Studies On The Matrix Effects In The Pesticide Residue Analysis Of Tea

To better understand the matrix effects in pesticide multi-residue analysis in tea, matrixeffects of tea with different origin and type were studied, and methods using the combinationof analyte protectants to overcome matrix effects in GC-MS and GC-MS/MS analysis ofpesticide residues in tea matrix were proposed.In this thesis,28varietals of tea which are the products of national geography symbolwere selected to be studied for the matrix effects in GC-MS and GC-MS/MS analysis.Chemometric methods were used to classify the teas. Tea samples were divided into threeclusters: the first cluster consisted of not fermented and slightly fermented tea samples; thesecond cluster were composed of semi-fermented tea samples; the third cluster consisted offully fermented and post-fermented teas. Any type of tea can be chosen from each cluster ascorresponding representative matrix within this cluster to make matrix-matched solutions. Theresult provides a good theory basis for the selection of representative matrix for tea. Therepresentative tea matrix could simplify the operation of the experiment while guarantee theaccuracy of the experiment.Different APs were evaluated to find the most suitable ones for improvingchromatographic quality of the signal. The influence of the APs on the peak shape andabundance were studied. The concentration and combination of different APs were alsoevaluated. A method to compensate for the matrix effects in the determination of186pesticideresidues in tea by GC-MS using analyte protectant was proposed. A mixture of triglycerol andD-ribonic acid-γ-lactone (both at2mg/mL in the injected samples) was found to be the mosteffective in improving the chromatographic behavior of186pesticides. The proposed methodwas quick and convenient, with good sensitivity and precision and the limit of quantificationcould reach the residue analysis requirements. The influence of the APs combination on thestability of the instrument was also investigated. The combination of APs resulted inruggedness improvment and consequently, reduced the maintenance for GC. As compared tomatrix-matched standardization, the analyte protectant approach offers a more convenientsolution to the problems associated with calibration in routine analysis of pesticide residuesand reducing need for frequent maintenance. A GC-MS/MS analytical method was developed for simultaneously determining205pesticides in tea matrices using analyte protectants to counteract the matrix-induced effect bythe same evaluation method of GC-MS. A mixture of triglycerol and D-ribonic acid-γ-lactone(both at2mg/mL in the injected samples) was found to be the most effective APs. Thelinearity, sensitivity, accuracy and precision of the method were validated. The combination ofAPs improved the ruggedness of GC-MS/MS. The category and concentration of the APs inthe proposed methods of GC-MS and GC-MS/MS were the same which means that thedifference of the detector is not the main influence of the matrix effect. The matrix effects oftea are mainly caused by the gas chromatography system.