Lincosamides methods

For efficient extraction of macrolide and lincosamide residues from edible animal products, bound residues should be rendered soluble, most if not all of the proteins should be removed, and high recoveries for all analytes should be provided. Since tliese antibiotics do not strongly bind to proteins, many effective extraction methods have been reported. Sample extraction/deproteinization is usually accomplished by vortexing liquid samples or homogenizing semisolid samples with acetonitrile (136—139), acidified (136,140-142) orbasified acetonitrile (143), methanol (14, 144, 145), acidified (145-147) or basified methanol (148), chloroform (149-151), or dichloromethane under alkaline conditions (152). However, for extraction of sedecamycin, a neutral macrolide antibiotic, from swine tissues, use of ethyl acetate at acidic conditions has been suggested (153), while for lincomycin analysis in fish tissues, acidic buffer extraction followed by sodium tungstate deproteinization has been proposed (154). 

At present, methods based on liquid chromatography are most widely used for determining macrolides and lincosamides in biological samples (Fig. 29.4). 

Electrochemical detection is better suited to the analysis of erythromycin and lincomycin. This method of detection has been applied for the determination of erythromycin A (139) and lincomycin (154) residues in salmon tissues. Liquid chromatography coupled with mass spectrometry is particularly suitable for confirmatory analysis of the nonvolatile macrolides and lincosamides. Typical applications of this technique are through thermospray mass spectrometry, which has been used to monitor pirlimycin in bovine milk and liver (141,142), and chemical ionization, which has been applied for identification of tilmicosin (151) in bovine muscle, and for identification of spiramycin, tylosin, tilmicosin, erythromycin, and josamycin residues in the same tissue (150). 

Table 29.4 Physicochemical Methods for Macrolide and Lincosamide Antibacterials in Edible Animal Products... 

In 2008, Carretero et al. described a multi-class method for the analysis of 31 antibacterials (including f)-lactams, macrolides, lincosamides, quinolones, sulfonamides, tetracyclines, nitroimidazoles, and trimethoprim) in meat samples by PLE-LC-MS/MS. Meat samples were homogenized and blended with EDTA-washed sand, then extracted with water by applying 1500 psi (Ib/in. ), at 70°C. One extraction cycle was 10 min. A drawback of the method is the large volumes of extracts (40 ml) obtained, which required evaporation to concentrate the extract volume prior to final analysis. This evaporation step considerably increases the time required for sample preparation. The proposed method has been applied to the analysis of 152 samples of cattle and pig tissues, with the presence of quinolones, tetracyclines, and sulfonamides detected in 15% of the samples, although at concentrations below the MRLs. 

A high-throughput method that combines on-line extraction and determination by LC-MS/MS has been developed for the screening of 13 multi-class antibacterials (macrolides, fluoroquinolones, lincosamides, and trimethoprim) in different animal muscle tissues. After sample deproteinization with acetontirile, the extracts were directly loaded onto the SPE cartridge, packed with an Oasis HLB... 

As a result of these observations, recommendations have been made to include an incubation step in methods of analysis for lincosamides in liver. " If the aim is to detect lincosamide use, then inclusion of an incubation step is necessary to maximize the possibility of detection. However, as indicated earlier, MRLs, where set, are based on the parent compound only with no reference to the metabolites, either by summation of separate measurements or by conversion to a suitable marker. Thus, inclusion of an incubation step could lead to falsely high residue concentrations and the possibility of samples that fall within the legal limits being reported as non-compliant. As a result, analytically, steps should be taken to minimize enzymatic activity to prevent this reverse metabolism. A long-term solution to this issue might be to include the sulfoxides in the legislation as additional markers in some form. 

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