Sample Pretreatment And Chromatographic Analysis In Determination Of Fungicides Residues In Food

Food safety concerns everyone's health and has more attention around the world. With the expansion of industrial and agricultural production, pesticides, such as fungicides, insecticides and herbicides are more and more being actively manufactured and used in agriculture for crop protection. However, a great portion of the pesticides are carcinogenic, teratogenic and mutagenic to animals and human. In addition, some lipophilic pesticides are not biodegradable, thereby accumulate in soil, water surface, plants, bodies of animal, and are recycled via food chain, which in turn harms human located on the top of the chain. Hence, the development of analysis methods for the determination of pesticides residues in food is necessary to control food contamination and ensure food safety. There are two prominent problems in pesticides residues analysis, one is the pretreatment means, and the other is the separation and determination method. Since the food matrices are complex and pesticides residues are of trace level, furthermore, more rigid maximum residue limits (MRLs) have been established, more effective sample pretreatment and sensitive determination method should match the requirement of the rigid MRLs in pesticides residues analysis. Sample pretreatment is the most difficult process, but important step in pesticides residues analysis, which determines the sensitivity and feasibility of an analytical method. Development a cost-, labor- and efficiency-effective sample pretreatment method of pesticides residues analysis is key research task in this thesis.Now, a rapid, sensitive, high-efficient analytical method for determination of multiclass fungicides residues by gas chromatography is proposed and it meets the trend of modern analytical method for pesticide residues. Accurate quantification and identification of susceptive analyte can be seriously affected due to matrix induced enhancement or suppression effect that commonly encountered in the gas chromatographic analysis of pesticides in food. But there is little research on this at present. Some researches are performed and measures of counteract the matrix effect are proposed in this paper. Methods for eliminating pesticide residues from food matrix have also more attention by researcher, so a two-phase partition method was employed for the elimination of fungicides residues in ginseng extract.The details in the contents and results of the thesis are as follows:1. At first, matrix solid-phase dispersion and solid-phase microextraction for the determination of trace residues and contaminants in foods emerged in recent years were reviewed, and the most recent application in foods were summarized at the same time.2. A rapid method based on matrix solid-phase dispersion was developed for the determination of pentachloronitrobenzene (PCNB), pentachloraniline (PCA), methyl-pentachlorophenyl sulfide (MPCS), procymidone (PRO), captan (CAP) and Iprodione (IPR) in fruits and vegetables, wine and ginseng extract. After the optimisation of different parameters such as the type of adsorbent, the extraction solvent, and the extraction assistance by sonication. The analysis of samples was accomplished using gas chromatography with electron-capture detector (GC-ECD). Spiked blank samples were used as standards to counteract the matrix effect observed in the chromatographic determination. The recoveries of the method were in the range 82.6%—109.7%, 92.1%—101.5% and 90.2—108.3%, and good linear relationships (r~2＞0.999) with relative standard deviations lower than 15%. The limits of detections ranged from 0.1μg/Kg to 0.4μg/Kg. The proposed method were applied to the analysis of these compounds in fruits and vegetables, wine and ginseng extract samples.3. A headspace solid-phase microextraction (HS-SPME) with a 100μm PDMS fiber-coating combined with GC-ECD to determine 6 fungicides residues in aqueous solutions ginseng extract sample. The analytes in the study consisted of PCNB, PCA, MPCS, PRO, CAP and IPR. The following parameters were adjusted to optimize HS-SPME in order to obtain the maximum sensitivity: extraction temperature, extraction time, desorption temperature and time, effect of dilution on sample, the addition of salt. The limits of detection ranged from 1.5ng/Kg to 50ng/Kg for all fungicides. The recovery of the method was in the ranged from 86.7±11.2% to 113.2±10.6% and a good linear relationship (r~2=0.9964) with relative standard deviations not higher than 13.5%. The results demonstrate the suitability of the HS-SPME-GC-ECD approach for the analysis of multi-residue fungicides in ginseng extract.4. This study was carried out to develop a cost-, labor- and efficiency-effective elimination method of fungicides residues in ginseng extract. A two-phase partition method between soybean oil and aqueous ginseng extract was employed for the elimination of fungicides residues. Content of the fungicides was determined by GC-ECD. The range of distribution ratio of the fungicides to the oil layer was 80.9±5.1%—105.4±8.6% in the mixture of the oil and distilled water, and 85.7±9.8%—115.6±6.3% in the mixture of the oil and aqueous ginseng extract. No significant qualitative and quantitative change of ginsenosides, the active ingredients of Panax ginseng, was observed in the aqueous ginseng extract before and after the oil treatment. These results suggest that two-phase partition chromatography between soybean oil and the aqueous phase is a cost-, labor- and efficiency-effective reliable method for the elimination of fungicides residues in ginseng extract.