Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/8/2006
Publication Date: 3/31/2006
Citation: Chen, G., Smith, E., Qin, F., Liu, L.S. 2006. Time-resolved luminesence screening of antibiotics in tissue matrices without centrifugation and filtration. Journal of Agricultural and Food Chemistry. 54:3225-3230. Interpretive Summary: The presence of antibiotic residues in foods of animal origin is a health concern. Animal tissues are complex and rich in protein and fat, analysis of trace amount of residues typically requires elaborate extraction, enrichment and cleanup, including laborious centrifugation and filtration. To simplify sample preparation we carried out extraction, enrichment, cleanup and time-resolved luminescence measurement directly on a small, glass-back sorbent layer. This method is now successfully applied to antibiotic assay in animal tissue matrices, demonstrated by oxytetracycline screening in catfish muscle at 2 parts per million, the FDA regulatory tolerance level. With measurement directly performed on sorbent surface centrifugation and filtration becomes unnecessary, throughput is therefore improved and costs saved. Furthermore, organic solvent is not needed since both extraction and cleanup are performed in water, providing a friendly method for both analysts and the environment.
Technical Abstract: Analysis of antibiotic residues in foods of animal origin requires multi-step sample preparation including homogenization, extraction, enrichment and cleanup. For spectrometric analysis tissue particulates must be excluded by centrifugation and filtration to minimize scattering and attenuation. We developed earlier a methodology that hyphenates sorbent extraction and solid-matrix time-resolved luminescence (SMTRL). Its application is extended to animal tissues, illustrated by oxytetracycline (OTC) screening in catfish muscle. After homogenization in an EDTA solution, three 10x6 mm glass-back C18 strips are immersed in the homogenate for 20-min for OTC extraction and enrichment. Following cleanup by a 3-min water immersion and an gentle water spray, the strips are dipped into a TRL reagent solution and desiccated. TRL is then measured directly on the sorbent surface. A good linearity (r2 = 0.9966) was obtained in a 0-4 µg/g OTC range with a typical 10-20% RSD. To screen OTC at 2 µg/g, the FDA regulatory tolerance level, a threshold was set at mean -3SD, of TRL signals from 15 samples fortified at 2 µg/g. The results from 33 blind samples included 3 false positives and zero negative. By eliminating centrifugation and filtration, equipment and labor costs are saved, sample throughput improved, and makes field assay possible using a portable fluorometer. Since no organic solvent is needed for extraction and cleanup this method is friendly to both analysts and the environment.