Dramatic signal reduction in ion-mobility spectrometry by residues of solvents

During our evaluation of ion-mobility spectrometry (IMS) screening for the abuse of the beta-agonist clenbuterol during fattening in cattle, we found that clenbuterol could not be detected with the instrument in extracts obtained by solid-phase extraction or ion-pair extraction, although the recovery for these procedures was at least 85%. Several experiments showed that the signal loss occurred mainly during the evaporation of the organic solvent. Again, it could be shown that no clenbuterol was lost during this step. On further investigation, we found that so-called solvent residues, which are left after the evaporation of the organic solvent, caused a significant reduction of the clenbuterol signal. Other reagents used in our sample pretreatment procedures were also found to reduce the signal. For example, the signal reductions caused by the different reagents used for the ion-pair extraction of clenbuterol from human urine were determined. We think that IMS is only useful for our purpose if a chromatographic preseparation is performed.