D. Barrón

Improved determination of quinolones in milk at their MRL levels using LC–UV, LC–FD, LC–MS and LC–MS/MS and validation in line with regulation 2002/657/EC

This paper reports the multi-residue determination of quinolones included in the European Union regulations (marbofloxacin, ciprofloxacin, danofloxacin, enrofloxacin and flumequine) in bovine milk, using liquid chromatography with ultraviolet (LC-UV), fluorescence (LC-FD), mass spectrometry (LC-MS) and tandem mass spectrometry detection (LC-MS/MS). The methods were validated, in line with EU requirements (Commission Decision 2002/657/EC). Linearity, decision limit (CCalpha), detection capability (CCbeta), detection limit (LOD), quantification limits (LOQ), recoveries, precision, selectivity and stability were determined and adequate results were obtained. Recoveries higher than 80% were obtained for all quinolones. The methods developed were used to quantify enrofloxacin and its main metabolite, ciprofloxacin, in milk from animals treated with enrofloxacin.

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.

Spectrophotometric, potentiometric and chromatographic pKa values of polyphenolic acids in water and acetonitrile–water media

The pKa values of nine polyphenolic acid substances in water and acetonitrile–water mixtures using potentiometric, spectrophotometric, and liquid chromatographic (LC) measurements, have been determined. Also, a new method based on the absorbance spectra at the maximum of chromatographic peaks previously obtained has been applied. This method can be applied to data obtained from LC–UV (diode array detection (DAD)) instruments and retains all the advantages of LC and spectrophotometric methods, such as the possibility of working with impure samples. Finally, the advantages of the different methods to the determination of pKa values of nine polyphenolic acids have been described in order to verify the applicability of the proposed methods in aqueous and acetonitrile–water media.

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.

Comparative study of the LC–MS/MS and UPLC–MS/MS for the multi-residue analysis of quinolones, penicillins and cephalosporins in cow milk, and validation according to the regulation 2002/657/EC

The aim of this study was to develop and validate an analytical method to simultaneously determine European Union-regulated β-lactams (penicillins and cephalosporins) and quinolones in cow milk. The procedure involves a new solid phase extraction (SPE) to clean-up and pre-concentrate the three series of antibiotics before analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). LC-MS/MS and UPLC-MS/MS techniques were also compared. The method was validated according to the Directive 2002/657/EC and subsequently applied to 56 samples of raw cow milk supplied by the Laboratori Interprofessional Lleter de Catalunya (ALLIC) (Laboratori Interprofessional Lleter de Catalunya, Control Laboratory Interprofessional of Milk of Catalunya).

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.

The application of factor analysis to solvatochromic parameters and pHs values for the standardization of potentiometric sensors in mobile phases used in liquid chromatography

Abstract The pH s values for reference buffer solutions in aqueous acetonitrile, methanol, and tetrahydrofuran mixtures used as mobile phases in LC were subjected to factor analysis in order to discover the number of factors which affect the variation with the percentage of organic co-solvent of the whole data sets. Afterwards, target factor analysis was used to identify these factors. The pH s values were correlated with the solvatochromic parameters (π*, α, β, and E T ) of the hydro-organic mixtures according to the results obtained using these chemometric techniques. An equation is proposed which permits the calculation of pH s values in any aqueous acetonitrile, methanol, or tetrahydrofuran mixtures, and thus accurate pH measurements can be made in these media as well as in water. An overview of the effects on pH s values of preferential solvation in these media is also presented.

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.

Determination of multiresidue quinolones regulated by the European Union in pig liver samples ☆: High-resolution time-of-flight mass spectrometry versus tandem mass spectrometry detection

The use of liquid chromatography coupled to orthogonal acceleration time-of-flight mass spectrometry (LC-ToF-MS) provides an attractive alternative to liquid chromatography coupled to quadrupole (LC-MS) or triple quadrupole mass spectrometry (LC-MS/MS) in multiresidue analysis. ToF-MS provides accurate mass information and a significantly higher mass resolution than quadrupole analyzers. In this work, the influential parameters in time-of-flight detection using an electrospray ionization (ESI) source were studied using a central composite design to obtain the main effects and their two-factor interactions. The method developed uses LC-ESI-ToF-MS to determine and characterize quinolones regulated by the EU in pig liver samples below the maximum residue limits (MRLs). Linearity, decision limit, detection capability, detection and quantification limits, precision and recoveries were determined and adequate results were obtained, with quantification limits between 1.5 and 6 microg kg(-1) and recoveries higher than 60% for all quinolones. Limits of detection are lower than 2 microg kg(-1). Results obtained using LC-ESI-ToF-MS were compared with those obtained using LC coupled to a quadrupole and to triple quadrupole mass spectrometer. The work described in this paper illustrates the suitability and excellent confirmatory potential of LC-ToF-MS for multiresidue analysis in food samples.