Development Of GC-FDIMS Technology And Its Application In The Determination Of Esters In Baijiu

Ion mobility spectrometry(IMS)is a gas phase ion separation technology,which has the advantages of fast analysis speed,high sensitivity,low cost,and plays an important role in the fields of homeland security,environmental analysis and food flavor analysis.Ion mobility spectrometry coupled with gas chromatography or liquid chromatography can provide two-dimensional orthogonal separation,which favors rapid analysis for complex samples.However,most commercially available gas chromatography-ion mobility spectrometer(GC-IMS)uses radioactive sources and signal averaging(SA)data acquisition methods.There are some drawbacks such as low ion utilization efficiency,narrow linear range,and limited signal to noise ratio.Also,there is a compromise between resolving power and sensitivity for signal averaing data acquisition method.Ion injection multiplexing and advanced signal processing technologies such as Fourier Transform Ion Mobility Spectrometry(FTIMS),Hadamard Transform Ion Mobility Spectrometry(HTIMS),and Correlation Ion Mobility Spectrometry(CIMS)have become proposed for many years to improve ion utilization and sensitivity.However,higher resolving power and sensitivity of multiplex ion mobility spectrometry still remain to be addressed.The main research results of this paper are as follows :Firstly,a corona discharge ion mobility spectrometer was designed built.The ion source and drift tube of the ion mobility spectrometer were designed by Solidworks software.Simulation of electric field and the trajectory of ions in drift tube was conducted by means of Simion software with finite element method.On the basis of electric field optimization,a stacked ring corona discharge ion mobility spectrometer was designed and assembled by using corona discharge ion source,stainless steel electrode,polyether ether ketone and polyimide film as insulation material.The instrument performance was evaluated by the reaction ion peak,the product ion peak of dimethyl methyl phosphate(DMMP)and 2,6-di-tert-butyl pyridine(DTBP),and the ion mobility spectrum was collected by the signal averaging method.The experimental results showed that the resolving power of the designed drift tube was up to 60,which was similar to commercially available instruments with similar instrumental configurations.Secondly,to address the problems of high noise and low resolving power of the custom-built corona discharge ion mobility spectrometer and the shortcomings of the existing multiplexing methods,the Fourier deconvolution super-resolution technology coupled with the linear frequency modulation method of ion gate was proposed for the first time to reconstruct the ion mobility spectra,and this new method is named as Fourier deconvolution ion mobility spectrometry(FDIMS).This approach modulates the ion gate with a linear square wave chirp sequence and synchronizes the data acquisition and ion gate modulation and then reconstructs the ion mobility spectra based on convolution theorems.The equivalent ion gate pulse width of the ion mobility spectrum can be reduced from 100～200 μs to 2.5 μs,which greatly improves the resolving power and simultaneously improves the signal-to-noise ratio of spectrum reconstruction.The effects of modulation frequency,modulation time,and sampling rate on resolving power and signal-to-noise ratio were investigated by using the reaction ion peak,DMMP and DTBP product ion peak,and the performance of FDIMS was compared with FTIMS and CIMS.Compared with SAIMS,the Fourier deconvolution method can improve the signal-to-noise ratio by about 13 times and increase the resolving power significantly.Compared with FTIMS,FDIMS significantly improves resolving power and SNR.Compared with CIMS,the spectrum of FDIMS provides higher SNR,and the resolving power is also improved.More importantly,the acquisition time of the Fourier deconvolution method can decreased to hundreds of microseconds,which is crucial for the combination with pre-separation technology such as gas chromatography.Finally,the custom built corona discharge ion mobility spectrometer was coupled with gas chromatography(GC),and the performance differences of Fourier deconvolution and signal averaging methods applied in GC-IMS were studied.The detection limits and quantitative ranges of ethyl acetate,ethyl lactate,ethyl butyrate,isoamyl acetate,isobutyl acetate compounds in Baijiu were determined by GC-SAIMS and GC-FDIMS.The five ester contents in Baijiu with different flavor types were analyzed by the established instrument and the developed method.The experimental results showed that the five esters had a good linear relationship on the GC-IMS.The detection ability of GC-FDIMS was about three times that of GC-SAIMS,with RSD<6.99 %,with satisfied instrument reproducibility.