Hypothesis testing for the validation of the kinetic spectrophotometric methods for the determination of lansoprazole in bulk and drug formulations via Fe(III) and Zn(II) chelates

Point and interval hypothesis tests performed to validate two simple and economical, kinetic spectrophotometric methods for the assay of lansoprazole are described. The methods are based on the formation of chelate complex of the drug with Fe(III) and Zn(II). The reaction is followed spectrophotometrically by measuring the rate of change of absorbance of coloured chelates of the drug with Fe(III) and Zn(II) at 445 and 510 nm, respectively. The stoichiometric ratio of lansoprazole to Fe(III) and Zn(II) complexes were found to be 1:1 and 2:1, respectively. The initial‐rate and fixed‐time methods are adopted for determination of drug concentrations. The calibration graphs are linear in the range 50–200 µg ml^?1 (initial‐rate method), 20–180 µg ml^?1 (fixed‐time method) for lansoprazole‐Fe(III) complex and 120–300 (initial‐rate method), and 90–210 µg ml^?1 (fixed‐time method) for lansoprazole‐Zn(II) complex. The inter‐day and intra‐day precision data showed good accuracy and precision of the proposed procedure for analysis of lansoprazole. The point and interval hypothesis tests indicate that the proposed procedures are not biased. Copyright © 2010 John Wiley & Sons, Ltd.