Ion Separation in Air Using a Three-Dimensional Printed Ion Mobility Spectrometer

The performance of a small, plastic drift tube ion mobility spectrometer (DT-IMS) is described. The IMS was manufactured using three-dimensional (3D) printing techniques and operates in the open air at ambient pressure, temperature, and humidity. The IMS housing and electrodes were printed from nonconductive polylactic acid (PLA, housing) and conductive polyethylene terephthalate glycol-modified polymer containing multiwalled carbon nanotubes (PETG-CNT, electrodes). Ring electrodes consisting of both an inner disk and an outer ring were used to prevent neutral transmission while maximizing ion transmission. As a stand-alone instrument, the 3D printed IMS is shown to achieve resolving powers of between 24 and 50 in positive ion mode using tetraalkylammonium bromide salts (TAA), benzylamines (mono-, di-, and tri-), and illicit drugs (MA, MDEA, and haloperidol). Resolving powers of between 29 and 42 were achieved in negative ion mode using sodium alkyl sulfates (C8, C12, C16, and C18). Reduced ion mobilities of TAA cations (C2–C8) were calculated at 14% relative humidity in air to be 1.36, 1.18, 1.03, 0.90, 0.80, 0.73, and 0.67, respectively. The effect of humidity on reduced ion mobilities of TAA cations is discussed. 3D printing is shown to be a quick and cost-effective way to produce small IMS instruments that can compete in performance with conventionally manufactured IMS instruments that also operate in the open air. An important difference between this IMS and other instruments is the absence of a counter gas flow.