New sensitive kinetic spectrophotometric methods for determination of omeprazole in dosage forms

Abstract

New rapid, sensitive, and accurate kinetic spectrophotometric methods were developed, for the first time, to determine omeprazole (OMZ) in its dosage forms. The methods were based on the formation of charge-transfer complexes with both iodine and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The variables that affected the reactions were carefully studied and optimized. The formed complexes and the site of interaction were examined by UV/VIS, IR, and (1)H-NMR techniques, and computational molecular modeling. Under optimum conditions, the stoichiometry of the reactions between OMZ and the acceptors was found to be 1 : 1. The order of the reactions and the specific rate constants were determined. The thermodynamics of the complexes were computed and the mechanism of the reactions was postulated. The initial rate and fixed time methods were utilized for the determination of OMZ concentrations. The linear ranges for the proposed methods were 0.10-3.00 and 0.50-25.00 mug mL(-1) with the lowest LOD of 0.03 and 0.14 mug mL(-1) for iodine and DDQ, respectively. Analytical performance of the methods was statistically validated; RSD was <1.25% for the precision and <1.95% for the accuracy. The proposed methods were successfully applied to the analysis of OMZ in its dosage forms; the recovery was 98.91-100.32% +/- 0.94-1.84, and was found to be comparable with that of reference method.

Figure 1

Absorption spectra of OMZ (1), iodine, 0.20 mg mL⁻¹ in 1,2-dichloroethane (2), DDQ, 0.40 mg mL⁻¹ in acetonitrile (3), OMZ-iodine complex in 1,2-dichloroethane at 25 ± 2°C (4), and OMZ-DDQ complex in acetonitrile at 25 ± 2°C (5). Concentrations of OMZ were 30.00, 1.50, and 20.00 μg mL⁻¹ for the absorption spectra numbers (1), (4), and (5), respectively.

Scheme 1

Scheme 2

Figure 2

Absorption spectra of OMZ-DDQ complex as a function of time. The complex was generated by carrying out the reaction of OMZ (20.00 μg mL⁻¹) with DDQ (0.40 μg mL⁻¹) in acetonitrile at 25 ± 2°C.

Figure 3

The absorbance-time curve for the reaction of OMZ at 25 ± 2°C with (a) iodine (0.20 mg mL⁻¹) at 362 nm; the concentrations of OMZ were 1.45 × 10⁻⁶ (⋄), 2.90 × 10⁻⁶ (◆), 4.35 × 10⁻⁶ (∆), 5.80 × 10⁻⁶ (▴), 7.25 × 10⁻⁶ (°), and 8.70 × 10⁻⁶ M (●), and (b) DDQ (0.40 mg mL⁻¹) at 418 nm; the concentrations of OMZ were 0.73 × 10⁻⁵ (●), 1.45 × 10⁻⁵ (°), 2.90 × 10⁻⁵ (▴), 5.80 × 10⁻⁵ (∆), 8.70 × 10⁻⁵ (◆), and 1.15 × 10⁻⁴ M (⋄).

Scheme 3

Figure 4

The most energy-minimized conformation of OMZ-DDQ charge-transfer complex.