Capillary liquid chromatography of chlorophenoxy acid herbicides and their esters in apple juice samples after preconcentration on a cation exchanger based on polydivinylbenzene-N-vinylpyrrolidone

A capillary liquid chromatography (cLC) method with gradient elution has been used to determine chlorophenoxy acid herbicides: 2,4-dichlorophenoxyacetic acid, 4-chloro-2-methylphenoxyacetic acid, 2-(2,4-dichlorophenoxy)propanoic acid, 2-(4-chloro-2-methylphenoxy)propanoic acid, 4-(2,4-dichlorophenoxy)butanoic acid, 4-(4-chloro-2-methylphenoxy)butanoic acid, 2-(2,4,5-trichlorophenoxy)propanoic acid, 2,4-dichlorophenoxyacetic-1-methyl ester and 2,4-dichlorophenoxyacetic-1-butyl ester in spiked apple juice samples with amounts between 0.025 and 0.150 mg kg−1 of each herbicide. Clean-up and preconcentration of acid and esters were carried out in an Oasis MCX polymer. Detection limits obtained by cLC, between 0.005 and 0.018 mg kg−1, allowed the determination of chlorophenoxy acids and their esters in apple juice samples around the levels permitted by the European Regulations, with recoveries in the range 84–99% and RSDs between 1 and 4%.