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A simple, rapid and sensitive batch and flow injection spectrophotometric methods have been developed for the determination of paracetamol in pure form and pharmaceutical preparations. The proposed methods are based on the oxidative coupling reaction of paracetamol with 4-aminoantipyrine in presence of ammonium persulfate in alkaline medium to produce an orangereddish product that having absorptivity maximum at 461 nm. The optimum reaction conditions and other analytical parameters have been evaluated. Linearity was observed from 2-16 and 100-700 g mL -1 paracetamol by batch and flow injection procedures, respectively. Statistical analysis of the results and comparison with results by the British Pharmacopoeia method are also reported.

A batch and flow injection (FI) spectrophotometric methods have been developed for the determination of phenylephrine hydrochloride (PHP) and amoxicillin trihydrate (AMOX) in pharmaceutical preparations. The methods are based on coupling reaction of 2,4dinitrophenylhydrazine (DNPH) with either PHP or AMOX in the presence of sodium hydroxide to form a red colored water-soluble products with absorption maxima at 525 and 515 nm for PHP and AMOX respectively. Optimum conditions for determining the drugs were investigated. Beer's law were obeyed over the concentration ranges of 2-50μg/ml PHP and 1-40 μg/ml AMOX for batch method, and of 30-1000 μg/ml PHP and50-1200μg/ml AMOX for FIA method. The limits of detection were 1.044 μg/ml PHP and 0.230 μg/ml AMOX for batch method, and for FI method were 14.21 μg/ml PHP and 34.00 μg/ml AMOX. The proposed methods were applied satisfactorilyto the determination of PHP and AMOX in pharmaceutical preparations. The procedures are characterized by its simplicity, accuracy and precision. The results obtained were in good agreement with those obtained using reference standard methods at the 95% confidence level.

New, simple and sensitive batch and flow injection spectrophotometric methods for the determination of doxycycline hyclate (DCH) in pharmaceutical preparations were developed. These methods were based on diazotization-coupling reaction between diazotized o-nitroanline (DONA) and DCH in sodium carbonate medium to form yellow-orange colored azo dye product has a maximum absorbance at 448 nm. Calibration graphs of absorbance versus concentration show that Beerʼs law were obeyed over the concentration ranges 0.4-52, 5-200 µg mL-1 of DCH, with limit of detection of 0.284, 1.117 µg mL-1 of DCH for batch and flow injection analysis (FIA) procedure respectively, and sample throughput was 171 h-1 for FIA method. All chemical and physical conditions affected on the developed colored product were carefully studied and the proposed methods were successfully applied for the determination of doxycycline in its pharmaceutical preparations.

A simple, rapid and sensitive spectrophotometric method for the determination of trace amounts of 4-aminoantipyrine in aqueous solution is described. The method is based on a coupling reaction between 4-aminoantipyrine and diazotised 4-nitroaniline to form an intense yellow, water-soluble dye that is stable and has a maximum absorption at 380 nm. A graph of absorbance versusconcentration shows that Beer's law is obeyed over the concentration range 25-750 pg of 4-aminoantipyrine in a final volume of 25 ml (is., 1-30 p.p.m.) with a molar absorptivity of 1.3 x 104 I mol-1 cm-1, a Sandell sensitivity of 156.4 x 10-4 pg cm-2, a relative error of -0.8 to +I .5% and a relative standard deviation of 0.3-2.0% depending on the concentration.The optimum conditions for full colour development and the interference of foreign organic compounds have been investigated. The proposed method does not require either temperature control or a solvent extraction step.

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