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A validated, simple, and sensitive fluorescence quenching method for the determination of ranitidine, nizatidine, and cimetidine in tablets and biological fluids is presented. This is the first single fluorescence method reported for the analysis of all three H(2) antagonists. The competitive reaction between the investigated drug and the palmatine probe for the occupancy of the cucurbit[7]uril (CB[7]) cavity was studied using spectrofluorometry. CB[7] was found to react with the probe to form a stable complex. The fluorescence intensity of the complex was also enhanced greatly. However, the addition of the drug dramatically quenched the fluorescence intensity of the complex. Accordingly, a new fluorescence quenching method for the determination of the studied drugs was established. The different experimental parameters affecting the fluorescence quenching intensity were studied carefully. At optimum reaction conditions, the rectilinear calibration graphs between the fluorescence quenching values (ΔF) and the medicament concentration were obtained in the concentration range of 0.04-1.9 μg mL(-1) for the investigated drugs. The limits of detection ranged from 0.013 to 0.030 μg mL(-1) at 495 nm using an excitation wavelength of 343 nm. The proposed method can be used for the determination of the three H(2) antagonists in raw materials, dosage forms and biological fluids.

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