Development and validation of a QuEChERS method for the analysis of 5-nitroimidazole traces in infant milk-based samples by ultra-high performance liquid chromatography-tandem mass spectrometry.

QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) methodology in combination with UHPLC-MS/MS is proposed for the determination of 5-nitroimidazole (5-NDZ) residues in infant milk-based products. Chromatographic separation was accomplished in a C18 Zorbax Eclipse Plus RRHD (50 × 2.1 mm, 1.8 µm) column under gradient elution conditions. Mobile phase consisted of 0.025% (v/v) aqueous formic acid (eluent A) and MeOH (eluent B), and was supplied at a flow rate of 0.5 mL/min. Under these conditions, eleven 5-NDZs including three metabolites were separated in less than 4 min. A novel QuEChERS method was optimized, and primary-secondary amine (PSA) sorbent was selected as clean-up agent. In addition, the proposed QuEChERS procedure was compared with other sample preparation methodologies, which are usually used in the analysis of 5-NDZs, namely solid phase extraction (SPE) using mixed cation exchange (MCX) cartridges and molecularly imprinted solid phase extraction (MISPE). Method comparison was carried out in terms of process efficiency, which includes matrix effect and extraction recovery. Higher process efficiency was generally achieved for QuEChERS and MISPE than for SPE. However, matrix effect was more significant for the non-selective QuEChERS method than for the selective MISPE. Higher extraction recoveries (63.2-94.1%) were observed for QuEChERS. The studied methods were validated in terms of linearity, detection limits (CCα), detection capabilities (CCß) and precision, observing similar performance characteristics independently of the proposed sample treatment. CCα and CCß ranged between 0.05 and 1.69 µg/L for all analytes and extraction techniques. QuEChERS-UHPLC-MS/MS method was also validated in terms of precision (relative standard deviations <10.3%), trueness (recovery>70.2%) and selectivity according to Regulation 2002/657/EC. It is proposed as a good alternative for the monitoring of 5-NDZ residues in enriched infant-milk based products and other similar milk based-products.

Simple and rapid determination of 5-nitroimidazoles and metabolites in fish roe samples by salting-out assisted liquid-liquid extraction and UHPLC-MS/MS.

A novel multiresidue method is proposed for the determination of 12 5-nitroimidazoles and their metabolites in fish roe samples using UHPLC-MS/MS. A salting-out assisted liquid-liquid extraction procedure was performed prior to sample analysis. The separation of compounds was accomplished using a C18 Zorbax Eclipse Plus column (50 mm × 2.1 mm, 1.8 µm) at 25 °C and a mobile phase consisting of 0.025% (v/v) aqueous formic acid and pure MeOH at a flow rate of 0.5 mL/min. Parameters involved in ionization and fragmentation were also optimized. The method was characterized in terms of linearity (R2 ≥ 0.9992), extraction efficiency (≥68.9%), repeatability (RSD ≤ 9.8%), reproducibility (RSD ≤ 13.9%) and trueness (recoveries ≥81.4%). Decision limits (CCα) and detection capabilities (CCß) were obtained in the ranges 0.1-1.0 and 0.2-1.7 µg/kg, respectively.

A high-throughput UHPLC method for the analysis of 5-nitroimidazole residues in milk based on salting-out assisted liquid-liquid extraction.

A novel salting-out assisted liquid-liquid extraction (SALLE) method has been developed for the extraction of eight 5-NDZ antibiotics from milk samples prior to their analysis by UHPLC. An exhaustive study of the parameters involved in the SALLE procedure has been carried out, optimizing the extraction solvent volume, the amount of the salt agent, and the centrifugation and vortex timing by an experimental design. After sample treatment, the obtained extract was reconstituted in the mobile phase (6:94 (v/v) acetonitrile/water containing 0.1% (v/v) of formic acid) and analyzed by the proposed UHPLC-UV method. Separation was accomplished in a C18 Zorbax Eclipse Plus (50mm×2.1mm, 1.8µm) column at 45°C within 8min. Gradient mode was considered using a mobile phase consisting of 0.1% (v/v) formic acid aqueous solution and acetonitrile containing 0.1% (v/v) formic acid at a flow rate of 0.45mL/min. Analytical signals were monitored at 320nm. Matrix-matched calibration curves showed satisfactory linearity (R2≥0.996). LODs, ranging from 2 to 4µg/L, were achieved and precision studies showed RSDs lower than 12.8% in terms of peak height. Additionally, recoveries higher than 62.8% were obtained for all studied compounds in milk samples.

