2.4. Friability test
The weight of ten tablets per sample was determined on the electronic balance. The tablets were then placed in the drum of a friabilator (Erweka GmbH, Germany) revolving at 25 r/min which exposed the tablets to rolling and repeated shock resulting from free fall within the apparatus. After 4 min, the tablets were removed from the friabilator and dusted and reweighed. The weight loss was obtained from the differences between the initial weight and final weight. The friability was calculated as the percentage weight loss.
2.5. Melting point
A tablet randomly selected from each brand was used for the determination. The ibuprofen tablet was crushed to powder using a mortar and pestle. The powder was added in 200 mL of n-hexane. The mixture was heated for 10 min with continuous stirring. The cooled mixture was filtered through a Whattman filter paper (No.1) and the filtrate evaporated to dryness in a hot water bath to give ibuprofen crystals.
The crystals were packed into a capillary tube and tapped on a hard surface to form a column at the bottom of the capillary tube. The tube was inserted into a heating block of a Gallenkamp melting point apparatus and already maintained at a temperature of 70 °C. The temperature of the heating block was raised at 0.5 °C per min until the sample melts. The melting temperature was recorded as the melting point. Triple determinations were carried out in per brand.
2.6. Disintegration time
The disintegration times of six tablets per brand were determined in distilled water at (37.0 ± 0.5) °C using the British Pharmacopoeia (BP) disintegration tester (Mk IV, Manesty Machines, UK). The apparatus is an assembly of tubes covered at the lower end with a No. 10 mesh of 2 mm diameter and opened at the upper end. The whole assembly of tubes is then immersed inside a 1 L beaker containing 900 mL of distilled water. The beaker was placed inside the water bath and maintained at a constant temperature of (37.0 ± 0.5) °C. The tubes were made to oscillate at a constant rate, that at the upward stroke about 2.5 mL of the tubes were immersed in the medium and at the downward stroke, the tube went deep inside the medium leaving about 2.5 mL portion of the tube. The time taken for all the 6 tablets to break up into granules that were able to pass through the mesh was noted as the disintegration time. The test was repeated to obtain the average disintegration time. The SD were calculated.
2.7. Dissolution rate
Dissolution test was carried out on the tablets using the United States Pharmacopeia (USP) dissolution apparatus II (paddle method) (Dissolution Tester DIS 6000, Copley Scientific, UK). A dissolution medium of 900 mL of phosphate buffer pH 7.2 maintained at (37.0 ± 0.5) °C with a basket revolution of 50 r/min was used. A 5 mL aliquots was withdrawn at various intervals and replaced with an equivalent volume maintained at same temperature (37.0 ± 0.5) °C of the dissolution medium. The samples were diluted with an equal volume of phosphate buffer. This was continued for 60 min. The absorbances of the resulting solutions were measured spectrophotometrically at λmax of 221 nm (CE 7500, Cecil Instruments Ltd). The concentration and the percentage of drug released at each time interval was determined using the equation from the standard calibration plot obtained from the pure ibuprofen. A minimum of triplicate determinations were carried out for each brand and the results were reported as mean ± SD.
2.8. Content of active UV assay
2.8.1. Standard preparation
A total of 10 μg/mL standard solution was prepared by dissolving 100 mg of ibuprofen powder in a 100 mL volumetric flask with 0.1 mol/L NaOH solution and making up to volume. A 1 mL aliquot of the solution was further diluted to 100 mL to give the desired concentration. The absorbance of the resulting solution was read at 221 nm.
2.8.2. Sample preparation
The average tablet weight of 20 tablets from each brand was gotten. The tablets were crushed into powders using a tablet miller (IKA tablet miller). Powder quantity equivalent to 100 mg ibuprofen was dissolved in a 100 mL volumetric flask with 0.1 mol/L NaOH solution and made up to volume. The solution was filtered with a Whattman filter paper (No. 1) and 1 mL aliquot of the solution was further diluted to 100 mL to give a 10 μg/mL solution. The absorbance of the resulting solution was read at 221 nm and the percentage content was calculated.
2.9. HPLC assay
The HPLC system (Agilent Infinity 1260, Agilent Technologies Inc., USA) has four gradient pumps incorporated with a solvent degasser, injector, column oven and a diode array detector. An Agilent ZORBAX Eclipse Plus C18 100 mm × 4.6 mm, 3.5 μm column was used as the stationary phase.