Removal of Interferences and Easier Metabolite Detection by Ion Mobility Mass Spectrometry

Abstract

The task of identifying drug metabolites from complex biological matrices such as bile, plasma, feces, and urine with traditional techniques can be difficult. One of the typical problems when running in vivo samples is that without the use of radiolabeled compounds, there are no reference points to look for xenobiotics. Therefore in the vast majority of cases, the analyst relies heavily upon personal experience and customized analytical strategies to detect and identify low-level metabolites from high endogenous backgrounds. The complexity of this analysis could be significantly reduced by the use of an additional stage of separation, which is orthogonal to the LC and mass spectrometric separations, and occurs on a timescale that is intermediate between the two. A technique that possesses this capability is ion mobility spectrometry (IMS). IMS separates ionic species as they drift through a gas under the influence of an electric field. For any particular ion, the rate of drift depends on its mobility, which in turn is dependent on factors such as mass, charge state and the interaction cross-section of the ion with the gas. This additional dimension of separation fidelity leads to improved specificity and sample definition so that more information about the sample can be extracted. The multidimensional data produced by the Waters® Synapt™ High Definition MS™ (HDMS™) system is visualized and manipulated using DriftScope™ Mobility Environment software. In this work, UPLC®/IMS-TOF-MS (Figure 1) analysis was conducted on a rat bile sample. By using the DriftScope software, the metabolites from this complex matrix were easily visualized, as the drift time was used to separate background ions from real drug-related metabolites. Further extracted ion chromatograms were also obtained by selecting specific ions with the software. As a result, the extracted ion chromatogram and MS spectrum for each metabolite were attained without interference from the endogenous compounds. Experimental The in vivo ketotifen sample was obtained from rat bile. The drug was dosed intraperitonally at 10 mg/kg and bile was collected from 0 to 3 hours after drug administration. The sample was diluted 1/10 using water with 0.1 % formic acid prior to the UPLC/MS analysis. UPLC conditions