Determination of Fluoroquinolones in Pharmaceutical Formulations by Extractive Spectrophotometric Methods Using Ion-Pair Complex Formation with Bromothymol Blue

Abstract

In this paper, we reported a new, simple, accurate, and precise extractive spectrophotometric method for the determination of fluoroquinolones (FQs) including ciprofloxacin (CFX), levofloxacin (LFX), and ofloxacin (OFX) in pharmaceutical formulations. The proposed method is based on the ion-pair formation complexes between FQs and an anionic dye, bromothymol blue (BTB), in acidic medium. The yellow-colored complexes which were extracted into chloroform were measured at the wavelengths of 420, 415, and 418 nm for CFX, LFX, and OFX, respectively. Some effective conditions such as pH, dye concentration, shaking time, and organic solvents were also systematically studied. Very good limit of detection (LOD) of 0.084 µg/mL, 0.101 µg/mL, and 0.105 µg/mL were found for CFX, LFX, and OFX, respectively. The stoichiometry of the complexes formed between FQs and BTB determined by Job's method of continuous variation was 1 : 1. No interference was observed from common excipients occurred in pharmaceutical formulations. The proposed method has been successfully applied to determine the FQs in some pharmaceutical products. A good agreement between extractive spectrophotometric method with high-performance liquid chromatography mass spectrometry (HPLC-MS) for the determination of FQs in some real samples demonstrates that the proposed method is suitable to quantify FQs in pharmaceutical formulations.

Figure 1

Chemical structures of ciprofloxacin (a), levofloxacin (b), ofloxacin (OFX) (c), and bromothymol blue (d).

Figure 2

The effect of solvent on the ion-pair complex formation (10 µg/mL of fluoroquinolones (FQs) with bromothymol blue (BTB)).

Figure 3

Effect of pH on the absorbances of 10 μg/mL of OFX, LFX, and CFX.

Figure 4

Effect of the volume of 0.025% BTB on the absorbance of 10 μg/mL of OFX, LFX, and CFX.

Figure 5

Effect of shaking time on the ion-pair complexes.

Figure 6

Job's method of continuous variation graph for the reaction of drug with acid dyes BTB, [drug] = [dye] = 3.0 × 10⁻⁴ M.

Figure 7

Proposal mechanism for the reaction between levofloxacin, ofloxacin, and bromothymol blue.

Figure 8

Absorption spectrum of ion-associate complexes of fluoroquinolones (10 µg/mL) with BTB against reagent blank.

Figure 9

Calibration curves for OFX, LFX, and CFX at 418, 415, and 420 nm, respectively.