Degradation and Determination of the Residue of Metaldehyde in Tobacco and Soil

A method for determination of metaldehyde residues in tobacco was developed. Metaldehyde residues were extracted from tobacco with dichloromethane and cleaned up with the mixture column of aluminum oxide-activated carbon.Interfering aldehydes were removed with sodium meta-bisulphite solution.Metaldehyde was depolymerized with hydrochloric acid to acetaldehyde, which was reacted with 2,4-dinitrophenylhydrazine.The derivative acetaldehyde 2,4-dinitrophenylhydrazone was cleaned up on silica gel column and determined by GC-NPD.The limit of detection of metaldehyde was 0.04 ng.The limit of quantification of the method for pesticide in tobacco and soil was 0.02 to 0.10 mg/kg.The recoveries from 3 samples fortified with metaldehyde at levels of 0.02 to 1.0 mg/kg, ranged from 86% to 100%.And the RSD was below 15%(n=5).The study of the residue dynamics demonstrated that: 1) The absorption of metaldehyde was the highest 4 days after treatment, and then the absorption declined slowly.After 21 days, the residues of metaldehyde was 0.04 mg/kg nearing the limit of quantification.The half life of metaldehyde was 4 days in soil.2) When metaldehyde was used as the recommended dosage,the residues of metaldehyde was below 0.10 mg/kg in dry tobacco,thus no any contamination to tobacco product.