Chromatographic purity—
METHOD 1—
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. 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 no more intense than the principal spot obtained from
Standard solution A (1.0%).
METHOD 2—
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:
100(ri / rs),
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%.
Assay—
Phosphate buffer—
Dissolve 0.725 g of monobasic sodium phosphate and 4.472 g of anhydrous dibasic sodium phosphate in 300 mL of water, dilute with water to 1000 mL, and mix. Dilute 250 mL of this solution with water to 1000 mL. If necessary, adjust the pH with phosphoric acid to 7.6.
Mobile phase—
Prepare a filtered and degassed mixture of
Phosphate buffer and acetonitrile (3:1). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Diluent—
Prepare a mixture of 0.01 M sodium borate and acetonitrile (3:1).
Standard preparation—
Dissolve an accurately weighed quantity of
USP Omeprazole RS in
Diluent, and dilute quantitatively, and stepwise if necessary, with
Diluent to obtain a solution having a known concentration of about 0.2 mg per mL.
Assay preparation—
Transfer about 100 mg of Omeprazole, accurately weighed, to a 50-mL volumetric flask, dissolve in and dilute with Diluent to volume, and mix. Transfer 5.0 mL of this solution to a 50-mL volumetric flask, dilute with Diluent to volume, and mix.
System suitability solution—
Dilute a volume of
Standard preparation with
Diluent to obtain a solution containing about 0.1 mg of
USP Omeprazole RS per mL.
Chromatographic system (see Chromatography 621)—
The liquid chromatograph is equipped with a 280-nm detector and a 4.6-mm × 15-cm column that contains 5-µm packing L7. The flow rate is about 0.8 mL per minute. Chromatograph the
System suitability solution, and record the peak responses as directed for
Procedure: the capacity factor,
k¢, is not less than 6.0; the column efficiency is not less than 3000 theoretical plates; the tailing factor is not more than 1.5; and the relative standard deviation for replicate injections is not more than 1.0%.
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 major peaks. Calculate the quantity, in mg, of C
17H
19N
3O
3S in the portion of Omeprazole taken by the formula:
500C(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Omeprazole RS in the
Standard preparation; and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
;)
for 4 hours: it loses not more than 0.5% of its weight.