| High-field asymmetric waveform ion mobility spectrometry(FAIMS)is a trace level analyticl technique for separation,detection and characterization of ions in gas-phase based on the difference in nonlinear variation of ion mobility with high electric field changed.Besides speed and sensitivity advantages of classical IMS,FAIMS has unique characteristics of miniaturized analyzer,on-site detection and isomers separation.Independently or tandemed with gas chromatography or mass spectrometry,FAIMS has been applied in qualitative fields such as explosives detection,drug detection,etc.However,due to the lack of wide-range quantitative model,there are very few applications in quantitative fields such as food safety analysis and environmental quality analysis.The main bottlenecks are:1)Research in ion-transmission process is neglected:Ion separation and substance detection process is composed with ionization,ion transmission,ion separation and ion detection in FAIMS.However,all theory and simulation have neglected the ion loss in ion-transmission process and focused on that in separation process up to present.These studies assumed that the ion concentration at the inlet of the separation region was uniformly constant.It implied the assumption that there was no ion loss from ionization region to separation region,which was contrary to the plasma recombination theory at atmospheric pressure.2)Over-limited experiments:The ion motions are extremely complicated,and there are many physical and chemical effects(ion recombination,diffusion,oscillation,ion drift included)under the influence of coupling field in microspace.The over-limited experimental range can't underline the effects of various parameters.Thus,the significant effects of key parameters can't be highlighted,and further led to the validity of conclusions can't be verified.In addition,the ionization source based on Atmospheric Pressure Chemical Ionization(APCI)has complex chemical processes and is another important problem for quantitative difficulties.Faced with the above bottlenecks,the ion loss in FAIMS and the quantitative ananlysis of Volatile Organic Compounds(VOCs)was investigated systematically by incorporating plasma recombination theory under atmospheric pressure with VOCs as analytes and vacuum ultraviolet(UV)light as ionization.The research contents and innovations as following:1)To solve the first bottleneck,the mathematical model of ion-recombination loss and its influencing factors was investigated by incorporating plasma recombination theory under atmospheric pressure,The recombination-loss factor was introduced for the first time in this theory,which described the influence of carrier gas flow rate,sample concentration and analyzer size on the ion-loss during transmission process.2)To solve the second bottleneck,the influence of ion diffusion effect and ion neutralization effect on ion loss in separation process were analyzed,and a multi-parameter,wide-range quantitative model of FAIMS was proposed based on the above theory and ion-separation loss model proposed by Krylov.3)A highly integrated,high resolution,high sensitivity FAIMS prototype and software platform was established,and the above mathematical models were verified one by one based on this experimental platform.Quantitative detection of VOCs in wide separation voltage range?wide flow range and wide concentration range was achieved.The experimental results verified the correctness of the wide-range quantitative model proposed in this study.4)To realize the simultaneous qualitative and quantitative analysis of the volatile organic mixture and enhance the application of FAIMS from qualitative fields to quantitative fields.A simultaneous separation and detection method that "fingerprint feature acquisition-separation parameter selection-isomers experimental analysis" was proposed.The simultaneous separation and detection of xylene isomers was achieved,and the experimental results revealed the superposition feature of FAIMS spectrometry.On this basis,the quantitative relationship of the xylene isomer mixture was given,and the relative errors of simultaneous quantitative detection of o-,m-,and p-xylene misture were only 1%,0.1%,and 3%.This study provides an important method for FAIMS to realize the simultaneous separation and detection of VOCs mixture,and it provides a quantitative model of FAIMS applied in on-site detection of VOCs.More importantly,it is an important part of the work enhancing FAIMS from qualitative fields to broader fields of quantitative analysis. |
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