Use of molecularly imprinted solid-phase extraction for the selective clean-up of clenbuterol from calf urine

A feasibility study was performed in order to study the possibilities in using molecularly imprinted polymers (MIPs) as sorbent material in solid-phase extraction (MISPE) for clean-up of clenbuterol from urine. A binding study of clenbuterol in several solvents was performed on a clenbuterol imprinted polymer as well as on a blank polymer. These binding experiments were used to find suitable loading, washing and elution solvents for the MISPE procedure. Extraction of clenbuterol from calf urine was performed by directly loading a 10-ml urine sample onto the MIP column. Thereafter the column was washed with 10 ml of acetonitrile containing 1% acetic acid, and finally clenbuterol was eluted with 6 ml of methanol containing 10% acetic acid. A recovery of 65% was obtained. This recovery could be increased up to 75% if a sample volume of 1 ml was used or up to 100% if urine was freeze-dried and the residue was dissolved in acetonitrile and spiked with clenbuterol prior to analysis. Chromatograms of the wash and eluate solutions show an efficient clean-up, which supports the potential of MISPE for clean-up of trace amounts of clenbuterol from calf urine.