Preconcentration of phenoxy acid herbicide residues by using an ion exchanger based on MFE-Polymer

An anion exchanger based on MFE-Polymer (hydroxyethylmethacrylate, HEMA) containing quaternary ammonium functional groups has been used to pack a 150 x 4.6 mm id steel column, and the efficiency of this ion exchanger to preconcentrate phenoxy acid herbicides residues has been studied. The phenoxy acid herbicides studied were 2,4-dichlorophenoxy acetic acid (2,4-D), 4-(2,4-dichlorophenoxy)-butanoic acid (2,4-DB), 2,4,5-trichlorophenoxy acetic acid (2,4,5-T), 2-(2,4,5-trichlorophenoxy)-propanoic acid (2,4,5-TP), and 4-chloro-2-methylphenoxy acetic acid (MCPA). Dicamba (3,6-dichloro-2-methoxybenzoic acid), a benzoic acid herbicide usually used in technical products in mixtures with some of the related phenoxy acids, has also been included in the study. Retention of these herbicides on the referred ion exchanger is possible in aqueous acidic medium, probably because of the high polarizing power of the quaternary ammonium groups over the studied herbicides. Subsequent elution from the column was made with methanol containing nitric acid 60 mM and not more than 10 mL are required. The influence of the flow rate in the retention of the herbicides was evaluated in the 1.0 - 9.0 mL/min range, achieving recoveries around 100% for all of the herbicides studied. Regarding the capacity of the anion exchanger, the column prepared can retain up to 1000 mu g of each herbicide. The good ability for retention and elution allows the LC determination of these herbicides in tomato samples at levels of 0.05 mg/kg with a minimum clean-up.