Simultaneous determination of 10 β2-agonists in swine urine using liquid chromatography–tandem mass spectrometry and multi-walled carbon nanotubes as a reversed dispersive solid phase extraction sorbent

A simple and inexpensive pretreatment procedure was developed for 10 β2-agonists (clenbuterol, ractopamine, salbutamol, bambuterol, penbuterol, tulobuterol, clorprenaline, mabuterol, cimaterol and terbutaline) in swine urine using dispersive solid phase extraction (dSPE) with multi-walled carbon nanotubes (MWCNTs). The sample was analysed after purification by ultra high performance liquid chromatography–positive electrospray ionisation tandem mass spectrometry (UHPLC-ESI–MS/MS). The pH value of the swine urine, extraction time, type and amount of MWCNTs and type of eluent were optimised to increase the sample throughput and sensitivity. The samples were quantified using clenbuterol-D9, ractopamine-D6 and salbutamol-D3 as internal standards. The recoveries of the target compounds from swine urine samples at pH 10.0 were most efficient when using 20 mg of MWCNTs with a 30–50 nm outer diameter and a length of 10–30 μm, while a mixture of water/methanol (90:10, v/v) with 0.5% formic acid was shown to be the most suitable solvent for desorbing the compounds from the MWCNTs. The proposed method was validated according to the European Commission Decision 2002/657/EC, which determines linearity, specificity, decision limit (CCα), detection capability (CCβ), recovery, precision and stability.