Determination of acid and hydroxybenzonitrile herbicide residues in soil by gas-liquid chromatography after ion-pair alkylation
The herbicides are extracted from soil with saturated calcium hydroxide solution. After clean-up the residues are ethylated using iodoethane and tetrabutylammonium hydrogen sulphate as counter ion. Liquid-liquid partition and the use of a macroreticular resin column were compared as clean-up steps and the reaction conditions for optimum yield of ethyl ester or ether were evaluated. Recoveries in excess of 80% were achieved for 2,4-D, dicamba, 3,6-dichloropicolinic acid, dichlorprop, picloram, 2,4,5-T, fenoprop, 2,3,6-TBA, bromoxynil and ioxynil.