Analysis of fluoroquinolones in animal feeds by liquid chromatography with fluorescence detection.

An analytical method for the analysis of six fluoroquinolones (FQs) in animal feeds was developed. The sample treatment consists of a simple and rapid extraction of the analytes by manual shaking with an acetonitrile-water mixture containing hydrochloric acid without further sample cleanup. Matrix effects were minimized by diluting the extract with water. Determination was carried out by liquid chromatography using fluorimetric detection. The method was validated in-house in four different feed matrices (poultry, cow, pig, and lamb feed). Mean recoveries ranging from 80 to 105%, with relative standard deviations below 12%, were achieved from spiked animal feed samples on the 0.2-2.0 µg/g level. No relevant differences were observed between the studied feeds, this ensuring that the method was reliable for a wide variety of feed matrices. Decision limit and detection capability values are below 0.08 and 0.13 mg/kg, respectively, for most FQs. The results obtained demonstrate the feasibility of the analytical method developed for a routine use to control the illegal use of these substances in feeding stuffs.

Analysis of macrolide antibiotics in river water by solid-phase extraction and liquid chromatography-mass spectrometry.

A liquid chromatography-mass spectrometry (LC-MS) method was developed for the determination of five macrolides in natural water samples, using kitasamycin as surrogate. The macrolides were extracted from water samples using Oasis HLB cartridges. Pre-concentration factors up to 250 were obtained. Separation was carried out in an end-capped silica-based C18 column and mobile phases consisting of water/acetonitrile mixtures containing ammonium acetate. Detection was performed by mass spectrometry with a single quadrupole and a triple quadrupole using an electrospray interface. The quality parameters obtained with these two approaches were compared. The detection limits of the whole process were about 1 ng l(-1). The recoveries from 250 ml of water samples spiked at 25-125 ng l(-1) level were in the range 85-115%, except for azithromycin levels, which were around 70%. Erythromycin-H2O, clarithromycin and azithromyzin were found, at the sub ng l(-1) level, in the studied rivers.

Determination of triorganotin species in water samples by liquid chromatography-electrospray-mass spectrometry.

Liquid chromatography coupled to electrospray-mass spectrometry (LC-ES-MS) with positive ion detection was evaluated for the determination of tributyltin and triphenyltin in water samples using tripropyltin as internal standard. The separation was performed in the isocratic mode on a silica-based C18 column with a mobile phase containing 0.02% trifluoroacetic acid in acetonitrile-water (50:50, v/v). The optimum LC-ES-MS conditions were established and quantification was performed on the basis of the [M]+ ions. Limits of detection for standard solutions were 100 and 200 pg Sn injected for triphenyltin and tributyltin, respectively, and good reproducibility was observed. Solid-phase extraction was carried out on C18 cartridges to preconcentrate the analytes from natural water samples, with recoveries ranging from 80 to 110%. Limits of detection for SPE-LC-ES-MS were in the range of low ng l(-1), which demonstrates the suitability of the method for environmental samples.