Simultaneous determination of 13 phenoxy acid herbicide residues in soybean by GC-ECD

In this study, a gas chromatography method for the multiresidue determination of 13 phenoxy acid herbicide residues (4-CPA, 4-CPP, phenoxy butyric acid, dicamba, MCPA, MCPP, MCPB, 2,4-D, 3,4-D, 2,4,5-T, 2,4,5-TP, 2,4-DP, and 2,4-DB) in soybean was developed. After the removal of fat using n-hexane, the sample was extracted with acetonitrile-50 mM HCl (v/v 7:3), and then followed by liquid-liquid partition with n-hexane (saturated by acetonitrile). The soybean extract was further cleaned up by anion exchange column. Then the residues were derived with pentafluorobenzyl bromide and the resulting pentafluorobenzyl (PFB) esters were analyzed by a gas chromatograph equipped with an electron capture detector (ECD), quantified by the external standard method. Recoveries of spiked samples at two fortified levels (0.01 and 0.1 mg/kg) are all above 70%. And the relative standard deviation was less than 20%. It shows that the limits of determination (LOD) of this method (S/N >= 3) can meet the requirement of maximum residue analysis in import/export inspection for soybean.