Capillary electrophoresis-tandem mass spectrometry combined with molecularly imprinted solid phase extraction as useful tool for the monitoring of 5-nitroimidazoles and their metabolites in urine samples.

A novel capillary electrophoresis-tandem mass spectrometry approach is proposed for the determination of eleven 5-nitroimidazoles in urine samples for therapeutical drug monitoring purposes. A comparison between two separation modes, namely micellar electrokinetic chromatography and capillary zone electrophoresis was carried out, obtaining higher selectivity when 1M formic acid (pH 1.8) was selected as background electrolyte. 5-Nitroimidazoles were hydrodynamically injected in water for 40s at 50mbar and their separation was performed at 28kV and 25°C. To improve migration time repeatability, a pressure of 50mbar was applied to the inlet vial during runs without any loss of peak resolution. Electrospray ionization parameters were established as follow: 6L/min, dry gas flow rate; 51,021.2Pa, nebulization pressure; 160°C, dry gas temperature. Sheath liquid consisted of a mixture of propan-2-ol/water/acetic acid (60.0:38.8:0.2% v/v/v) supplied at 3.3µL/min. MS parameters were optimized for analyte identification through their MS2 and MS3 spectra. The method was applied to the determination of 5-nitroimidazoles in urine samples, applying molecularly imprinted solid phase extraction for sample clean-up. Recoveries higher than 79.2% demonstrated the suitability of the procedure. Limits of detection ranged from 9.6 to 130.2µg/L while precision assays resulted in relative standard deviations for peak areas lower than 16.1%.

Evaluation of the combination of micellar electrokinetic capillary chromatography with sweeping and cation selective exhaustive injection for the determination of 5-nitroimidazoles in egg samples.

A methodology is presented for the sensitive determination of nitromidazole residues in egg by means of micellar electrokinetic capillary chromatography in combination with cation selective exhaustive injection and ultraviolet detection. Six compounds have been considered and the separation has been achieved in less than 12min in a 61.5-cm effective length capillary with 50-µm internal diameter. Phosphate buffer 44mM pH 2.5, containing 8% tetrahydrofurane and 123mM sodium dodecyl sulfate was employed as running buffer. Solid phase extraction has been employed for sample clean-up. The methodology has been successfully validated in hen eggs, obtaining method detection limits in the range of 2.1-5.0ng/g. Precision was studied in terms of repeatability and intermediate precision, with relative standard deviations lower than 18.0%. Recoveries were calculated in quail eggs and a commercial pasteurized egg white product, reaching over 70% for most of the considered 5-nitroimidazoles.

On-line preconcentration strategy for the simultaneous quantification of three local anesthetics in human urine using CZE.

The simultaneous determination of usually employed anesthetics (procaine, lidocaine, and bupivacaine) has been developed and validated using CE with ultraviolet detection at 212 nm. The separation of these three drugs has been achieved in less than 7 min, using a temperature of 25ºC and 25 kV, with a 150 mM citrate buffer (pH 2.5) as BGE. Field-amplified sample injection (FASI) has been used for on-line sample preconcentration. Ultrapure water and ACN 50/50 (v/v) mixture gave the greatest enhancement factor when it was employed as an injection solvent. Injection voltage and time were optimized, being 13 kV and 13 s, the optimum values, respectively. To avoid the possible irreproducibility associated with the electrokinetic injection, an internal standard such as tetracaine, was employed. The instrumental detection limits (LOD S/N = 3) for the compounds ranged between 2.6 and 7.0 µg L(-1) and the quantitation limits (LOQ S/N = 10) between 37.8 and 55.9 µg L(-1) . The detection limits obtained in real human urine samples ranged between 55.2 and 83.6 µg L(-1) and the quantitation limits between 196.0 and 276.0 µg L(-1) . The proposed method has demonstrated its applicability to the analysis of these local anesthetics in urine samples without any pretreatment, allowing the rapid determination of these target analytes.

Determination of 5-nitroimidazole residues in milk by capillary electrochromatography with packed C18 silica beds.

