Abstract:

A pre-treatment method was developed for determining residual clenbuterol in pork by ELISA and GC-MS. Samples were extracted with ethyl acetate under basic condition, and the extracts were further extracted using diluted hydrochloric acid to remove fat. The hydrochloric acid extracts were re-extracted using ethyl acetate following pH adjustment, and the final extract obtained was divided into two equal parts and each of them was dried by nitrogen blow. Water was added to one part prior to ELISA determination. After derivatization with bis(trimethylsilyl)trifluoroacetamide (BSTFA) another part was detected by GC-MS in selected ion monitoring mode (selected ions: 86, 212, 262, 277) and quantitatively analyzed by external standard method. The GC-MS detection limit was 0.30 μg/kg. The recoveries for clenbuterol determined by ELISA in pork spiked at the levels of 1.0 －5.0 μg/kg were 72.1%－105.6%, and by GC-MS 79.1%－95.7%, and the intra-day relative standard deviations for ELISA and GC-MS determination were 12.5%－ 16.8% and 4.6%－ 6.9%, respectively. There was a good linear correlation (the calibration coefficient was above 0. 999) between peak area and concentration of clenbuterol derivative in the range of 0.005 to 1.000 mg/L.

Key words: pork, ELISA, gas chromatography-mass spectrometry, clenbuterol, residue