Development of rapid methodologies for the isolation and quantitation of drug metabolites by differential mobility spectrometry - mass spectrometry

Abstract

Clinical and forensic toxicology laboratories are inundated with thousands of samples requiring lengthy chromatographic separations prior to mass spectrometry. Here, we employ differential mobility spectrometry (DMS) interfaced to nano-electrospray ionization-mass spectrometry to provide a rapid ion filtration technique for the separation of ions in gas phase media prior to mass spectral analysis on a DMS-integrated AB SCIEX API 3000 triple-quadrupole mass spectrometer. DMS is efficient at the rapid separation of ions under ambient conditions and provides many advantages when used as an ion filtration technique in tandem with mass spectrometry (MS) and MS/MS. Our studies evaluated DMS-MS/MS as a rapid, quantitative platform for the analysis of drug metabolites isolated from urine samples. In targeted applications, five metabolites of common drugs of abuse were effectively and rapidly separated using isopropanol and ethyl acetate as transport gas modifiers, eliminating the gas chromatography or liquid chromatography-based separations commonly employed in clinical and forensic toxicology laboratories. Calibration curves were prepared for the selected drug metabolites utilizing deuterated internal standards for quantitative purposes. The feasibility of separating and quantitating drug metabolites in a rapid fashion was evaluated by compensation voltage stepping followed by multiple reaction monitoring (MRM) detection. Rapid profiling of clinical and forensic toxicology samples could help to address an urgent need within the scientific community by developing high-throughput analytical methodologies, which could reduce significant case backlogs present within these laboratories.

Keywords: DMS; DMS-MS; Differential mobility spectrometry - mass spectrometry; Drug metabolites; FAIMS; Rapid quantitation; Rapid separation; Toxicology.

Fig. 1

Five metabolites investigated by DMS-MS/MS for the development of rapid quantitative methods

Fig. 2

CV peak position plots for BE (left) and 6-AM (right) as a function of five applied separation voltages (SV) in the presence of 2.2 % IPA modifier introduced into the curtain gas

Fig. 3

Compensation voltage peak position plot for BE and 6-AM as a function of five applied separation voltages in the presence of 2.2 % IPA modifier introduced into the curtain gas

Fig. 4

Peak position plot demonstrating the effects of EtOAc modifier concentration on the separation of BE and 6 AM at a curtain gas temperature of 170 °C. Separation voltage (SV) is represented on the x-axis (top) and compensation voltage (CV) is represented on the y-axis

Fig. 5

DMS-MS/MS separation of five metabolites of common drugs of abuse with IPA as a modifier

Fig. 6

Seven point calibration curve for BE with BE-d3 as an internal standard. The linear dynamic range of the quantitative DMS-MS/MS method was 100 pg to 10 ng