Study On The Analysis Methods And The Influence Factors For Fumigants Residues

With increasing attention on food safety issues, the problem of fumigants residues in raw cereals has roused extensive concern. By now, there are some methods for determining fumigants residues in agricultural crops. However most of them usually require large amounts of solvent and time-consuming. In this way, it is necessary to develop a fast and sensitive method to analyze the residues in raw cereals. In this essay, with the aim to develop sample preparation methods for analyzing raw cereals samples, several pretreatment procedures, such as ultrasonication assisted extraction (UAE), accelerated solvent extraction (ASE) and the solid phase microextraction(SPME) were studied, which was proved to be practical and reliable for the residues analysis with HS-GC-ECD. The thesis mainly includes the following four parts.1. The method for determination of bromomethane residues in raw cereals by static headspace gas chromatography was established. The whole sampling process, using water as extraction solvent, only including an ultrasonic assisted extraction step and a static headspace step, can be completed within 30min. Limits of detection was less than 0.016 mg/kg. Recoveries of spiked samples were 94.79%-107.03%, with relative standard deviations (RSD) of 4.3%-8.3%. The results indicated that this method was easy in operation with acceptable sensitivity, recovery and reproducibility.2. Accelerated solvent extraction (ASE) and ultrasonic assisted extraction were compared for their effectiveness in the extraction of fumigants residues from raw cereals. The ASE parameters (temperature, extraction time, number of cycles and solvent composition) were optimized in order to maximize the amount of fumigants extracted. Then the HS-GC-ECD was applied to the quantitative analysis after extractions. Effects of different gas-liquid phase ratio, equilibrium temperature, equilibrium time and salt on sensitivity of real sample were discussed. Limits of detection were less than 0.001 mg/kg for Chloropicrin and 0.003mg/kg for 1, 2-Dibromoethane (EDB) respectively. Recoveries of spiked samples by ASE were 91.5%-106.3%, with relative standard deviations (RSD) of 4.6%-9.4%. The ASE method showed better recoveries than UAE method under the low concentration. The results indicated that this method was easy in operation with acceptable sensitivity, recovery and reproducibility.3. The extraction procedure of fumigants residues from raw cereals using water as extraction solvent with the aid of ultrasonic followed by the solid phase microextraction (SPME) was established. The whole sampling process,only including an ultrasonic assisted extraction step and a solid phase microextraction step,can be completed within 30min.Limits of detection were less than 0.005 mg/kg for Chloropicrin and 0.009mg/kg for EDB respectively. Recoveries of spiked samples were 87.5%-108.4%, with relative standard deviations (RSD) of 11.2%-18.3%. The results indicated that this method was a suitable and fast method for screening of fumigants residues directly in raw cereals. 4. The determination method of fumigants residues was used to detect samples in the process of simulated fumigations. In order to analyze the influence factors of fumigants residues, the time, temperature and humidity conditions were studied. The results indicated that the influence of temperature and humidity was obvious, and the substantial time of airiness was an effective way to reduce the amounts of fumigants residues.