Determination of Glyphosate Residues in Soil and Apple by Capillary Gas Chromatography with Nitrogen-Phosphorus Detection

A simple,sensitive and selective method using gas chromatorgaphy(GC)was developed to determine residues of glyphosate in soil and apple.The soil sample was extracted with 2 mol/L NH4OH,treated with trifluoroacetic anhydride(TFAA) and trifluoroethanol(TFE),and then determined by gas chromatorgaphy(GC)with nitrogen-phosphorus detector (NPD).The limit of detection was estimated to be 9×10-12 g,and the minimum determination concentration of glyphosate in soil samples was 0.02 mg/kg.The ranges of average recoveries and coefficient variation of the method were 84.4%~94.0% and 7.46%~10.40%,respectively.Apple samples were extracted with deionized water and cleaned by extraction with dichloromethane and solid phase extraction with BIO- RAD AG 50W-X8 cation exchange columns,then TFAA and TFE,and detected by GC-NPD.The limit of detection and the minimum determination concentration of glyphosate in apple were the same as the soil samples,but the ranges of average recoveries and coefficient variation of the method were 80.7% ~98.6% and 9.3% ~11.8%,respectively.The structure of derivative compound was confirmed by gas chromatography-mass spectrometry(GC-MS).Dissipation study showed that the half-life obtained for glyphosate in soil was approximately 9.2 days at 1.5 times of the recommended dosage in an apple orchard.No glyphosate residues was detected in apple and soil samples at treatments of 1 350 ~2 025 g(a.i.)/hm2 at harvest season (75 days after the treatment).