A simple, rapid and accurate method for the simultaneous determination of ascorbic acid, caffeine and paracetamol in drug formulations has been developed. Peak currents were measured with a glassy carbon electrode at +0.350, +0.618 and +1.425 V versus a saturated calomel electrode for ascorbic acid, paracetamol and caffeine, respectively. Perchloric acid (0.1 M) - methanol (1 + 1) was used both as a solvent and supporting electrolyte. The optimum modulation amplitude, pulse repeat time and scan rate of the polarographic analyser were found to be 50 mV, 0.5 s and 5 mV s-1, respectively and the linear calibration ranges for ascorbic acid, caffeine and paracetamol were 0-35, 0-50, and 0-55 micrograms ml-1, respectively. The relative standard deviations for 9.30 micrograms ml-1 of ascorbic acid, 8.50 micrograms ml-1 of caffeine and 7.30 micrograms ml-1 of paracetamol were 1.3, 2.5 and 0.7%, respectively. Results are reported for several commercially available drugs.
A simple and accurate spectrophotometric method is proposed for the determination of tannins in tea and beer samples based on the reduction of iron(III) to iron(II) by tannins at 80 degrees C for 20 min. The iron(II) was then reacted with 1,10-phenanthroline at pH 4.4 to form a coloured complex. Background correction could be effected by precipitating the tannins in the sample solution twice with gelatin and kaolin. Absorbance measurements were made at 540 nm and the calibration graph was linear from 0 to 5.5 micrograms ml-1 of tannic acid with a slope of 0.213 A p.p.m.-1. The precision for the determination of tannins in a tea sample containing 9.45% of tannins was 1.8%. Most of the ingredients commonly found in tea and beer samples do not interfere with the determination. Several tea and beer samples were analysed for their tannin content using the proposed method.
Background-correction methods have been developed for the determination of caffeine in beverages, coffee and tea by second-derivative ultraviolet spectrophotometry. The second derivatives of caffeine were measured at 298.6 nm. Interference from tannins in beverages and tea was minimized by treating the sample with 0.1 m o l dm-3 sodium hydroxide and by precipitating tannins with copper(ti) acetate, respectively. Coffee samples were treated with sodium hydroxide (0.25-0.75 m m o l dm-3). The calibration graphs for the three types of sample had slightly different slopes (0.00146-0.00152 A nm-2 ppm-1) and linear ranges. The precision for the determination ranged from 0.3 t o 0.9%, at the 10 pg ml-1 level of caffeine. A number of cola drinks, energy drinks, lemon tea drinks, coffee samples and tea samples were analysed.
A simple and rapid voltammetric method for the determination of salicylic acid in pharmaceutical preparations and foods has been developed. The sample was extracted using either diethyl ether or ethanoldiethyl ether and then back-extracted into 0.015 M disodium hydrogen phosphate solution. The peak current was measured using a glassy carbon electrode at 0.85 V. The working range was 0-25 p.p.m. The average recovery for ointment was 99% with a standard deviation of 5.0%. Results are reported for eight d iff e re nt p ha r maceut ica I form u I a ti o ns .
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