Target and Suspect Screening of Pharmaceuticals and their Transformation Products in the Klip River, South Africa, using Ultra-High-Performance Liquid Chromatography-Mass Spectrometry.

In spite of recent reports about the presence of pharmaceuticals in African water bodies, their prevalence has still not been sufficiently quantified. The few available studies have mostly focused on a limited number of pharmaceuticals. In the present study, a suspect screening of 92 compounds (mainly pharmaceuticals and their transformation products) along the Klip River, South Africa was conducted, followed by target monitoring of 21 of the detected pharmaceuticals. The experimental approach was based on solid-phase extraction followed by analysis with ultra-high-performance liquid chromatography-quadrupole time-of-flight-mass spectrometry (UHPLC-QTOF-MS). The results revealed 47 pharmaceuticals, 31 of which were detected for the first time in South African waters. Seven detected pharmaceuticals (propyphenazole, sulfamerazine, levamisole, tryptophan, dibucaine, albuterol, and fenpropimorph) are not approved medications in South Africa. Six pharmaceutical metabolites were detected for the first time in South Africa. Pharmaceuticals with the highest concentrations in river water were flumequine (0.257 µg L-1 ), oxolinic acid (0.355 µg L-1 ), and acetaminophen (0.432 µg L-1 ). Oxolinic acid presented the highest hazard quotient, 48.6, indicating a risk of toxicity to aquatic organisms. Hazard quotients for other pharmaceuticals were below 1, except that of flumequine, which reached 1.285. These results suggest a need for further research into the fate of pharmaceuticals in surface waters, and a quantification of the risks associated with the identified drugs because they are likely to accumulate in the tissues of fish/aquatic organisms, thus affecting humans. Environ Toxicol Chem 2022;41:437-447. © 2021 SETAC.

Validation of a procedure to quantify oxolinic acid, danofloxacin, ciprofloxacin and enrofloxacin in selected meats by micellar liquid chromatography according to EU Commission Decision 2002/657/EC.

The suitability of an analytical method to determine oxolinic acid, danofloxacin, ciprofloxacin and enrofloxacin in edible tissues, based on micellar liquid chromatography coupled with fluorescence detection, to be applied in chicken, turkey, duck, lamb, goat, rabbit and horse muscle, is described. The method was fully matrix-matched in-lab revalidated, for each antimicrobial drug and meat, following the guidelines of the EU Commission Decision 2002/657/EC. The permitted limits were the maximum residue limits stated by the EU Commission Regulation 37/2010. The results obtained for the studied validation parameters were in agreement with the guidelines: selectivity (the antibiotics were resolved), linearity (r2  > 0.995), limit of detection (0.004-0.02 mg/kg), limits of quantification (0.01-0.05 mg/kg), calibration range (up to 0.5 mg/kg), recovery (89.5-105.0%), precision (<8.3%), decision limit, detection capability, ruggedness, stability and application to incurred samples. The method was found to be able to provide reliable concentrations with low uncertainty within a large interval, including the maximum residue limits, and then was useful to find out prohibited contaminated samples. The method did not require to be adapted for these matrices, and then it maintained its interesting advantages: short-time, eco-friendly, safe, inexpensive, easy-to-conduct, minimal manipulation and useful for routine analysis.

Determination of oxolinic acid, danofloxacin, ciprofloxacin, and enrofloxacin in porcine and bovine meat by micellar liquid chromatography with fluorescence detection.

A method was developed for the determination of oxolinic acid, danofloxacin, ciprofloxacin and enrofloxacin by micellar liquid chromatography - fluorescence detection in commercial porcine and bovine meat. The samples were ultrasonicated in a micellar solution, free of organic solvent, to extract the analytes, and the supernatant was directly injected. The quinolones were resolved in <22min using a mobile phase of 0.05M SDS - 7.5% 1-propanol - 0.5% triethylamine buffered at pH 3, running through a C18 column at 1mL/min using isocratic mode. The method was validated by the in terms of: selectivity, calibration range (0.01-0.05 to 0.5mg/kg), linearity (r2>0.9998), trueness (89.3-105.1%), precision (<8.3%), decision limit (<12% over the maximum residue limit), detection capability (<21% over the maximum residue limit), ruggedness (<5.6%) and stability. The procedure was rapid, eco-friendly, safe and easy-to-handle.

Environmental impact assessment of veterinary drug on fish aquaculture for food safety.

