Analysis of 19-nortestosterone residue in animal tissues by ion-trap gas chromatography-tandem mass spectrometry

A rapid sample treatment procedure for the gas chromatography-tandem mass spectrometry (GC-MS) determination of 19-nortestosterone (19-NT) in animal tissues has been developed.In our optimized procedures,enzymatic hydrolysis with β-glucuronidase from Escherichia coli was performed in an acetate buffer (pH 5.2,0.2 mol/L).Next,the homogenate was mixed with methanol and heated at 60 ℃ for 15 min,then placed in an ice-bath at 18 ℃ for 2 h.After liquid-liquid extraction with n-hexane,the analytes were subjected to a normal-phase solid phase extraction (SPE) C18 cartridge for clean-up.The dried organic extracts were derivatized with heptafluorobutyric anhydride (HFBA),and then the products were injected into GC-MS.Using electron impact mass spectrometry (EI-MS) with positive chemical ionization (PCI),four diagnostic ions (m/z 666,453,318,and 306) were determined.A standard calibration curve over the concentration range of 1-20 ng/g was reached,with Y=467084X-68354 (R2 =0.9997) for 19-NT,and the detection limit was 0.3 ng.When applied to spiked samples collected from bovine and ovine,the recoveries ranged from 63% to 101% with relative standard deviation (RSD) between 2.7% and 8.9%.The procedure is a highly efficient,sensitive,and more economical method which offers considerable potential to resolve cases of suspected nandrolone doping in husbandry animals.