of any other unknown impurity is found; not more than 0.2% total other unknown impurities, and not more than 0.5% of total impurities is found.

Phosphate–perchlorate buffer, Diluting solution, Mobile phase, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Fexofenadine Hydrochloride.

Assay stock preparation— Remove, as completely as possible, the contents of not fewer than 20 Capsules, mix the combined contents, and finely powder by using a mortar and pestle. Transfer a portion of the powder, equivalent to about 50 mg of fexofenadine hydrochloride, accurately weighed, to a 50-mL volumetric flask. Add 40 mL of Diluting solution, and shake by mechanical means for 60 minutes. Sonicate for about 2 minutes. Allow to cool to room temperature, dilute with Diluting solution to volume, and mix.

Assay preparation— Transfer 3.0 mL of the Assay stock preparation to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix.

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 major peaks. Calculate the quantity, in mg, of fexofenadine hydrochloride (C32H39NO4·HCl) in the portion of Capsules taken by the formula: in which C is the concentration, in mg per mL, of USP Fexofenadine Hydrochloride RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively. USP29