This work presents a novel methodology for analysing 5-nitroimidazole residues in milk samples by capillary electrochromatography using lab-made packed columns, produced by carrying out a high pressure packing procedure using acetone as driving solvent and C18 silica uncapped particles (5 µm particle size) as packing material. Column frits resulted from sintering the proper stationary phase by heating the packed material for 20s with a nichrome ribbon (80% Ni-20% Cr, 28 cm × 2 mm × 0.2 mm, electric resistance 1.3 Ω) connected to a 7 V AC power supply. Lab-made C18 silica packed capillaries (40 cm x 50 µm i.d.) were employed for the determination of 5-nitroimidazole drugs. Milk samples were treated by a salting-out assisted liquid-liquid extraction followed by a solid phase extraction with Oasis®HLB cartridges prior to their injection. Samples were hydrodynamically injected into the column for 120 s at 11.5 bar. Afterwards eight 5-nitroimidazole compounds were separated in isocratic mode under an applied voltage of 27 kV and a temperature of 30 °C. The selected mobile phase consisted of a mixture 60:40 acetonitrile:ammonium acetate (2.5 mM, pH=5). Separation was monitored at 320 nm and it was performed in less than 15 min. The method was characterized in terms of linearity (R(2)≥0.993) and precision (repeatability, RSD≤12.2% and reproducibility, RSD≤14.5%), obtaining detection limits lower than 29 µg/L for all compounds under study.

Development of an ultrasensitive stacking technique for 5-nitroimidazole determination in untreated biological fluids by micellar electrokinetic chromatography.

Cation-selective exhaustive injection and sweeping followed by a MEKC separation is evaluated for the sensitive analysis of 5-nitroimidazoles in untreated human serum and urine. Deproteinized serum and urine samples were diluted 76 and 143 times, respectively, in a low-conductivity solvent (5.00 mM orthophosphoric acid containing 5.0% v/v methanol). Samples were electrokinetically injected at 9.8 kV for 632 s in a previously conditioned fused-silica capillary (65.0 cm × 50 µm id). Separation was performed at -30 kV and 20°C using 44 mM phosphate buffer (pH 2.5), 123 mM SDS, and 8% v/v tetrahydrofurane as BGE. Signals were monitored at 276 nm and peak area was selected as analytical response. Good linearity (R(2) ≥ 0.988) and LODs lower than 1.5 and 1.8 µg/mL were achieved in serum and urine, respectively.

Ultrasensitive analysis of lysergic acid diethylamide and its C-8 isomer in hair by capillary zone electrophoresis in combination with a stacking technique and laser induced fluorescence detection.

This article deals with the development and validation of a novel capillary zone electrophoresis (CZE) with laser induced fluorescence detection method for the analysis of lysergic acid diethylamide (LSD) and its isomer iso-LSD in hair samples. The separation of both analytes has been achieved in less than 13 min in a 72-cm effective length capillary with 75-µm internal diameter. As running buffer 25 mM citrate, pH 6.0 has been employed and separation temperature and voltage of 20 °C and 13 kV respectively, were applied. Field amplified sample injection (FASI) has been employed for on-line sample preconcentration, using ultrapure water containing 117 µM H3PO4 as optimum injection medium. Injection voltage and time have been optimized by means of experimental design, obtaining values of 7 kV and 15s, respectively. Methylergonovine has been employed as internal standard in order to compensate irreproducibility from electrokinetic injection. The analytical method has been applied to hair samples, previous extraction of the target analytes by ultrasound assisted solid-liquid extraction at 40 °C for 2.5 h, employing acetonitrile as extracting solvent. Linear responses were found for LSD and iso-LSD in matrix-matched calibrations from around 0.400 up to 50.0 pg mg(-1). LODs (3 S/N) in the order of 0.100 pg mg(-1) were calculated for both analytes, obtaining satisfactory recovery percentages for this kind of sample.

Multiresidue analysis of quinolones in water by ultra-high perfomance liquid chromatography with tandem mass spectrometry using a simple and effective sample treatment.

A rapid and simple analytical method has been developed for the determination of 19 quinolones in environmental water samples using ultra high performance liquid chromatography with tandem mass spectrometry. Chromatographic and detection conditions have been optimized and the separation was achieved in less than 4 min. The separation was carried out using a new-generation column filled with superficially porous particles, resulting in lower backpressure and better resolution than totally porous particle columns. The quinolones were detected by electrospray ionization in positive mode using multiple-reaction monitoring mode for acquisition. A sample treatment based on liquid-liquid extraction and phase separation via salting-out was employed to achieve a fast and simple extraction that enables the multiresidue analysis. The method has been validated for an environmental well water sample from a mountain area. Very low limits of detection (between 10 and 90 ng/L) with relative standard deviations lower than 16.5% and recoveries higher than 73% were achieved. Moreover, well waters from different origins (mountain and coast areas and irrigated land) have been evaluated and similar results were obtained.

