Study Of In Situ/in Vivo Solid-Phase Microextraction-Gas Chromatography Method For Organophosphorus Pesticides In Citrus

Solid phase microextraction(SPME)is a technique that combines extraction,separation,concentration and injection into a single step.The fiber and its device is mini-sized and portable,which causes slight invasiveness to living systems.Therefore,the application of SPME in in situ and in vivo sampling has become a new trend in recent years.In vivo/in situ SPME sampling technology causes less invasive damage to the living system and can be conducted in the natural state of animals and plants.In vivo/in situ SPME sampling can be performed in the same experimental object repeatedly to trace the analytes in real-time uptaking and elimination,which greatly reduces the consumption of samples and avoids the experimental errors caused by individual differences.The sampling requires no sample pretreatment,and is simple and fast.Meanwhile,it can also capture some important information about the unstablecompounds and reflect the real condition of the target analytes in biosystem.In this research,a sol-gel polydimethylsiloxane(PDMS)fiber was prepared for the determination of organophosphorus pesticides(OPPs)in citrus.Methods of direct-immersion SPME/gas chromatography(DI-SPME/GC),in situ-SPME/GC and in vivo-SPME/GCwere established for analysis of OPPs in citrus.The main results were as following:1.The study of DI-SPME/GC method for determination of OPPs in citrus pulpA DI-SPME/GC method was established for analysis of five OPPs in citrus pulp with a sol-gel PDMS fiber.The fiber exhibited superior extraction capability to commercial PDMS,PA and PDMS/DVB fibers.The five OPPs in the citrus matrix were stable within 32 h at 4℃(P>0.05).The citrus pulp was diluted by equal amount of water,adjusted to p H 1.84,and subjected to DI-SPME at 50℃for 60 min with a stirring rate of 1 200 r/min,and good linear ranges were obtained with linear regression coefficients(R~2)greater than 0.999 for all test compounds in citrus matrix.The limits of detection ranged from 0.002 to 0.046μg/kg.Good repeatability(0.5%～15.6%)and high recoveries(71.0%～125.3%)were achieved.The method was very sensitive,precise and accurate and the sample pretreatment was very simple and rapid.The sol-gel coating exhibited good extraction reproducibility and avoided fouling in the complex citrus matrix,which shows that it has good matrix-compatibility.2.The study of in situ SPME/GC method for the determination of OPPs in citrusA sensitive and rapid in situ SPME sampling method for the determination of five OPPs in citrus was first established by sampling rate calibration method.The sampling rates determined in homogenized citrus by DI-SPME were different from those obtained by in situ SPME sampling,revealing that the sampling rates determined in spiked homogenized citrus by DI-SPME could not be used to quantify the concentrations of the analytes in in situ SPME for spiked citrus.Low limits of detection(ranging from 0.33 to 4.05μg/kg)were achieved with a sampling time of 25min,which were much below the MRLs established by China Food and Drug Administration(GB 2763-2016)and the European Union.The concentrations determined by in situ SPME/GC-NPD and DI-SPME/GC-NPD were quite similar(P>0.05),demonstrating the accuracy of the present method.Finally,the real-time uptaking and elimination processes of pesticides in spiked citrus in 1 466 min were traced.3.The study of in vivo SPME/GC method for the determination of OPPs in citrusA sensitive and rapid in vivo SPME/GC method for the determination of fenitrothion in citrus was first established with a sol-gel PDMS fiber by sampling rate calibration method.The fiber exhibited good reproducibility in in vivo sampling and could be used at least 50 times in citrus,which presents good application prospect of sol-gel coating in in vivo SPME in future.The sampling rate of fenitrothion in citrus was 185.95μg/min.A limit of detection of 8.26μg/kg was achieved with a sampling time of 25 min,which was much below the MRLs established by China Food and Drug Administration(GB 2763-2016).The concentrations determined by in vivo SPME sampling method and DI-SPME/GC-NPD were quite similar(P>0.05),demonstrating the accuracy of the present method.The distribution of OPPs inside a citrus fruit and among citrus fruits were extremely uneven(P<0.05),which showed the necessity of in vivo/in situ sampling.Finally,the real-time uptaking and elimination processes of fenitrothion in citrus by in vivo SPME sampling method during 11 days were traced.This method is simple and rapid,cause less damage to the citrus and can be used to sample the same experimental object repeatedly.