The degradation of veterinary drugs approved for use in aquaculture is very important in the evaluation of the impact of these drugs on the environment and to ensure safe food production. The purpose of this study is to provide guidance on how the interpretation of environmental fate data can be used by applicants to aid in protecting the environment and for the basis for food production, by suggesting the correct interpretation of data as part of an effective registration process. Tests were performed using a modification of the Organisation for Economic Co-operation and Development (OECD) 308 guideline using erythromycin and oxolinic acid under combinations of aerobic and anaerobic conditions, with and without sediment, in sea water and fresh water. Estimated DT50 s of erythromycin in fresh and sea water ranged from 6.8 to 37.9 days and estimated DT90 s were from 22.6 to 125.9 days. Degradation was more rapid in fresh water than in sea water with the formation of three degradation products: anhydroerythomycin A, erythromycin A enol ether, and pseudoerythomycin A enol ether. Estimated DT50 s of oxolinic acid in fresh and sea water were from 10.3 to 63.0 days and estimated DT90 s were from 34.3 to 209.4 days which suggests that oxolinic acid is more persistent in the environment than erythromycin. Copyright © 2016 John Wiley & Sons, Ltd.

Use of micellar liquid chromatography to analyze oxolinic acid, flumequine, marbofloxacin and enrofloxacin in honey and validation according to the 2002/657/EC decision.

A micellar liquid chromatographic method was developed for the analysis of oxolinic acid, flumequine, marbofloxacin and enrofloxacin in honey. These quinolines are unethically used in beekeeping, and a zero-tolerance policy to antibiotic residues in honey has been stated by the European Union. The sample pretreatment was a 1:1 dilution with a 0.05M SDS at pH 3 solution, filtration and direct injection, thus avoiding extraction steps. The quinolones were eluted without interferences using mobile phase of 0.05M SDS/12.5% 1-propanol/0.5% triethylamine at pH 3, running at 1mL/min under isocratic room through a C18 column. The analytes were detected by fluorescence. The method was successfully validated according to the requirements of the European Union Decision 2002/657/EC in terms of: specificity, linearity (r(2)>0.995), limit of detection and decision limit (0.008-0.070mg/kg), lower limit of quantification (0.02-0.2mg/kg), detection capability (0.010-0.10mg/kg), recovery (82.1-110.0%), precision (<9.4%), matrix effects, robustness (<10.4%), and stability. The procedure was applied to several commercial honey supplied by a local supermarket, and the studied antibiotics were not detected. Therefore, the method was rapid, simple, safe, eco friendly, reliable and useful for the routine analysis of honey samples.

Development and validation of a method for the simultaneous extraction and separate measurement of oxytetracycline, florfenicol, oxolinic acid and flumequine from marine sediments.

A simple and rapid method for the detection and extraction of oxolinic acid, flumequine, florfenicol and oxytetracycline from marine sediments was developed and validated. The analytes were extracted from the marine sediment using a solution of oxalic acid diluted in methanol with sonication before detection by HPLC using a diode-array detector (florfenicol and oxytetracycline) and fluorescence (oxolinic acid and flumequine). The quantification limits (QL) were 100 ng/g for oxytetracycline and florfenicol and 5 ng/g for oxolinic acid and flumequine. The coefficients of variation of the repeatability and intermediate precision were less than 10% in all of the analytes. The calibration curves were linear between 50 and 500 ng/ml for oxytetracycline and florfenicol and 1 and 20 ng/ml for oxolinic acid and flumequine. The recuperation rate for the analytes was above 86%.

Salmon aquaculture and antimicrobial resistance in the marine environment.

Antimicrobials used in salmon aquaculture pass into the marine environment. This could have negative impacts on marine environmental biodiversity, and on terrestrial animal and human health as a result of selection for bacteria containing antimicrobial resistance genes. We therefore measured the numbers of culturable bacteria and antimicrobial-resistant bacteria in marine sediments in the Calbuco Archipelago, Chile, over 12-month period at a salmon aquaculture site approximately 20 m from a salmon farm and at a control site 8 km distant without observable aquaculture activities. Three antimicrobials extensively used in Chilean salmon aquaculture (oxytetracycline, oxolinic acid, and florfenicol) were studied. Although none of these antimicrobials was detected in sediments from either site, traces of flumequine, a fluoroquinolone antimicrobial also widely used in Chile, were present in sediments from both sites during this period. There were significant increases in bacterial numbers and antimicrobial-resistant fractions to oxytetracycline, oxolinic acid, and florfenicol in sediments from the aquaculture site compared to those from the control site. Interestingly, there were similar numbers of presumably plasmid-mediated resistance genes for oxytetracycline, oxolinic acid and florfenicol in unselected marine bacteria isolated from both aquaculture and control sites. These preliminary findings in one location may suggest that the current use of large amounts of antimicrobials in Chilean aquaculture has the potential to select for antimicrobial-resistant bacteria in marine sediments.

