RESUMO
Two extraction/clean-up analytical procedures were investigated and compared regarding their recovery and matrix-purification efficiency for screening beta2-agonist residues in fortified bovine urine by high-resolution gas chromatography-mass spectrometry (GC-MS). The first procedure, based on an analytical method originally developed for detecting anabolic steroids, consists of the employment of the nonionic resin, Amberlite XAD-2, a styrene-divinylbenzene copolymer for solid-phase extraction (SPE), followed by liquid-liquid extraction with diethyl ether. The second focuses on the use of a mixed SPE cartridge (reversed-phase and ion-exchange sorbent, Bond Elut Certify). In both cases, the trimethylsilylated derivatives were analyzed by GC-MS with an ion-trap detector. Clenbuterol, salbutamol, and terbutaline were used to spike urine samples during the comparison experimental phase. Afterwards, tulobuterol, mabuterol, mapenterol, cimbuterol, and brombuterol were included in the evaluation of the second procedure (the Bond Elut Certify procedure). At this stage, the detection was accomplished by GC-MS (quadrupole mass analyzer) with selective ion monitoring acquisition. The isotopic dilution method with the hexadeuterated analogues of clenbuterol and salbutamol was applied to prepare calibration curves and calculate recovery percentages. With XAD-2 resin, terbutaline and salbutamol (resorcinol and phenol-type beta2-agonists, respectively) could not be detected at 20 ng/mL or at 40 ng/mL. In spite of clenbuterol having been detected at 20 ng/mL, the results obtained were not reproducible. The use of the reversed-phase and ion-exchange sorbent Bond Elut Certify allowed multiresidue detection and showed several advantages for the screening of clenbuterol such as higher recoveries, cleaner final extracts, reduced sample preparation time, less labor intensive, and easier solvent consumption and disposal. Recoveries over 88% (concentrations ranging from 0.5 to 10 ppb) and limits of detection equal to 0.5 ppb were met for all the beta2-agonists studied with the last method.