Novel cation selective exhaustive injection-sweeping procedure for 5-nitroimidazole determination in waters by micellar electrokinetic chromatography using dispersive liquid-liquid microextraction.

A novel method consisting of cation-selective exhaustive injection and sweeping (CSEI-sweeping) as on-line preconcentration followed by a micellar electrokinetic chromatography (MEKC) separation has been developed for the determination of 5-nitroimidazoles (5-NDZ) in environmental waters. Moreover, dispersive liquid-liquid microextraction (DLLME) has been proposed for first time as sample treatment technique prior to CSEI-sweeping-MEKC. DLLME was applied to 5mL of sample. Dibromomethane (1156µL) and 2-butanol (1363µL) were employed as extractant and dispersive solvents, respectively. Salting-out effect was achieved by the addition of 16% (w/v) NaCl to the samples. After DLLME and organic solvent evaporation, the residue was redissolved in a low conductivity solvent (5mM phosphoric acid with 5% of methanol) and electrokinetically injected at 9.8kV for 632s in a bare fused-silica capillary (57.2cm, 50µm I.D.). Prior to the injection, the capillary was rinsed with 50mM phosphate buffer pH 2.5, followed by a plug of a higher conductivity buffer (100mM phosphate pH 2.5, 50mbar, 264s) and a plug of water (50mbar, 2s). Separation was carried out applying -30kV at 20°C in 44mM phosphate buffer pH 2.5, containing 8% tetrahydrofuran and 123mM sodium dodecyl sulfate. Analytical signals were monitored at 276nm. Validation was performed in river and well waters, obtaining satisfactory results in terms of linearity, precision (% RSD generally lower than 10%) and trueness (recoveries higher than 70% in almost all cases). LODs ranged from 0.61 to 2.44ng/mL. The combination of this microextraction technique with the proposed capillary electrophoresis methodology supposes a simple, sensitive and cheap alternative for 5-NDZ analyses, in accordance with the aims of green chemistry.

Novel solid phase extraction method for the analysis of 5-nitroimidazoles and metabolites in milk samples by capillary electrophoresis.

A new sample treatment has been developed for the extraction of 5-nitroimidazole (5-NDZ) drugs in milk samples previous to their determination by micellar electrokinetic chromatography (MEKC). Fat removing and protein precipitation were simultaneously carried out by the addition of trichloroacetic acid (TCA) and subsequent centrifugation. Clean-up and off-line concentration were achieved by a novel solid-phase extraction (SPE) method employing mixed cation exchange (MCX) cartridges, obtaining an off-line concentration factor of 18. Analyses were performed in less than 18 min employing 20mM phosphate buffer (pH 6.5) and 150 mM SDS as background electrolyte (BGE). During the separation procedure a temperature of 20 °C and a voltage of 25 kV (normal mode) were applied. Due to sweeping effects, an on-line concentration was achieved for all the studied compounds and detection limits lower than 1.8 µg L(-1) were obtained. This method has been successfully applied to milk samples of different origins, including raw ewe milk.

Green methodology based on dispersive liquid-liquid microextraction and micellar electrokinetic chromatography for 5-nitroimidazole analysis in water samples.

Dispersive liquid-liquid microextraction has been proposed as an extraction technique combined with micellar electrokinetic chromatography (MEKC) for the analysis of eight 5-nitroimidazole compounds, including some metabolites, in water samples. Determination has been carried out using a diode array detector, employing 20 mM sodium phosphate and 150 mM SDS as separation buffer. Separation has taken place under a voltage of 25 kV and a temperature of 20°C. Samples were prepared in a buffer without micelles and they were hydrodynamically injected at 50 mbar for 25 s, producing a sweeping effect on the analytes for increasing sensitivity. Different factors involved in the dispersive liquid-liquid microextraction procedure were optimized, such as sample pH, nature, and volume of extraction and dispersive solvents in the mixture, percentage of NaCl added to sample and shaking time after the injection of the extraction and dispersive solvents. The method was characterized for water samples, achieving detection limits lower than 2.4 µg/L. Trueness was checked in river, tap, and bottled water. Dispersive liquid-liquid microextraction combined with MEKC constitutes an easy, cheap, and green alternative for 5-nitroimidazole analysis in environmental water samples.

Dispersive liquid-liquid microextraction prior to field-amplified sample injection for the sensitive analysis of 3,4-methylenedioxymethamphetamine, phencyclidine and lysergic acid diethylamide by capillary electrophoresis in human urine.

