E Jiménez-Lozano

Determination of pKa values of quinolones from mobility and spectroscopic data obtained by capillary electrophoresis and a diode array detector

Abstract This work compares the values of dissociation constants obtained from electrophoretic mobilities of a series of quinolones at different pH values and those obtained using absorbance spectra at the maximum of the eletrophoretic peaks. The results obtained show that the two methods are complementary and constitute a valuable means of obtaining better precision. The two methods proposed can be used simultaneously without an increase in the experimental time and allow confirmation of the results obtained.

Comparison between capillary electrophoresis, liquid chromatography, potentiometric and spectrophotometric techniques for evaluation of pKa values of zwitterionic drugs in acetonitrile-water mixtures

Abstract Capillary electrophoresis, liquid chromatography, potentiometry and UV–visible spectrophotometry are frequently used for determination of pKa values of substances. In this work, we have compared the application of the different techniques to the determination of pKa values of a series of zwitterionic quinolones in acetonitrile–water mixtures, emphasizing the advantages of capillary electrophoresis for the determination of equilibrium constants of widely used drugs in aqueous and aqueous organic media.

Determination of residues of enrofloxacin and its metabolite ciprofloxacin in biological materials by capillary electrophoresis

A method for the analysis of enrofloxacin and ciprofloxacin in chicken muscle using marbofloxacin as internal standard is proposed. Clean-up and pre-concentration of the samples are effected by solid-phase extraction and determination is carried out by capillary electrophoresis using a photodiode array detector. The calibration graphs are linear for enrofloxacin and ciprofloxacin from 10 to 300 microg/kg. The method recoveries for enrofloxacin and ciprofloxacin are 74 and 54%, respectively. The limit of detection for the two compounds is lower than 25 microg/kg, which allows the detection of positive muscle samples at the required maximum residue limits.

Determination of residues of enrofloxacin and its metabolite ciprofloxacin in chicken muscle by capillary electrophoresis using laser-induced fluorescence detection.

A method for the residue analysis of the veterinary antimicrobial agent enrofloxacin and its active desethyl metabolite ciprofloxacin in chicken muscle tissue has been developed and validated. The detection of the analytes was performed by laser‐induced fluorescence (LIF) detection using a HeCd laser (λex = 325 nm) providing an enhancement in sensitivity and selectivity compared to conventional UV detection. The assay has been validated with satisfying results. The limits of quantification for enrofloxacin and ciprofloxacin were 5 νg/kg and 20 νg/kg, respectively, with a fivefold preconcentration yielded by a sample clean‐up with a simple liquid‐liquid extraction procedure. Calibration graphs were linear from 5 to 1000 νg/kg for enrofloxacin and from 20 to 1000 νg/kg for ciprofloxacin. The assay allows the detection of contaminated muscle samples at the required maximum residue limit of the European Union, which is 100 νg/kg for the sum of enrofloxacin and ciprofloxacin.

ELECTROPHORETIC BEHAVIOUR OF QUINOLONES IN CAPILLARY ELECTROPHORESIS: EFFECT OF PH AND EVALUATION OF IONIZATION CONSTANTS

Quinolones are a family of antibacterial agents that are used extensively in both human and veterinary clinics. Their antibacterial activity is pH-dependent, and therefore an examination of protonation equilibria in quinolone solution is essential. In this work, dissociation constants of quinolones in water were obtained using capillary electrophoresis (CE). The method is based on measuring the electrophoretic mobility of the solute as a function of pH. Mobility and pH data are fitted using different models. These developed equations have two advantages. They permit the determination of pKa of analytes with the advantages of CE and also permit the prediction of the effect of pH on the electrophoretic behaviour of substances and then the prediction of the pH optimum for the separation methods, using the minimum of experimental measurements.

Influence of pH and pKa values on electrophoretic behaviour of quinolones in aqueous and hydro-organic media

Through correct pH measurements, pKa and activity coefficient values, a model describing their effect on electrophoretic behaviour of substances is established. The suggested model uses the pH values in the acetonitrile-water mixtures used and takes into account the effect of activity coefficients. The model permits the calculation of acidity constants of analytes in hydro-organic media and also the prediction of the effect of pH on the electrophoretic mobility. The model is tested by determining the dissociation constants of a series of nine quinolones in acetonitrile-water mixtures of 0, 5.5, 10 and 30% (w/w) acetonitrile.

Determination of difloxacin and sarafloxacin in chicken muscle using solid-phase extraction and capillary electrophoresis

This paper describes a method for residue analysis of difloxacin and sarafloxacin in chicken muscle. Clean-up and preconcentration of the samples are effected by solid-phase extraction (C18) and the determination is carried out by capillary electrophoresis using a photodiode array detection system. The method was validated with satisfying results. The calibration graphs are linear for difloxacin and sarafloxacin from 50 to 300 microg/kg. The limit of detection obtained for difloxacin and sarafloxacin are 10 and 25 microg/kg, respectively, which allows the detection of positive muscle samples at the required maximum residue limits of European Union.

Evaluation of electrophoretic method versus chromatographic, potentiometric and absorptiometric methodologies for determing pKa values of quinolones in hydroorganic mixtures

The advantages of using capillary electrophoresis (CE) over other methodologies for determining pK(a) values of drugs in hydroorganic media are discussed. The focus of the discussion based upon the pK(a) values of a series of quinolones determined in acetonitrile (MeCN)--water mixtures by CE, liquid chromatography, potentiometric, and spectrophotometric methods.

Electrophoretic behaviour of zwitterionic compounds in capillary electrophoresis: Prediction of mobility of several quinolones

A model of electrophoretic behaviour is studied in order to optimize the separation of zwitterionic substances by capillary electrophoresis. The equations derived allow the electrophoretic mobilities of substances at each pH to be predicted and, consequently the resolution between pairs of substances. The model considers the effect of ionic strength and can be applied to zwitterionic substances with very close pKa values. The model is tested to obtain the optimum pH values for the separation of a series of eight quinolones on the basis of a few initial experiments.

Prediction of electrophoretic behaviour of a series of quinolones in aqueous methanol

Quinolones are a family of antibacterial agents used in human and veterinary clinics. The examination of protonation equilibria is essential because their antibacterial activity is pH-dependent. In this work, dissociation constants of quinolones in MeOH-water mixtures were obtained using capillary electrophoresis. The method is based on a model that relates electrophoretic mobility of the solute with pH. The effect of pH, pKa and activity coefficient on electrophoretic behaviour was considered. Standard pH values for buffer solutions were previously determined in MeOH-water mixtures, and the pH can thus be measured in these media as in water. This model is also used to obtain the optimum conditions for the separation of a series of substances because it allows one to predict the resolution between adjacent peaks from a few experimental data.