Analysis of quinolone antibiotics in eggs: preparation and characterization of a raw material for method validation and quality control.

A quality control material for the analysis of quinolone residues in egg samples has been prepared. Homogenized fresh whole egg spiked with nine quinolones (marbofloxacin, norfloxacin, ciprofloxacin, danofloxacin, enrofloxacin, sarafloxacin, difloxacin, oxolinic acid and flumequine), at the concentration level of 500 µg kg(-1) was lyophilized and homogenized to obtain the reference material. The homogeneity of both the bulk and the packed material was verified. Two different strategies, classical and isochronous, were used for the stability study. Conclusions obtained with the classical and isochronous approaches were similar, but the variability of the isochronous results was lower and this led to lower material uncertainty. The reference material was found to be stable for at least 1 year when stored at either room temperature, 4 °C or -20 °C; -80 °C was taken as reference temperature in all cases. The determination of quinolones in eggs was carried out by a previously developed and validated method making use of a pressurized liquid extraction followed by liquid chromatography with fluorescence detection. The suitability of the material prepared was demonstrated by using a lyophilized egg material spiked with nine quinolones as sample in a proficiency test.

Measurement of trace levels of antibiotics in river water using on-line enrichment and triple-quadrupole LC-MS/MS.

This study presents the development of an automated on-line solid phase extraction (SPE)-liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of 23 antibiotics in environmental water samples. After optimisation of LC-MS/MS conditions, SPE parameters such as sorbent type, sample pH or sample volume were optimised. Antibiotic recoveries ranged from 64% to 98% and compared favourably with those achieved using off-line SPE. Limits of detection were in the range 0.5-13.7 ng L(-1). This on-line SPE-LC-MS/MS procedure was applied to the analysis of water samples taken in three rivers within the Seine River basin, near Paris (France). The obtained results revealed the occurrence of 12 antibiotics, including tylosin, erythromycin, tetracycline, amoxicillin, trimethoprim, sulfamethoxazole, oxolinic acid, flumequine, norfloxacin, ciprofloxacin, ofloxacin, and vancomycin (2-1435 ng L(-1)).

Determination of quinolone residues in infant and young children powdered milk combining solid-phase extraction and ultra-performance liquid chromatography-tandem mass spectrometry.

The present work describes a method based on solid-phase extraction (SPE) and ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) for the simultaneous determination of three quinolones (pipemidic acid, oxolinic acid and flumequine) and twelve fluoroquinolones (marbofloxacin, fleroxacin, pefloxacin, levofloxacin, norfloxacin, ciprofloxacin, enrofloxacin, danofloxacin, lomefloxacin, difloxacin, sarafloxacin, and moxifloxacin) in different infant and young children powdered milks. After suitable deproteination of the reconstituted powdered samples, a SPE procedure was developed providing recovery values higher than 84% (RSDs lower than 13%) for all the analytes, with limits of detection between 0.04 and 0.52 µg/kg. UPLC-MS/MS analyses were carried out in less than 10 min. Sixteen infant and young children powdered milk samples of different origin, type and composition bought at Spanish markets were analyzed. Residues of the selected antibiotics were not detected in any of the analyzed samples.

Supramolecular solvents in solid sample microextractions: application to the determination of residues of oxolinic acid and flumequine in fish and shellfish.

