Research And Application Of Ion Mobility Spectrometry In Analysis Of Food Safety

Ion mobility spectrometer （IMS） has been developed as an instrumentalanalytical technique for detecting and identifying organic compounds basedupon the characteristic mobility coefficients of gas phase ions in a weakelectric field which depend on the molecular weight, charge and shape of theions. The apparatus is fast, sensitive, robust and easy to miniaturize for fieldoperation, thereby providing an inexpensive and efficient tool for the analysisof various trace amounts of chemical compounds. In this paper, IMStechnology was used to detect pesticide residues in fruit and vegetablematerial.1. An instrumental analytical approach was developed for rapid detectionof malathion and dichlorovos using a hand-held ion mobility spectrometer（IMS）. During the tests, the IMS was operated in the negative mode at ambientpressure using⁶³Ni as the ionization source and dry, clean air as drift gas whichcirculated in a closed loop system. Tests were first conducted to optimize theoperating parameters including the inlet temperature, drift tube temperature,drift gas flow rate and carrier gas flow rate. Under the optimized operating conditions （inlet temperature of180℃，drift tube temperature of150℃，carrier gas flow rate of0.6L/min and drift gas flow rate of0.6L/min）, thedetection limits for dichlorovos and malathion were1ng and5ng respectivelywith the analysis time of less than10s. Simulated actual samples with pesticideresidues were prepared by adding dichlorovos and malathion to the skin ofcherry tomatoes. Pre of the sample was adopted by extracting the pesticideresidues from the cherry tomatoes distilled acetone to obtain the sample usedfor detection under the same operating conditions. The results indicated thatthe approach is simple, rapid and acceptably reproducible with the relativestandard deviation values of8.31%and7.17%for dichlorovos and malathionrespectively, thereby showing great potential as a method for rapid screeningand detection of dichlorovos and malathion residues contained in agriculturalproducts.2. A liquid-phase microextraction （LPME） methodology based on the useof porous polyvinylidene fluoride （PVDF） hollow fibres was developed forextracting seven pesticides from cucumbers. The seven pesticides includepropoxur, carbofuran, atrazine, cyanatryn, metolachlor, prometryn andtebuconazole. The PVDF hollow fibre provides higher extraction efficiencydue to its higher porosity and better solvent compatibility. A new desorptionmethodology was developed since some pesticides were absorbed by the wallpore of the PVDF. Ultra-high pressure liquid chromatography coupled totandem mass spectrometry （UHPLC-MS/MS） was used for pesticide analysis. In order to obtain high recoveries and enrichment factors of the analytes,several parameters such as method of sealing, acceptor phase （organicsolvents）, stirring speed, extraction time, salting out effect, desorption modeand time were optimized. A fast, simple method for closing fibre ends waspracticed by using mechanical crimping. Pesticides were extracted from thesample to the organic solvent and then desorbed in mixture methanol:water（1:1v/v） prior to chromatographic analysis. Limits of detection （LOD） for themulti-reaction-monitoring （MRM） mode of the method varies from0.01to0.31μg/kg with optimized sample preparation. Calibration curves are linearwith R²≥0.99. Enrichment factor of the hollow fibre LPME ranges from100to147. Matrix effect has been considered and is in the range of76to122%.The relative recoveries from cucumber samples are between63%and119%with the relative standard deviation （RSD, n=6） lower than20%.3. This paper develops an instrumental analytical approach for the rapid,fast detection of seven pesticides using a hand-held ion mobility spectrometer（IMS）. The hollow fibre liquid phase micro-extraction （LPME） samplepreparation method was used to preconcentrate the pesticide residues present incucumber samples. The sample preparation method was validated by ultra-highpressure liquid chromatography coupled to tandem mass spectrometry（UPLC-MS/MS）. The extracted pesticide residues were then detected by IMSunder the optimized operating conditions （inlet temperature of195℃，drift tubetemperature of180℃，carrier gas flow rate of0.6L/min and drift gas flow rate of0.6L/min）. During the tests, the instrument was operated in the positivemode at ambient pressure using⁶³Ni as the ionization source, with dry, cleanair as drift gas which circulated in a closed loop system. The IMS detectionlimits for propoxur, carbofuran, atrazine, cyanatryn, metolachlor, prometrynand tebuconazole were5,5,1,5,5,10and50ng respectively. The analysis viaIMS takes less than10s, compared with6mins via UPLC-MS/MS. Matrixeffect has different influence on seven pesticides. The method can meet therequirment of maximum residue limits. The results indicate that the approach issimple, rapid, and acceptably reproducible, thereby showing great potential asa method for rapid screening and detection of seven pesticides residuescontained in agricultural products.