A novel capillary zone electrophoresis (CZE) with ultraviolet detection method has been developed and validated for the analysis of 3,4-methylenedioxymethamphetamine (MDMA), lysergic acid diethylamide (LSD) and phencyclidine (PCP) in human urine. The separation of these three analytes has been achieved in less than 8 min in a 72-cm effective length capillary with 50-µm internal diameter. 100 mM NaH(2)PO(4)/Na(2)HPO(4), pH 6.0 has been employed as running buffer, and the separation has been carried out at temperature and voltage of 20°C, and 25kV, respectively. The three drugs have been detected at 205 nm. Field amplified sample injection (FASI) has been employed for on-line sample preconcentration. FASI basically consists in a mismatch between the electric conductivity of the sample and that of the running buffer and it is achieved by electrokinetically injecting the sample diluted in a solvent of lower conductivity than that of the carrier electrolyte. Ultrapure water resulted to be the better sample solvent to reach the greatest enhancement factor. Injection voltage and time have been optimized to 5 kV and 20s, respectively. The irreproducibility associated to electrokinetic injection has been correcting by using tetracaine as internal standard. Dispersive liquid-liquid microextraction (DLLME) has been employed as sample treatment using experimental design and response surface methodology for the optimization of critical variables. Linear responses were found for MDMA, PCP and LSD in presence of urine matrix between 10.0 and 100 ng/mL approximately, and LODs of 1.00, 4.50, and 4.40 ng/mL were calculated for MDMA, PCP and LSD, respectively. The method has been successfully applied to the analysis of the three drugs of interest in human urine with satisfactory recovery percentages.

Determination of quinolones of veterinary use in bee products by ultra-high performance liquid chromatography-tandem mass spectrometry using a QuEChERS extraction procedure.

A reliable and rapid ultra high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method has been developed for the determination of the eight quinolones of veterinary use regulated by European Union (marbofloxacin, ciprofloxacin, danofloxacin, enrofloxacin, sarafloxacin, difloxacin, flumequine and oxolinic acid). Chromatographic conditions were optimized in order to increase sample throughput and sensitivity. The antibiotics were detected by electrospray ionization in positive ion mode with multiple reaction monitoring (MRM) and MS/MS conditions were optimized in order to increase selectivity, selecting the corresponding product ions for quantification and identification. The separation was achieved in 3 min, using a Zorbax Eclipse Plus C18 column (50 mm × 2.1mm, 1.8 µm), with a mobile phase of 0.02% aqueous formic acid solution and acetonitrile. A dispersive solid phase extraction methodology, often referred to as the "QuEChERS" (quick, easy, cheap, effective, rugged, and safe) method, was optimized for extraction of the quinolones from honey and also it was evaluated for other bee products such as royal jelly and propolis. The method was validated for each matrix in terms of linearity, trueness, precision, limits of detection (LODs) and quantification (LOQ). LODs ranged between 0.2 and 4.1 µg kg(-1) with precision lower than 12% and satisfactory recoveries in most cases. The method was also applied for studying the occurrence of these antibiotics in several market samples.

Determination of 5-nitroimidazoles and metabolites in environmental samples by micellar electrokinetic chromatography.

A method based on micellar electrokinetic chromatography (MEKC) with UV detection has been developed for the determination of nine 5-nitroimidazoles (5-NDZs), including metabolites in river water samples. Due to the relative insensitivity of UV detection in MEKC, a solid-phase extraction (SPE) method has been proposed that preconcentrates water samples fiftyfold and cleans them up off-line. An on-line preconcentration approach based on sweeping and the use of an extended light path fused-silica capillary (64.5 cm × 50 µm i.d., 56 cm effective length) was also found to improve the sensitivity of the method. Separation was carried out in <21 min using 20 mM phosphate buffer (pH 6.5) and 150 mM SDS as the background electrolyte (BGE). The temperature of the capillary was kept constant at 20°C, a voltage of 25 kV was applied (normal mode), and a detected wavelength of 320 nm was utilized. Hydrodynamic injection (50 mbar for 15 s) of the samples, which were dissolved in 20 mM phosphate (pH 6.5), was employed. The limits of detection were lower than 1.1 µg L(-1). Recoveries of >80% from spiked river water samples were obtained for most of the analytes at three different concentration levels with acceptable precision. This method could provide an efficient and economical alternative to the use of chromatographic methods to monitor nitroimidazole residues, thus supplementing the relatively few methods available for the analysis of these compounds in environmental samples.

