Solvent— Prepare a mixture of dichloromethane and methanol (1:1).

Standard solutions— Dissolve an accurately weighed quantity of USP Omeprazole RS in Solvent, and mix to obtain Standard solution A having a known concentration of about 0.5 mg per mL. Dilute this solution quantitatively with Solvent to obtain Standard solution B and Standard solution C having known concentrations of about 0.15 mg per mL and 0.05 mg per mL, respectively.

Test solution— Prepare a solution of Omeprazole in Solvent containing 50 mg per mL.

Identification solution— Dilute a volume of the Test solution quantitatively with Solvent to obtain a solution containing 0.25 mg per mL.

Procedure— Separately apply 10 µL of the Test solution, the Identification solution, and each of the Standard solutions to a thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of a mixture of ammonia-saturated dichloromethane, dichloromethane, and isopropyl alcohol (2:2:1) until the solvent front has moved about three-fourths of the length of the plate. [note—Prepare ammonia-saturated dichloromethane as follows. Shake 100 mL of dichloromethane with 30 mL of ammonium hydroxide in a separatory funnel, allow the layers to separate, and use the lower layer.] Remove the plate from the developing chamber, mark the solvent front, allow the solvent to evaporate, and examine the plate under short-wavelength UV light: the chromatograms show principal spots at about the same RF value. Estimate the intensities of any secondary spots observed in the chromatogram of the Test solution by comparison with the spots in the chromatograms of the Standard solutions: no secondary spot from the chromatogram of the Test solution is larger or more intense than the principal spot obtained from Standard solution B (0.3%), and the sum of the intensities of all secondary spots obtained from the Test solution is not more intense than the principal spot obtained from Standard solution A (1.0%).

Diluent— Use Mobile phase.

Phosphate buffer, Mobile phase, System suitability solution, and Chromatographic system— Proceed as directed in the Assay.

Test solution— Dissolve an accurately weighed quantity of Omeprazole in Diluent to obtain a solution containing about 0.16 mg per mL. [note—Prepare this solution fresh.]

Procedure— Inject equal volumes (about 40 µL) of the Test solution and Diluent into the chromatograph, and allow the Test solution to elute for not less than two times the retention time of omeprazole. Record the chromatograms, and measure the peak responses. Calculate the percentage of each impurity in the portion of Omeprazole taken by the formula: in which ri is the peak response for each impurity, and rs is the sum of the responses of all of the peaks: not more than 0.3% of any individual impurity is found, and the sum of all impurities is not more than 1.0%.

500C(rU / rS)