Ion mobility spectrometers (IMSs) [1,2] are robust, fast, and sensitive analytical instruments for the detection of explosives [3,4], chemical warfare agents [5], and illicit drugs [6], [7], [8], [9]. The most common IMS is the drift tube ion mobility spectrometer consisting of an ionization source, a drift tube, and a Faraday plate detector [10,11]. The ion source produces charged species using electrospray ionization [12], [13], [14], corona discharge [15], dielectric barrier discharge, and radioactive ionization sources including 63Ni, 3H, and 241Am [16,17]. Because of the speed, sensitivity, and ease of use, IMS has been applied to many fields including food safety analysis, environmental monitoring, and clinical testing [18,19].

The working principle of the drift tube ion mobility spectrometer has three main steps [18,19]. First, the ionization sources generate reactant ions and interact with neutral gaseous sample molecules. The product ions in this chemical ionization process are then guided toward the ion gate by electric fields. The ion gate then opens briefly to allow a thin packet of ions to enter the drift region by lowering the electrical potential applied to the gate electrode. Next, the injected ions then collide with the neutral drift gas molecules while traversing to the detector guided by a linear potential; they have different velocities because of different ion-neutral collision cross-sections. Finally, The ions exit the drift tube and discharge at the Faraday plate detector to produce pico-amps of current. The ion signal is then amplified and recorded to obtain the ion mobility spectrum for qualitative and quantitative analyses.

For the ionization, separation, and detection of ions are all conducted under atmospheric conditions, the IMS instruments are much simpler and cheaper than their mass spectrometer counterparts [2]. Nevertheless, for the ionization process under atmosphere conditions, the ionization competes between various molecules with different ionization tendencies when complex samples are introduced to the ionization source; thus, the ion intensity may be affected by many factors, resulting in deteriorated quantitative results to reflect the composition of molecules in the sample. To address this issue, front-end separation techniques such as gas chromatography (GC) [20,21], liquid chromatography(LC) [22], [23], [24], [25], and electrophoresis have been employed in an ion mobility spectrometer prior to ionization. The front separation greatly simplifies the ion chemistry for ion mobility spectrometry and thus enhances the quantitative analysis performance as well as qualitative results. For the separation mechanisms of ion mobility spectrometry and chromatography separations are orthogonal, the peak capacity of this two-dimensional analysis is significantly improved. For these advantages, the application of GC-IMS has greatly expanded to foodstuffs, environment analysis, clinical testing, forensic analysis, and exhaled breath analysis in recent years [4,[26], [27], [28], [29], [30], [31], [32]].

Another concern about ion mobility spectrometry is the resolving power and sensitivity [11,33,34]. Generally, the drift tube ion mobility spectrometer uses a signal-averaging method for data acquisition to improve the signal-to-noise ratio of the spectrum by collecting and averaging tens of individual ion mobility spectra. Real signals are constant with random noise. After averaging, the noises are compressed and the signals are not affected, thus effectively improving the signal-to-noise ratio. However, the signal averaging method poses a compromise between signal-to-noise ratio and resolving power. Improving the sensitivity by simply increasing the ion gate pulse width introduces more ions into the drift tube to decrease the resolving power accordingly. The field-switching ion mobility spectrometer has high performance by injecting all ions formed in the near-zero field ionization region with strong pulse widths down to microseconds [35,36], thus narrowing the initial ion swarm introduced into the drift tube in a temporal-spatial compression manner. This greatly improves the resolving power and sensitivity [37].

An alternative method for data acquisition is to use multiplexing techniques that inject multiple ion packets into the drift tube in one data acquisition period. The ion mobility spectra are reconstructed by Fourier transform [38], Hadamard transform [27,39,40], matched filtering (cross-correlation) [41], and Fourier deconvolution [42,43] from multiplexed ion current and modulation sequences applied to the ion gate [44]. The Fourier deconvolution technique was applied to the multiplexing IMS experiment using linear chirp modulation, thus simultaneously improving the signal-to-noise ratio and resolving power. In contrast to the field-switching ion mobility spectrometer, the Fourier deconvolution ion mobility spectrometer improves the S/N by decreasing the noise level instead of increasing the signal intensity, thus improving the resolving power via the deconvolution theorem.

Here, we connected a Fourier deconvolution ion mobility spectrometer to a commercial gas chromatograph for the analysis of volatile and semi-volatile compounds. The ion mobility spectrometer uses an 63Ni source to produce a stable ionization efficiency and Fourier deconvolution to obtain the ion mobility spectra. The limits of detection, linear ranges, and resolving powers were evaluated and compared to those of the traditional signal-averaging method. We also used a complex real sample to explore the benefits and potential applications of this combination.