Diluent, Mobile phase, System suitability preparation, and Chromatographic system— Proceed as directed in the Assay.

Standard solution— Transfer about 20 mg of USP Pantoprazole Sodium RS, accurately weighed, to a 50-mL volumetric flask, dissolve in 5 to 10 mL of a mixture of acetonitrile and water (1:1), and dilute with Diluent to volume. Further dilute with Diluent quantitatively, and stepwise if necessary, to obtain a solution having a known concentration of about 0.0004 mg per mL.

Test solution— Transfer about 20 mg of Pantoprazole Sodium, accurately weighed, to a 50-mL volumetric flask, dissolve in 5 to 10 mL of a mixture of acetonitrile and water (1:1), dilute with Diluent to volume, and mix.

Chromatographic system (see Chromatography 621)—Prepare as directed in the Assay. Chromatograph the System suitability preparation, and record the peak responses as directed for Procedure. Identify the components on the basis of their relative retention times (Table 1): the resolution, R, between the pantoprazole related compound A and pantoprazole peaks is not less than 10.0.

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 peak responses. Calculate the percentage of each impurity in the portion of Pantoprazole Sodium taken by the formula: in which CS and CT are the concentrations, in mg per mL, of pantoprazole sodium in the Standard solution and the Test solution, respectively; ri is the peak response of each impurity obtained from the Test solution; and rS is the pantoprazole peak response obtained from the Standard solution. The reporting level for impurities is 0.05%.

Diluent— Prepare a mixture of acetonitrile and 0.001 N sodium hydroxide solution (50:50).

Standard solution— Dissolve an accurately weighed quantity of USP Pantoprazole Sodium RS in Diluent, and dilute quantitatively to obtain a solution having a known concentration of about 0.03 mg per mL.

Test solution— Prepare a solution of Pantoprazole Sodium in Diluent having a known concentration of about 0.46 mg per mL.

System suitability solution— Dissolve suitable amounts of USP Pantoprazole Sodium RS, USP Pantoprazole Related Compound A RS, USP Pantoprazole Related Compound B RS, USP Pantoprazole Related Compound C RS, USP Pantoprazole Related Compound D and F Mixture RS, and USP Pantoprazole Related Compound E RS in Diluent to obtain a solution containing about 0.46 mg of pantoprazole sodium per mL and about 1.3 µg each of related compounds A, B, C, and E per mL, and about 1.3 µg of the D and F mixture per mL.

Solution A— Prepare a solution of dibasic potassium phosphate (1.74 g/L) adjusted with a solution of phosphoric acid (330 g/L) to a pH of 7.00 ± 0.05.

Solution B— Use acetonitrile.

Mobile phase— Use variable mixtures of Solution A and Solution B as directed below for Chromatographic system. Make adjustments as necessary (see System Suitability under Chromatography 621).

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with either a programmable variable wavelength detector or two separate detectors capable of monitoring at 290 nm and at 305 nm, and a 4-mm × 12.5-cm column that contains 5-µm packing L1. The column temperature is maintained at 40. The flow rate is about 1.0 mL per minute. The chromatograph is programmed as follows. Chromatograph the System suitability solution, and record the peak responses at 290 nm as directed for Procedure. Identify the components based on relative retention times (Table 2): the resolution, R, between pantoprazole related compound E and pantoprazole related compounds D and F is not less than 1.5. Chromatograph the Standard solution at 290 nm, and record the peak responses as directed for Procedure: the tailing factor is not more than 2; and the relative standard deviation for replicate injections is not more than 5.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms at 290 nm and 305 nm, and measure the responses for the major peaks. [Note—Pantoprazole related compound C is monitored using a wavelength of 305 nm, and all other compounds are monitored at 290 nm.] Calculate the percentage of each impurity in the portion of Pantoprazole Sodium taken by the formula: in which CS is the concentration, in mg per mL, of pantoprazole sodium in the Standard solution; CU is the concentration, in mg per mL of Pantoprazole Sodium in the Test solution; F is the response factor of an individual pantoprazole related compound relative to the response of pantoprazole sodium (Table 2); ri is the peak response of each impurity obtained from the Test solution; and rS is the pantoprazole peak response obtained from the Standard solution. The reporting level for impurities is 0.05%.

Time (minutes)	Solution A (%)	Solution B (%)	Elution
0–10	86	14	isocratic
10–35	86®42	14®58	linear gradient
35–36	42®86	58®14	linear gradient
36–46	86	14	re-equilibration

100(CS / CU)(rU / r S)