Reliability of ion mobility spectrometry for qualitative analysis of complex, multicomponent illicit drug samples

Ion mobility spectrometry (IMS) has been used for trace analysis of illicit drugs, but it can also provide reliable qualitative analysis of bulk forensic drug items, despite the complexity of these samples. The drug/drug and drug/excipient combinations representing over 80% of the samples reported by state and federal forensic laboratories over the past 7 years were compiled from reports of the National Forensic Laboratory Information System (NFLIS). From this set of materials, IMS detection windows were set for eight controlled substances, including methamphetamine, 3,4-methylenedioxymethamphetamine hydrochloride (MDMA), cocaine, heroin, fentanyl, hydrocodone, oxycodone, and alprazolam. The reduced mobilities of the eight controlled substances were measured over an extended period of time to determine variability with respect to the size of the detection windows. Uncertainties in reduced mobilities smaller than 0.001 cm2 V−1 s−1 were obtained, and detection windows were set to between ±0.003 and ± 0.005 cm2 V−1 s−1. Reduced mobilities are instrument and operating condition dependent, and must be determined for each instrument. Peak overlaps are observed in the drug/drug combinations, but at least one controlled substance can be detected in each mixture. Excipient concentrations must be quite high (>75 wt%) in binary mixtures to interfere with the detection of the controlled substance. IMS can be used to identify many of the excipients, and can detect multiple (for these samples, as many as 4) substances in complex samples. Over-the-counter (OTC) tablet medications for cold, flu, and allergy relief can be distinguished from tablets containing controlled substances. Bulk materials, including tablets, are sampled simply by using a fine probe to restrict the amount of material transferred to the IMS substrate. IMS represents a distinct advantage over color tests for field analysis of illicit drugs, except in the case of cannabis/THC samples.