Supramolecular solvents are here proposed firstly as extractants in solid sample microextractions. The approach was evaluated by extracting flumequine (FLU) and oxolinic acid (OXO), two widely used veterinary medicines, from fish and shellfish muscle using a supramolecular solvent made up of decanoic acid (DeA) reverse micelles. The antibiotics were extracted in a single step (approximately 15 min), at room temperature, using 400 microL of solvent. After centrifugation, an aliquot of the extract was directly analyzed by liquid chromatography and fluorescence, without the need of clean-up or solvent evaporation. Contrary to the previously reported methods, both OXO and FLU were quantitatively extracted from fish and shellfish, independently of sample composition. The high extraction efficiencies observed for these antibiotics were a consequence of their amphiphilic character which resulted in the formation of DeA-OXO and DeA-FLU mixed aggregates. The quality parameters of this quantitative method including sensitivity, linearity, selectivity, repeatability, trueness, ruggedness, stability, decision limit and detection capability were evaluated according to the 2002/657/EC Commission Decision. Quantitation limits in the different samples analyzed (salmon, sea trout, sea bass, gilt-head bream, megrim and prawns) ranged between 6.5 and 22 microg kg(-1) for OXO and, 5 and 15 microg kg(-1) for FLU. These limits were far below the current maximum residue limits (MRLs) set by the European Union (EU) (i.e. 100 and 600 microg kg(-1), for OXO and FLU, respectively). The trueness of the method was determined by analyzing a Certified Reference Material (CMR, BCR-725) consisting of a lyophilised salmon tissue material. Recoveries for fortified samples (50-100 microg kg(-1) of OXO and 50-600 microg kg(-1) of FLU) and their relative standard deviations were in the intervals 99-102% and 0.2-5%, respectively. The repeatability, expressed as relative standard deviation, was 3.6% for OXO and 2.3% for FLU ([OXO]=[FLU]=200 microg kg(-1) and n=11).

Quantitation and identity confirmation of residues of quinolones in tilapia fillets by LC-ESI-MS-MS QToF.

A method for simultaneous determination of flumequine (FLM), oxolinic acid (OXO), sarafloxacin (SAR), danofloxacin (DAN), enrofloxacin (ENR), and ciprofloxacin (CIP) in tilapia (Orechromis niloticus) fillets, using liquid chromatography-tandem mass spectrometry (LC-ESI-MS-MS QToF) is presented. The quinolones were extracted from the food matrix with a solution of 10% trichloroacetic acid-methanol (80:20 v/v) with ultrasonic assistance. Clean-up of the extract solution was performed by using polymeric solid-phase extraction cartridges. The LC separation was carried out on an octadecyl hybrid silica column (C18, 150 mm x 3 mm, 5 microm). The column temperature was set at 30 degrees C, and gradient elution (0.2 mL min(-1)) was performed using water and acetonitrile, both containing 0.1% of acetic acid, as mobile phase components. The analytes were ionized using electrospray in the positive polarity mode. The following analytical results were obtained: linearity was about 0.99 for all the quinolones; intra and inter-assay precision (RSD%) were lower than 12.7 and 20%, respectively; and recoveries were from 89 to 112%. The quantitation limits were below the maximum residue limits established for the analytes. The method is suitable for the determination of quinolone residues in fish fillets and the QToF technique made it possible to obtain m/z ratios with less than 10 ppm of error for each analyte.

Are liquid chromatography/electrospray tandem quadrupole fragmentation ratios unequivocal confirmation criteria?

Multiple reaction monitoring (MRM) ratios as provided by tandem mass spectrometers are used to confirm positive residue findings (e.g. veterinary drugs or pesticides). The Commission Decision 2002/657/EEC defines tolerance levels for MRM ratios, which are intended to prevent the reporting of false positives. This paper reports findings where blank sample extracts have been spiked by a drug (difloxacin) and the corresponding measured MRM ratios significantly deviated from MRM ratios observed in matrix-free solution. The observation was explained by the formation of two different [M+H](+) analyte ions within the electrospray ionization (ESI) interface. These two ions vary only by the site of analyte protonation. Since they are isobaric, they are equally transmitted through the first quadrupole, but are differently fragmented in the collision chamber. The existence of two isobaric ions was deduced by statistical data and the observation of a doubly charged analyte ion. It was hypothesized that the combined presence of [M+H](+) and [M+2H](2+) implies the existence of two different singly charged ion species differing only by the site of protonation. Low- and high-energy interface-induced fragmentation was performed on the samples. The surviving precursor ion population was mass selected and again fragmented in the collision chamber. Equal product ion spectra would be expected. However, very different product ion spectra were observed for the two interface regimes. This is consistent with the assumption that the two postulated isobaric precursor ions show different stability in the interface. Hence the abundance ratio among the two types of surviving precursor ions will shift and change the resulting product ion spectra. The existence of the postulated singly charged ions with multiple chargeable sites was finally confirmed by successful ion mobility separation.

Degradation of oxolinic acid and flumequine in aquaculture pond waters and sediments.

