Solid-phase extraction preconcentration of 2,4-dichlorophenoxyacetic acid on silica with immobilized polyethoxylated isooctylphenol groups

Silica with immobilized polyethoxylated isooctylphenol groups (SiO (2) -TX) is studied as an adsorbent for the solid-phase extraction preconcentration of pesticides based on chlorophenoxyalkanecarboxylic acids from aqueous solutions. It is demonstrated that 2,4-dichlorophenoxyacetic acid (2,4-D) is efficiently (up to 96%) extracted as an ion associate with cetyltrimethylammonium bromide (CTMAB) with SiO2-TX in the pH range 8-10. The optimum CTMAB-to-2,4-D molar ratio is 200: 1. The capacity of SiO2-TX to 2,4-D in the Henry region is 0.42 mg/g of adsorbent, and the distribution coefficients reach 9 x 10(2) mL/g. It is shown that 2,4-D is quantitatively eluted with 1-2 mL of acetonitrile, which allowed us to use the adsorbent in a preconcentration cartridge before determining pesticides by HPLC. The procedure allowed pesticides to be recovered from aqueous solutions in concentrations beginning from 0.025 mg/L.