A flow-injection chemiluminescence (CL) method is described for the determination of ciprofloxacin (CIP), norfloxacin (NOR) and ofloxacin (OFL), commonly used antibiotics of the fluoroquinolones family. The method is based on the CL reaction of the fluoroquinolones with tris(2,2'-bipyridyl) ruthenium(II) and Ce (IV), in sulfuric acid medium. The maximum CL emission, given at 0.45 min for CIP, at 0.35 min for NOR and at 0.04 min for OFL, respectively, were measured, allowing the simple application of the proposed method to the routine analysis of the antibiotics. The methods were applied to the determination of CIP, NOR and OFL, in several pharmaceutical preparations, with very satisfactory results, and validated by a previously reported HPLC method. The time-resolved equipment allowed the measurement of the kinetic evolution of the chemiluminescence signals. In base to the differences in the kinetic behaviour of ofloxacin with respect to ciprofloxacin and norfloxacin, binary mixtures of the drugs were resolved by using the time-resolved chemiluminescence signals, in combination with first-order partial least-squares (PLS) multivariate calibration.
The determination of paracetamol and salicylamide in the presence of each other was performed by means of a first-derivative spectrofluorimetric method with a "zero-crossing'' technique of measurement. The reported method is based on the oxidation of the paracetamol with potassium hexacyanoferrate (111) to give a fluorescent substance.The quantitative ranges are 80-640 pg 1. ' for paracetamol and 3.2-150.4 pg I-I for salicylamide, with relative standard deviations of 3.1 and 1.3 pg 1-I, respectively. Good results, both in terms of sensitivity and reproducibility, were obtained in the determination of paracetamol and salicylamide in the presence of each other by using this technique. The method was applied to several pharmaceutical formulations containing the drugs and was found to be satisfactory.
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