Microchim. Acta 148, 227–233 (2004) DOI 10.1007/s00604-004-0265-8 Original Paper Determination of the Antibacterial Drug Enrofloxacin by Solid-Phase Spectrofluorimetry Oscar Ballesteros, Jose ´ Luis Vı ´lchez, Jalila Taoufiki, and Alberto Navalo ´n  Research Group of Analytical Chemistry and Life Sciences, Department of Analytical Chemistry, University of Granada, Avda. Fuentenueva s=n, E-18071 Granada, Spain Received February 2, 2004; accepted June 24, 2004; published online November 5, 2004 # Springer-Verlag 2004 Abstract. A method for the determination of trace amounts of enrofloxacin based on solid-phase spectro- fluorimetry has been developed. The relative fluores- cence intensity of enrofloxacin fixed on Sephadex SP C-25 gel was measured directly after packing the gel beads in a 1-mm silica cell, using a solid-phase attach- ment. The wavelengths of excitation and emission were 277 and 448nm, respectively. The linear con- centration range of application was 0.2–4.0 ng mL 1 of enrofloxacin, with a relative standard deviation of 1.2% (for a level of 2.0 ng mL 1 ) and a detection limit of 0.04 ng mL 1 . The method was applied to the deter- mination of enrofloxacin in commercial pharmaceuti- cal formulations and spiked canine serum samples. It was validated using HPLC as a reference method and applying the standard addition methodology. Recovery levels of the method reached 100% in all cases. Key words: Enrofloxacin; solid-phase spectrofluorimetry; anti- bacterials; fluoroquinolones; serum analysis. Fluoroquinolones are an important group of synthetic antibacterial agents developed in recent years which are widely used in human and veterinary medicine. These compounds exhibit high activity against a broad spectrum of gram-negative and gram-positive bacteria through inhibition of their DNA gyrase [1–3]. Their common skeleton is 4-oxo-1,4-dihydroquino- line, where the pharmacologic unit consists of a pyr- idine ring with a carboxyl group, a piperazinyl group and a fluorine atom placed at position 3, 7 and 6, respectively. The use of these drugs has become a serious prob- lem in the case of livestock animals affected by infec- tious diseases, as they are substances leaving residues in edible tissues which may be directly toxic or cause resistance to human pathogens as well as possible allergic hypersensitivity reactions in humans [4, 5]. To ensure human food safety, the European Union has set tolerance levels for these compounds in animal products [6]. Therefore, the development or improve- ment of analytical methods for the determination of these drugs at trace level is of increasing interest. Enrofloxacin (ENRO) [1-cyclopropyl-7-(4-ethyl-1- piperazinyl)-6-fluoro-1,4-dihydro-oxo-3-quinoline- carboxylic acid] (Fig. 1) is a synthetic fluoroquinolone derivative which has demonstrated broad-spectrum activity against many pathogenic gram-negative and gram-positive bacteria. This synthetic antibiotic is widely used in the treatment of various infections in cats, dogs, pigs, chicken, turkeys and fish [7]. Different techniques have been proposed for the determination of ENRO, i.e., high-performance liquid chromatography (HPLC) [8–17], capillary electropho- resis [18], spectrofluorimetry [19], differential-pulse  Author for correspondence. E-mail: anavalon@ugr.es