Oxolinic acid (OA) and flumequine (FLU) are two of the quinolone antibiotics (QAs) that are widely used in aquaculture. The purpose of this study was to understand the fates of OA and FLU in waters and sediment slurries from aquaculture ponds in a laboratory experiment. Waters and sediments were sampled from an eel (Anguilla japonica) pond and a shrimp (Penaeus vannamei) pond. The effects of light, microbial activities, and temperature on the degradation of these two QAs were elucidated. Results indicated that light plays a major role in the degradation of OA and FLU in waters and sediment slurries. Under illuminated and non-sterile conditions, the half-lives (t(1/2)) of OA were 2.3-4.8 and 9.5-15.0 days in the waters and sediment slurries, respectively. For FLU, under the same conditions, t(1/2) values were 1.9-2.3 and 3.6-6.4 days, respectively. Photodegradation of OA and FLU was much faster in water than in sediment slurry. In both environments, degradation became very slow or would plateau after only minimal change in the dark. Besides the effect of light, biodegradation had very minor effects on the degradation of the two QAs in the sediment slurries. The only independent biodegradation was found when OA was placed in shrimp pond sediment slurry, but at a much lower rate (t(1/2) of 98.7 days) than in light. Biodegradation of FLU was also found in the eel pond sediment slurry but only through an additional connection with light. Also, re-addition enhanced the degradation of OA in shrimp pond sediment slurry, but slowed the degradation of FLU in the eel pond sediment slurry in the dark. The temperature experiment in this study showed no significant effects on degradation of the two QAs in either pond waters or sediment slurries.

[Residues of tetracycline and quinolones in wild fish living around a salmon aquaculture center in Chile]. / Residuos de tetraciclina y quinolonas en peces silvestres en una zona costera donde se desarrolla la acuicultura del salmón en Chile.

The presence of residues of tetracycline, quinolones and antiparasitic drugs was investigated in wild fish captured around salmon aquaculture pens in Cochamó, Region X, Chile. Residues of both antibiotics were found in the meta [corrected] of two species of wild fish that are consumed by humans, robalo (Elginops maclovinus) and cabrilla (Sebastes capensis) [corrected] These findings suggest that the antibiotic usage in salmon aquaculture in Chile has nvironmental implications that may affect human and animal health. More studies are needed in Chile to determine the relevance of these findings for human and animal health and the environment to regulate this use of antibiotics.

Residuos de tetraciclina y quinolonas en peces silvestres en una zona costera donde se desarrolla la acuicultura del salmón en Chile / Residues of tetracycline and quinolones in wild fish living around a salmon aquaculture center in Chile

La presencia de antibacterianos y antiparasitarios residuales fue investigada en muestras de carne de peces silvestres de consumo humano pescados alrededor de un recinto de acuicultura en Cochamó (41° 29' S; 72° 19'W), X Región, Chile. Esta investigación demostró que peces silvestres, incluyendo róbalo (Elginops maclovinus), cabrilla (Sebastes capensis) y truchas de vida libre (Oncorhynchus mykiss), ingieren alimento artificial para salmón y que la carne de algunos ejemplares de estos peces contienen tetracicilina y quinolona en cantidades detectables. Estos resultados sugieren que el uso de antibacterianos en la acuicultura del salmón, como ha sido demostrado en otros países, tiene efectos ambientales que se proyectan más allá de los recintos de acuicultura. Se indica que dada la relevancia de estos hallazgos para la salud humana y animal, el ambiente requerirá de estudios más amplios y detallados para implementar futuras regulaciones del uso de antibacterianos en acuicultura.

The presence of residues of tetracycline, quinolones and antiparasitic drugs was investigated in wild fish captured around salmon aquaculture pens in Cochamó, Region X, Chile. Residues of both antibiotics were found in the meta of two species of wild fish that are consumed by humans, robalo (Elginops maclovinus) and cabrilla (Sebastes capensis) . These findings suggest that the antibiotic usage in salmon aquaculture in Chile has environmental implications that may affect human and animal health. More studies are needed in Chile to determine the relevance of these findings for human and animal health and the environment to regulate this use of antibiotics.

Antibiotic resistance in bacteria from shrimp farming in mangrove areas.

