Two new simple and sensitive extraction-free spectrophotometric methods have been established for the determination of ofloxacin (OFX). The methods are based on ion-pair complex formation reaction between OFX and acidic sulphonphthalein dyes, bromocresol purple (method A), and bromocresol green (method B) in dichloromethane. The experimental variables such as reaction medium, reaction time, and reagent concentration have been carefully optimized to achieve the highest sensitivity. Both dyes react spontaneously with OFX to give yellow-colored complexes. Beer’s law is obeyed over the concentration ranges of 1.0–16？μg？ml？1 OFX with correlation coefficient of 0.999 in both methods. The molar absorptivity values are calculated to be and l？mol？1？cm？1, for method A and method B, respectively, with corresponding Sandell's sensitivity values of 0.015 and 0.019？μg cm？2. The limits of detection (LOD) and quantification (LOQ) are also reported. A Job’s plot of the absorbance versus the molar ratio of OFX to each of dyes under consideration indicated (1？:？1) ratio and the conditional stability constant ( ) of the complexes have been calculated. The proposed methods were applied successfully to the determination of OFX in tablets with good accuracy and precision and without interference from common additives. The results obtained by the proposed methods were compared favorably with those of the reference method. 1. Introduction Ofloxacin (OFX), (RS)-7-fluoro-2-methyl-6-(4-methylpiperazine-1-yl)-10-oxo-4-oxa-1-azatricyclo[7.3.1.05,13]trideca-5(13),6,8,11-tetraene-11-carboxylic acid (Figure 1), is a synthetic fluorinated quinolone derivative having activity against both gram negative and gram positive bacteria through inhibition of their DNA gyrase [1]. It is widely used in the treatment of respiratory tract and urinary tract infections [2]. OFX possesses two relevant ionizable functional groups: a basic piperazinyl group and a carboxylic group. The carboxylic group and the carbonyl groups are required for antimicrobial activity. OFX is official in the United States Pharmacopoeia [3] and the British Pharmacopoeia [4], which recommend nonaqueous titrimetry [3, 4] and HPLC [3] techniques for its assay in bulk and dosage forms. Figure 1: Chemical structure of OFX. A review of the literature revealed that several methods have been reported for the analysis of OFX in pharmaceutical preparations. HPLC has been used for the assay of OFX in pharmaceuticals when present either alone [5–7] or in combination with nitazoxanide [8]. Various other techniques including HPTLC [9],
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