No abstract

This study was performed in order to determine the stability of antibiotics belonging to eight families in solution or biological matrix. Knowledge of the stability of antibiotics has to be demonstrated during method development or validation. The stability of stock standard solutions of 53 antibiotics was assessed after determining the appropriate conditions of dissolution and storage. The stability of the same 53 antibiotics after addition to negative control cow milk or pork muscle tissue stored at -18 and -70 degrees C was also assessed. Our concern was to obtain information concerning the stability of antibiotic residues in fortified biological matrixes in order to make easier the implementation of a routine screening method for antibiotic residues within the framework of the French monitoring program. Antibiotic solutions and fortified samples were analyzed using an LC/MS/MS method previously validated for screening purposes and for which it was checked that all pertinent criteria to obtain interpretable stability results were fulfilled. The design for testing the stability of antibiotics in solutions and matrix samples is described, as well as the rules of decision that were observed. Term periods for the stability study ranged from 1 month to 1 year, depending on the class of compounds. The results presented in this article will be useful and time-saving for many reference and field laboratories because LC/MS/MS methods are more and more commonly used for screening purposes.

Premi Test contains viable spores of a strain of Bacillus stearothermophilus which is sensitive to antimicrobial residues, such as beta-lactams, tetracyclines, macrolides and sulphonamides. The growth of the strain is inhibited by the presence of antimicrobial residues in muscle tissue samples. Premi Test was validated according to AFNOR rules (French Association for Normalisation). The AFNOR validation was based on the comparison of reference methods (French Official method, i.e. four plate test (FPT) and the STAR protocol (five plate test)) with the alternative method (Premi Test). A preliminary study was conducted in an expert laboratory (Community Reference Laboratory, CRL) on both spiked and incurred samples (field samples). Several method performance criteria (sensitivity, specificity, relative accuracy) were estimated and are discussed, in addition to detection capabilities. Adequate agreement was found between the alternative method and the reference methods. However, Premi Test was more sensitive to beta-lactams and sulphonamides than the FPT. Subsequently, a collaborative study with 11 laboratories was organised by the CRL. Blank and spiked meat juice samples were sent to participants. The expert laboratory (CRL) statistically analysed the results. It was concluded that Premi Test could be used for the routine determination of antimicrobial residues in muscle of different animal origin with acceptable analytical performance. The detection capabilities of Premi Test for beta-lactams (amoxicillin, ceftiofur), one macrolide (tylosin) and tetracycline were at the level of the respective maximum residue limits (MRL) in muscle samples or even lower.

A high-performance liquid chromatographic (HPLC) method for the simultaneous determination of tilmicosin, tylosin, spiramycin, and its major metabolite neospiramycin was developed that is suitable for porcine, bovine, and poultry muscles. Macrolide residues were extracted from muscle with acetonitrile, fat was removed by liquid-liquid extraction with isooctane, and the extract was then cleaned on Bond Elut C18 cartridges. The HPLC separation was performed on an Inertsil ODS3 C18 column (150 × 4 mm) with 0.05% trifluoroacetic acid-acetonitrile in a gradient mode. Two different chromatographic gradients were used for tilmicosin-tylosin and spiramycin-neospiramycin, and the detection wavelengths were 287 and 232 nm, respectively. The method was validated from ½ the maximum residue limit (MRL) to 4 times the MRL with pork muscle samples. Mean recoveries were 60, 63.5, 51, and 42% for tilmicosin, tylosin, spiramycin, and neospiramycin, respectively. The detection limits are 15 μg/kg for tilmicosin and tylosin, 30 μg/kg for spiramycin, and 25 μg/kg for neospiramycin. Linearity, precision, and accuracy of the method were also tested.

A high-performance thin-layer chromatographic method based on solid-phase extraction has been developed for the qualitative determination of seven quinolones (enrofloxacin, ciprofloxacin, danofloxacin, norfloxacin, flumequine, oxolinic acid and nalidixic acid) in pork muscle. After preparation of the samples by extraction and clean-up by solid-phase extraction on reversed-phase cartridges, extracts were spotted and eluted on silica gel plates. The plate is first inspected under UV illumination at 312 nm, then sprayed with terbium chloride solution and again monitored under 312 nm UV. The method has been validated to a level of 15 lag kg -1 for enrofloxacin, ciprofloxacin, danofloxacin, norfloxacin and 5 lag kg -I for flumequin, oxolinic acid and nalidixic acid.