A: Infrared Absorption 197K.

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

C: Differential scanning calorimetry 891—Accurately weigh 2 to 6 mg of Fexofenadine Hydrochloride into an aluminum pan, and crimp the pan, using a suitable sample press. Analyze the sample from 25 to 225 at 10 per minute. The sample exhibits a single endotherm between 193 and 199. [NOTE—The pan can be sealed hermetically, provided a pinhole is punched into the lid so that the sample can degas during heating.]

Ammonium acetate buffer solution— Add 2.3 mL of glacial acetic acid to 2000 mL of water. Adjust with 6 N ammonium hydroxide to a pH of 4.0 ± 0.1.

Mobile phase— Prepare a filtered and degassed mixture of Ammonium acetate buffer solution and acetonitrile (80 : 20). Make adjustments if necessary (see System Suitability under Chromatography 621).

System suitability solution— Add about 1.2 mg of USP Fexofenadine Related Compound B RS, accurately weighed, to a 5-mL volumetric flask. Dilute with Mobile phase to volume, and mix. Transfer 2.0 mL of the solution so obtained into a 100-mL volumetric flask; add about 25 mg of USP Fexofenadine Hydrochloride RS, accurately weighed; dilute with Mobile phase to volume; and mix.

Standard solution— Dilute the System suitability solution quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 2.5 µg of USP Fexofenadine Hydrochloride RS per mL.

Test solution— Dissolve an accurately weighed quantity of Fexofenadine Hydrochloride in Mobile phase to obtain a solution having a concentration of about 0.25 mg per mL.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm × 25-cm column that contains packing L45. The column is maintained at room temperature. The flow rate is about 0.5 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the retention time for fexofenadine is between 15 and 23 minutes; the relative retention times are about 0.7 for fexofenadine related compound B and 1.0 for fexofenadine; and the resolution, R, between fexofenadine and fexofenadine related compound B is not less than 3.0.

Procedure— Separately inject equal volumes (about 20 µL) of the Test solution and the Standard solution into the chromatograph, record the chromatograms, and measure the peak areas. Calculate the percentage of fexofenadine related compound B in the portion of Fexofenadine Hydrochloride taken by the formula: in which 0.8 is the relative response factor for fexofenadine related compound B 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 for fexofenadine related compound B obtained from the Test solution; and rS is the peak response for fexofenadine obtained from the Standard solution: not more than 0.1% is found.

Phosphate–perchlorate buffer, Diluting solution, Mobile phase, and Chromatographic system— Prepare as directed in the Assay.

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

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 Test solution, the Standard solution, the Reference solution, and Mobile phase (used as the blank) into the chromatograph; record the chromatograms; and measure the peak areas, excluding the peaks corresponding to those obtained from the Mobile phase. Calculate the percentage of fexofenadine related compound A in the portion of Fexofenadine Hydrochloride 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 for 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 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; rS is the peak response of fexofenadine obtained from the Standard solution; and 1.1 is the relative response factor for the decarboxylated degradant relative to fexofenadine. Calculate the percentage of other impurities in the portion of Fexofenadine Hydrochloride taken by the formula: in which CS 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; ri is the peak response for any other impurity obtained from the Test solution; and rS is the peak response of fexofenadine obtained from the Reference solution: not more than 0.18% of fexofenadine related compound A is found, not more than 0.15% of decarboxylated degradant is found, not more than 0.1% of any other unknown impurity is found, and not more than 0.30% of total impurities is found.

Phosphate–perchlorate buffer— Dissolve 6.64 g of monobasic sodium phosphate and 0.84 g of sodium perchlorate in 1000 mL of water. Adjust with phosphoric acid to a pH of 2.0.

Diluting solution— Prepare a mixture of acetonitrile and Phosphate–perchlorate buffer (50:50).

Mobile phase— Prepare a filtered and degassed mixture of Phosphate–perchlorate buffer and acetonitrile (65:35). Add 3 mL of triethylamine per L, and mix. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Prepare a solution of USP Fexofenadine Hydrochloride RS and USP Fexofenadine Related Compound A RS in Mobile phase having known concentrations of about 0.06 mg per mL and 0.005 mg per mL, respectively.

Assay stock preparation— Transfer about 50 mg of Fexofenadine Hydrochloride, accurately weighed, to a 50-mL volumetric flask, and dissolve in and dilute with Diluting solution to volume to obtain a solution having a concentration of about 1.0 mg of fexofenadine hydrochloride per mL.

Assay preparation— Transfer 3.0 mL of the Assay stock preparation to a 50-mL volumetric flask, and dilute with Mobile phase to volume to obtain a solution having a concentration of about 0.06 mg per mL.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm × 25-cm column that contains packing L11. The column is maintained at room temperature. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between fexofenadine and fexofenadine related compound A is not less than 10; the tailing factor is not more than 2.0; and the relative standard deviations for replicate injections determined from fexofenadine and fexofenadine related compound A are not more than 2.0% and 3.0%, respectively.

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 areas for the major peaks. Calculate the quantity, in mg, of C32H39NO4·HCl in the portion of Fexofenadine Hydrochloride 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 for fexofenadine obtained from the Assay preparation and the Standard preparation, respectively. USP29