Comparison of different sample treatments for the analysis of quinolones in milk by capillary-liquid chromatography with laser induced fluorescence detection.

A simple and very sensitive capillary-liquid chromatography method coupled with laser induced fluorescence detection has been developed for the simultaneous determination of seven quinolones of veterinary use in milk. Moreover, a comparison between two different sample treatments (QuEChERS and molecularly imprinted polymer, MIP) has been carried out in terms of efficiency of the extraction (number of analytes to be analysed and absence of interferences), throughput, linear dynamic range in matrix-matches calibrations, detection and quantification limits and accuracy (trueness and precision, by means of recovery assays). The results showed that the QuEChERS procedure was more efficient and faster, showing good recoveries, sensitivity and precision for all the studied compounds. Employing this proposed method, very low detection limits, between 0.4 µg/kg for danofloxacin, and 6 µg/kg for sarafloxacin, have been obtained.

Laser induced fluorescence coupled to capillary electrophoresis for the determination of fluoroquinolones in foods of animal origin using molecularly imprinted polymers.

A method for the simultaneous determination of four fluoroquinolones of veterinary use (ciprofloxacin, danofloxacin, enrofloxacin and sarafloxacin) in two complex matrixes, such as bovine raw milk and pig kidney, has been established and validated. The method is based on the use of capillary electrophoresis (CE) coupled with a very sensitive detection mode, such as laser induced fluorescence (LIF) detection, due to the fact the all the compounds selected show native fluorescence. In order to achieve high selectivity in the sample treatment procedure, a commercially available molecularly imprinted polymer has been used for the solid phase extraction of the analytes. Once the retention and elution processes were optimized, the final extract was analyzed by CE-LIF using a 325 nm He-Cd laser. Optimum separation was obtained in a 70 cm x75 microm capillary using a 125 mM phosphoric acid solution at pH 2.8 with 36% methanol as background electrolyte. The method provided very low detection limits, ranging from 0.17 to 0.98 microg/kg for milk and 1.10 to 10.5 microg/kg for kidney, with acceptable precision and satisfactory recoveries.

Sensitive determination of fluoroquinolone residues in waters by capillary electrophoresis with laser-induced fluorescence detection.

A sensitive capillary electrophoresis-laser-induced fluorescence method has been developed for the determination of six fluoroquinolones of human (ofloxacin, lomefloxacin, and norfloxacin) and veterinary use (danofloxacin, enrofloxacin, and sarafloxacin) in different kinds of water. Fluorescence detection was achieved using a He-Cd laser, with a wavelength of 325 nm. Separation was performed in a fused-silica capillary, and conditions were optimized to obtain the most adequate separation and with the best sensitivity. The separation was carried out in a 70-cm-long capillary (75 microm internal diameter, effective length 55 cm) by using a 125 mM phosphoric acid separation buffer at pH 2.8, with 36% of methanol. The water sample pretreatment involved the separation and preconcentration of the analytes by solid phase extraction. Two reverse-phase cartridges have been evaluated, namely Oasis hydrophilic-liphophilic balance and Strata-X; the latter provided the best recoveries for the selected analytes. The method shows very low detection limits (0.3-1.9 ng/L) with acceptable recoveries and precisions and has been successfully applied to the analysis of well and tap water samples.

Applications of capillary electrophoresis to the determination of antibiotics in food and environmental samples.

In this paper we review applications of capillary electrophoresis (CE) to the determination of antibiotic residues in food derived from animals and in environmental samples. Although many CE methods have been used to determine antibiotics in the pharmaceutical field (drug quality control or therapeutic monitoring in biological samples), food and environmental applications have been increasing in recent years. Due to the maximum residue limits established by the EU, in Directive 2377/90/EEC, for foodstuffs of animal origin and considering the low levels that can be found in environmental or waste waters or soils, different strategies to increase sensitivity have been developed, including off-line preconcentration, on-line stacking modes to use higher sample volumes, or in-line solid-phase extraction. Also, several detection techniques, such as fluorescence, laser-induced fluorescence, electrochemical detection, or mass spectrometry have been used; the last of these also enables unequivocal identification of the residues, required by Commission Decision 2002/657/EC. All these aspects will be discussed in this paper, in relation to the main groups of antibiotics used in veterinary and human medicine, for which applications in food and environmental samples have been developed by using CE as an efficient alternative to liquid chromatography.