Chemicals and drug. All other chemicals were p. The stock solution was prepared in methanol:NaOH 2.
Chiral Selectors in Capillary Electrophoresis: Trends during –
Chiral separation optimization. HPLC analysis. When the columns were not in use, the mobile phases were replaced with the storage solvent recommended by the column suppliers.
CE analysis. The plain buffer solutions were prepared in water purified with a MilliQ-plus system Millipore Co. The solutions were then sonicated for 5 min and filtered through 0. New capillaries were conditioned by rinsing with NaOH 1.
Before each analysis the capillary was washed with NaOH 0. Sample preparation and analysis. Ten tablets of commercially available samples containing 20 mg of racemic omeprazole or 40 mg of S -omeprazole were accurately weighed, ground and homogenized. An amount of 50 mg was transferred to a 50 mL volumetric flask. After the addition of approximately 40 mL methanol:NaOH 2. An aliquot was filtered through 0.
Methods of validation. Each standard solution was analyzed in duplicate and plots of peak height versus omeprazole enantiomer concentrations were constructed. Linear regression lines were used for determination of enantiomer concentration in the samples. The precision and accuracy of the method were evaluated by determining omeprazole enantiomers in a tablet sample containing 10 mg of each enantiomer. Ten tablets were weighted, powdered and homogenized. Between day experiments were carried out by analyzing aliquots of this sample for 5 days.
Results and Discussion.
Quantitative applications of the resolution of enantiomers by capillary electrophoresis
Polysaccharide based stationary phases together with the chemically bound protein phases have proved to be the most useful stationary phases for the resolution of chiral drugs by high-performance liquid chromatography. In the present study, these columns were evaluated for the resolution of omeprazole and some selected separation and chromatographic conditions are shown in Figure 2. Among the chiral columns evaluated, only Chiralcel OJ-R did not show complete resolution of omeprazole. The Chiralpak AD column was selected for development of the method due to its stability and high resolving ability.
Among the several chiral selectors reported in the literature for CE enantioselective analysis of drugs, cyclodextrins CD and their derivatives are the most widely used due to their high enantioselectivity. The resolution of neutral compounds is possible by using charged CD derivatives. One of the most successful charged CD is sulfated b -CD, whose mobility is opposite to the electroosmotic flow showing high strong resolving power even at very low concentrations. The complete resolution of omeprazole was only obtained using sulfated b -CD Figure 3. The elution order established by the injection of the pure S -enantiomer was the same for both methods, i.
Sample preparation was carried out by dissolving omeprazole from the tablets using a methanol:NaOH 2. Figure 4 and 5 respectively show the chromatograms and eletropherograms obtained for the analysis of commercially available samples of rac-omeprazole and S -omeprazole. The precision and accuracy experiments were carried out using a commercially available sample of rac-omeprazole and the results are shown in Table 1.
Both methods show accuracy and precision of the order of a few percent.
Detection limits and quantitation limits also reported on Table 1 show that the HPLC method is more sensitive. This is not a problem for drug assay since the amount of sample is not a limiting factor. The present results confirm that the proposed chiral HPLC and CE methods were well suited for the enantioselective analysis of omeprazole in pharmaceutical formulations.
Chiral CE is more versatile and less expensive than HPLC using chiral columns, since several expensive columns are required to cover a reasonably wide application range and column lifetime tends to be relatively short. In addition, chiral HPLC requires a large volume of organic solvents. On the other hand, the HPLC method is more sensitive and resulted in a better resolution of omeprazole enantiomers.
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