Shrimp farming is a sufficiently large and mature industry to have an effective range of antimicrobial agents for most bacterial diseases in shrimp culture. However, at present, there exists great concern over the widespread use of antibiotics in aquaculture, which may result in residue of antibiotics in water and mud, and subsequently, the development of antibiotic resistance in bacteria in the environment. There is limited understanding about the effect of antibiotic residues on bacteria resistance in shrimp farming environment. Therefore, a study was conducted to investigate bacterial resistance to Norfloxacin (NFXC), Oxolinic Acid (OXLA), Trimethoprim (TMP) and Sulfamethoxazole (SMX), which were found in four shrimp farming locations in mangrove areas in Vietnam. Findings indicate that there is a relatively high incidence of bacteria resistance to these antibiotics observed in most of the studied sites, particularly to antibiotics with concentration of 0.1 microg/ml. Yet the relation between concentration of antibiotic residues and incidence of antibiotic resistance is not clearly defined. Among individual antibiotics, the incidence of resistance to TMP and SMX was higher than the others. Identification of bacteria isolated from mud samples by DNA analyzer shows that Bacillus and Vibrio are predominant among bacteria resistant to the antibiotics. The result of the study also indicates that these antibiotics in media degraded more rapidly due to the presence of resistant bacteria.

Multiresidue method for simultaneous determination of ten quinolone antibacterial residues in multimatrix/multispecies animal tissues by liquid chromatography with fluorescence detection: single laboratory validation study.

Quinolone antibacterials are veterinary drugs authorized for use in food animal production. The analysis of residual amounts of drugs in food from animal origin is important for quality control of products for consumers. For this purpose, Maximum Residue Limits (MRLs) have been set up by a European Union Council Regulation on Veterinary Drug Residues (No. 90/2377/EEC and subsequent), and 8 quinolones received MRLs at concentration levels depending on both the matrix and the animal species of interest. A method was developed for screening and confirming 10 quinolone residues (ciprofloxacin, danofloxacin, difloxacin, enrofloxacin, flumequine, marbofloxacin, nalidixic acid, norfloxacin, oxolinic acid, sarafloxacin) in a wide variety of matrixes of different animal species. It involves extraction of the residues from the biological tissues/fluids by acidic aqueous solution, centrifugation and filtration prior to injection on a C18 narrow-bore column, and detection through a 3-step-mode fluorescence detector. The method was validated during a 2-week study for a set of 8 species-matrixes (i.e., bovine raw milk, bovine muscle, porcine muscle, porcine kidney, porcine liver, fish flesh and skin, poultry muscle, whole egg). Residues were quantified down to 15 microg/kg with limits of detection and quantitation ranging from 4 to 11 and 13 to 36 microg/kg, respectively, which are sufficient compared to the wide range of MRLs set for these substances (from 30 microg/kg for danofloxacin in milk to 1900 microg/kg for difloxacin in poultry liver). The limit of performance of the method in terms of CCalpha and CCbeta, the critical concentrations stated in the Decision No. 2002/657/EC and the ISO Standard No. 11843, has been calculated for the authorized (MRL) substances but only estimated in the case of the nonauthorized (non-MRL) substances.

Micellar electrokinetic chromatography for determination of drug partition in phospholipids.

The lipophilicity of pipemidic, nalidixic and oxolinic acids was determined by forming phospholipidic micelles directly in an electrophoretic capillary. Phosphatidylcholine derivatives, namely L-alpha-dilauroyl phosphatidylcholine (DLPC) or L-alpha-dimiristoyl phosphatidylcholine (DMPC), were added in the run buffer (50 mM phosphate buffer at pH 7.4). To obtain a mixed micelle, phospholipidic derivatives and sodium cholate were together added in the run buffer. Considering the increasing of migration time when phosphatidylcholine derivative is added in the run buffer, Ks can be determined and then quinolones lipophilicity.

Multiresidue determination of eleven quinolones in milk by liquid chromatography with fluorescence detection.

A liquid chromatographic method with fluorescence detection was developed for simultaneous determination of norfloxacin, ofloxacin, ciprofloxacin, pefloxacin, lomefloxacin, danofloxacin, enrofloxacin, sarafloxacin, difloxacin, oxolinic acid, and flumequine in milk The samples were extracted with 10% trichloroacetic acid/acetonitrile (9 + 1, v/v) and cleaned by Strata-X reversed-phase solid-phase extraction cartridges. The 11 quinolones were separated on a reversed-phase C18 column (Hypersil BDS-C18) with mobile phase gradient elution and detected with fluorescence by means of a wavelength program. The recoveries for milk fortified with the 11 quinolones at 3 levels were 69-88% with acceptable relative standard deviations of <9% (intraday) and <14% (interday). The limits of detection were 23 microg/L for enrofloxacin, and 1-9 microg/L for the other 10 quinolones.