Analytica Chimica Acta 516 (2004) 135–140 Determination of ciprofloxacin and enoxacin in human serum samples by micellar liquid chromatography José Luis V´ ılchez, Lilia Araujo 1 , Avismelsi Prieto 2 , Alberto Navalón ∗ Research Group of Analytical Chemistry and Life Sciences, Department of Analytical Chemistry, Faculty of Sciences, University of Granada, Avda. Fuentenueva s/n, E-18071 Granada, Spain Received 7 January 2004; received in revised form 15 March 2004; accepted 15 April 2004 Available online 4 June 2004 Abstract A simple and rapid micellar liquid chromatographic (MLC) method with UV detection for the determination of ciprofloxacin and enoxacin has been developed. The separation was performed in 75 mM SDS—10 mM phosphate buffer—18 mM TBABr/3% (v/v) 1-propanol at pH 3.0. Analyses were realised using a Lichrospher 100RP 18 column (125 mm × 4 mm i.d., 5 m particle) and the operating conditions were: 0.9 ml min -1 flow rate, 25 l volume injection and detection at 281 nm. Tosufloxacin was used as an internal standard. The linear concentration range of application was 0.10–5.00 g ml -1 for both compounds, with a detection limit of 0.024 g ml -1 for ciprofloxacin and 0.025 g ml -1 for enoxacin, respectively. The analysis yielded good repeatability (RSD between 2.98 and 4.71%). The method shows recoveries for the two fluoroquinolones ranging from 93.0 to 105.4%. The proposed method was applied to human serum samples of subjects administered with these antibacterials. © 2004 Elsevier B.V. All rights reserved. Keywords: Micellar liquid chromatography; Ciprofloxacin; Enoxacin; Antibacterials; Serum analysis 1. Introduction Ciprofloxacin (CIPRO) [1-cyclopropyl-6-fluoro-1,4- dihydro-4-oxo-7-(piperazynil) quinolone-3-carboxylic acid] (Fig. 1) is a low toxicity fluoroquinolone antibiotic highly active against a broad spectrum of microbial pathogens [1,2]. Enoxacin (ENO) [1-ethyl-6-fluoro-1,4-dihydro-4- oxo-7-(1-piperazynil)-1,8-naphthyridine-3-carboxylic acid] (Fig. 1), another fluoroquinolone, shows a broad antimicro- bial spectrum. Its primary effect is the inhibition of bacterial DNA gyrase [1,2]. The widespread use of these compounds and the need for clinical and pharmacological study require fast and ∗ Corresponding author. Tel.: +34-958-243326; fax: +34-958-243328. E-mail address: anavalon@ugr.es (A. Naval´ on). 1 Present address: Faculty of Engineering, University of Zulia, P.O. Box 10259, Maracaibo, Venezuela. 2 Present address: Faculty of Agronomy, University of Zulia, P.O. Box 6610, Maracaibo, Venezuela. sensitive analytical methods for determination of its presence in biological fluids. Various techniques, including HPLC, spectrophotometry, spectrofluorimetry and voltammetry, have been proposed for the determination of ciprofloxacin and enoxacin [3–12]. Micellar liquid chromatography (MLC) represents an at- tractive alternative to conventional aqueous-organic mobile phases in clinical analysis [13,14]. Due to the existence of micelles, MLC has several unique advantages such as capability of simultaneous separation of hydrophobic and hydrophilic (polar and ionic) analytes, possibility of simul- taneous enhancement of solvent strength and separation se- lectivity, reproducible and predictable retention behaviour, possibility of direct injection of physiological samples, safety and cost [13]. MLC has been used for the analysis of therapeutic drugs [15], sulphonamides [16], anticancer drugs [17], -blockers [18], illegal drugs [19], steroids [20], cephalosporins [21] and diuretics [22] in biological fluids. This paper describes a MLC method for the simultaneous determination of CIPRO and ENO in human serum samples. 0003-2670/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2004.04.025