الفهرس 
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Abstract
A total of 75 beef and chicken tissues samples, distributed as 20 imported frozen beef and 10 imported frozen cattle livers samples (represented several meat - exporting foreign countries) , besides locally – manufactured meat products consisted of 10 samples each of beef luncheon and canned beef, plus 5 samples of pastirma (dried and cured beef) (represented many Egyptian meat plants) purchased from shops and groceries, in addition to 20 chicken breast samples taken form correspondent number of locally – reared birds after being slaughtered and dressed at different Egyptian poultry shops. Beef, its products and livers samples were investigated for zeranol (synthetic growth promoter having estrogenic activity) residues, whereas chicken breast samples analyzed for some, common antimicrobials residues. Qualitative and quantitative detection of all beef and chicken tissues residues were performed by using a validated liquid chromatography coupled with a tendem mass spectrometry (LC – MS / MS) technique. Our findings declared absence of zeranol residues in imported frozen beef and cattle livers samples as well as in locally – manufactured beef luncheon, canned beef, and pastirma (dried & cured beef) samples that derived from the imported frozen beef. Also, neither chloramphenicol, penicillin, nor tetracycline residues could be detected in tested chicken breast samples. Whereas, the residues of florfenicol were recognized in 7 (35%), of sulphaquinoxaline in 3 (15%), and of tylosin in 15 (75%) of such chicken samples. The lowest quantities of the determined antimicrobials residues (florfenicol -sulphaquinoxaline - tylosin) were 0.032, 1.101, and 0.696 micrograms per each kilogram of chicken breast samples (g / kg = ppb) , meanwhile, the highest levels for the same antimicrobials residues were 2.363, 3.090 and 8.160 g/kg, respectively. By comparison, non of the quantified antimicrobials residues levels was exceeded the maximum residue limit (MRL) that recommended by several regulatory agencies as 100 g/ kg for each antimicrobial residue.