A Study Of Analytical Methods For Azoxystrobin Residue In Fruits And Vegetables By Gas Chromatography

Azoxystrobin is one of strobilurin fungicides, which are synthetic analogue of naturally occurring fungal metabolites. Pesticides that contain azoxystrobin are recommended for protection of fruits and vegetables against powdery and downy mildew and grey mould. It can be also used to protect cereals against fungal diseases such as powdery mildew, stem rust, leaf rust, and black stem rust, and to protect fruits against blet and mildew. The fungicides thus have a wide range of applications and are commonly used in agriculture. It is, therefore, necessary to determine levels of azoxystrobin residues in plant material.A rapid and sensitive method using gas chromatography with nitrogen -phosphorus detection (GC/NPD) has been developed for the determination of azoxystrobin in apple, orange, grape, cabbage, tomato, potato and cauliflower. Azoxystrobin was extracted from these fruits and vegetables with 50:50/ethyl acetate: cyclohexane, the distill solution was dehydrated by anhydrous sodium sulfate and the aliquot was evaporated to near dryness under a gentle stream of nitrogen. The residuum was dissolved in cyclohexane and filtered through a 0.45μm filter for gas chromatography analysis.Sample of 5μl was automatically injected into the GC/NPD. All the chromatographic analyses were performed on an Angilent-6890 GC, equipped with nitrogen -phosphorus detection (GC/NPD). The capillary column was HP-5 (30m×320μm×0.25μm). The splitless injector temperature was operated at 300℃, The oven temperature programmed from an initial 180℃to 280℃at a rate of 30℃/min and held for 8min, and 280℃to 300℃at a rate of 30℃/min held for 5min at the final temperature. Nitrogen at the flow rate of 1.8ml/min was used as carrier gas. The temperature of the nitrogen -phosphorus detection was 300℃. Rubindium voltage was 3.35V. Hydrogen was at a flow-rate of 4ml/min, and it was closed in 0~2.0min. The retention of azoxystrobin is 6.737min. The time required for chromatographic analysis was 15 min.The operating ranges of the chromatographic analysis were determined. The LOD of the standard solution were 0.005mg/L. Calibration graphs were good linearity over the concentration ranges tested (0.05~5mg/L, R=0.99966). LOD of 0.005mg/L were obtained for the analysis of azosystrobin in apple, orange, grape, cabbage, tomato, potato and cauliflower. The infra-day and inter-day precisions and the results for accuracy fell with the ranges specified.Lastly, the established detecting method is evaluated; it is measured by the lowest detecting concentration, the rate of accession reclaim and differentiation coefficient. The lowest detecting concentration reaches to 0.005mg/kg; the respective rate of accession reclaim of the azoxystrobin is 71.4%~109.2%. The three indexes are all go along with requests. Our experiment used gas chromatography with nitrogen–phosphorus detection, but residue determination can also be confirmed by use of electron capture detection in some degree.