803Fluoroquinolones are a class of synthetic antibacterial agents, which are known for their broad spectrum of antibacterial activity. These compounds are derived from nalidixic acid and naphthyridine derivatives, which have been introduced for clinical applications in the livestock and farming industries.1 In this work, two important fluoroquinolones, namely enrofloxacin (1-cyclopropyl-7-(4-ethyl-1-piperazinyl)-6-fluoro-1,4-dihydro-4-oxo-3-quinolonecarboxylic acid) and ciprofloxacin (1-cyclopropyl-7-(1-piperazinyl)-6-fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid), were investigated and quantitatively analyzed by voltammetric methods. In several animal species, including pigs, enrofloxacin (ENRO) is de-ethylated to its primary metabolite, ciprofloxacin (CIPRO), 2 and both ENRO and CIPRO are found in the bile and urine of animals receiving ENRO. Electrochemical methods, such as polarography and voltammetry, have high sensitivity and are widely used in many areas of analytical chemistry.Recently, cathodic adsorptive stripping voltammetry on a static mercury drop electrode and principal-component regression have been applied for the determination of ENRO in the presence of CIPRO 10 at trace levels. However, the linear dynamic range of the method is too narrow, and the toxicity of mercury (as an electrode) has caused its application in routine laboratories to decline. At more negative potentials, many biological compounds are adsorbed on the surface of the Hg-electrode, diminishing the selectivity of the method. 10 On the other hand, simultaneous voltammetric determinations of ENRO and CIPRO have not been reported, since ENRO affects the oxidation potential of CIPRO and vice versa. Therefore, the direct determination of CIPRO in the presence of ENRO is not possible by univariate calibration methods.In this work, linear sweep voltammetry (LSV) used for the first time with a multiwall carbon nanotubes/glassy carbon electrode (MWCNT/GCE) provides a sensitive method for the determination of ENRO or CIPRO in the presence of the other without any pretreatment or separation. When MWCNT/GCE is used as a working electrode in the voltammetric method, ENRO affects the oxidation potential of CIPRO, whereas CIPRO does not affect that of ENRO. Because it was possible to measure ENRO without any interfering effect of CIPRO, a least-squares support vector machine (LS-SVM) model was constructed in this study to relate a CIPRO voltammogram to its concentration. The model predicts CIPRO concentration in both spiked human plasma and pharmaceutical samples. The proposed methodology is fast and simple, while it does not generate hazardous chemical wastes.
Theory of Least Square Support Vector RegressionSupport vector machines (SVMs) based on statistical learning theory were introduced by Cortes and Vapnik.11 LS-SVMs are an alternate formulation of SVM described by Suykens et al. 12 Here, we only briefly describe the theory of LS-SVM. Linear least-squares models fit a linear relation between the spectrum xi and the reference va...
