| Ion mobility spectrometry (IMS) is a trace analytical method for characterizing ions that are formed from molecules in a sample based on their mobility. Unlike mass spectrometry, IMS can work in atmospheric environments without the need for a vacuum system. It also has the advantages of rapid response, low detection limit, simplicity, and portability. Currently, IMS-equipped, handheld analyzers are widely used to detect gaseous or solid analytes. In this paper, a new rapid detection method for liquid analytes based on IMS was presented to meet the demand for in-situ rapid detect trace liquid analytes in the field of homeland security, medical and biological. An implementation for a paper spray ionization ion mobility spectrometer (PSI-IMS) was reported after focusing on several key technical issues.The main works are summarized as follows:First, a numerical simulation method was developed based on finite-element analysis to optimize the structure of the drift tube and to improve the resolving power of IMS. Firstly, a numerical simulation of the electric field in the traditional drift tube was conducted. The influences of some important factors such as thickness of electrode and insulating ring, inner diameter of drift tube as well as the metal enclosure of the drift tube on the homogeneity of electric field were researched. On the basis of the research, some empirical laws were concluded, which can help designers to improve the performance of ion mobility spectrometry. Then, a flow field model was presented. Based on the simulation results, an improved gas structure was explored. Simulation results show that the improved gas structure effectively extends the drift tube airflow uniformity region. Finally, a multiphysics coupling model was provided based on particle tracing module of COMSOL Multiphysics, which provides a Lagrangian description of a problem by solving ordinary differential equations using Newton’s law of motion. Compared with the traditional buliding testing prototype method, the simulation results can help shorten the instrument development cycles and save development costs.Second, other key techniques except the drift region of the PSI-IMS were studied. Firstly，several key issues about combination paper spray ionization source with ion mobility spectrometer were researched, such as the type and shape of selected paper for ionization, the interface design issues, the voltage selection between the paper and the counter electrode. Then, a physical ion restraint mechanism and a proper gas inlet method for remove solvent were presented for the reaction zone, which can improve the instrumental signal response without increasing the complexity of the instrument. Besides, an easy, simple, and reliable Bradbury-Nielsen gate for ion control in the home-built ion mobility spectrometry was designed and investigated. The gate was made with printed circuit board (PCB) technology. The performance of the gate was validated by testing water and acetonitrile solvents based on the home-built paper spray ionization ion mobility spectrometer. Finally, the data processing algorithm applied in the home-built ion mobility spectrometer was studied, including digital filtering algorithm and spectral peak detection based on differential method.Later, an implementation for a PSI-IMS was provided based on above key technologies. The performance of the home-built paper spray ionization ion mobility spectrometer was tested by measuring a standard analyte,2,6-di-tert-butyl pyridine (2,6-DtBP), and the results were in good agreement with those previously reported by ESI-IMS. The measured resolving power for2,6-DtBP was dependent on the drift gas flow, gate pulse width, and temperature. The resolving power was improved with a moderate drift gas flow, reduced gate pulse width, and lower temperature. The highest resolving power (47) was measured for2,6-DtBP. Based on these preliminary results, the present PSIMS design is anticipated to be a useful tool of choice for rapid analysis of liquid samples. Handheld or portable IMS devices coupled with a paper spray ionization source are expected to become a tool for field and real-time measurements of liquid samples.Finally, a new method for the rapid detection of liquid-or solid-phase cocaine without any sample pretreatment based on paper spray ionization ion mobility spectrometry was studied. The method can potentially achieve on-site detection of both liquid-phase and solid-phase samples. For rapid analysis of liquid-phase cocaine, a limit of detection (LOD) was found to be2mg/L (S/N=3) and the entire time including sample introduction and analysis is less than1min. Good linearity was obtained within the concentration range of two orders of magnitude, with a correlation coefficient of99.2%and a relative standard deviation (RSD) of6.5%(for50mg/L, n=11). For rapid analysis of solid phase cocaine, a LOD was found to be5mg/L(S/N=3). The linear range was from10to200mg/L with a correlation coefficient of99.7%and RSD of6.3%(for100ng, n=11).We also have demonstrated the capability of the PSI-IMS method for direct detection of cocaine in real samples. Cocaine residues on variety surfaces can be analyze directly after wiping the samples to a paper triangles. Based on the preliminary results, the PSI-IMS method has great potential to be applied in on-site detection of trace illicit drugs and to help social scientists and authorities to combat drug abuse. |
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