An optimized sol-gel technique was used for the entrapment of 2,4-dichlorophenoxyacetic acid (2,4-D) antibodies in a silica matrix derived from tetraethoxysilane (TEOS). Immunoextraction cartridges with reproducible binding capacity for 2,4-D methyl ester (test solute) were prepared from the doped dry gels and wet hydrogels. Although the surface of these biomaterials was characterized by wide macropores, there was no evidence of antibody leakage, as demonstrated by the good precision of the results obtained from repeated extractions performed in the same cartridge. The 2,4-D antibody (commercially obtained), free or encapsulated, was highly selective toward the esterified 2,4-D molecule. Optimal extraction was achieved from samples containing phosphate buffer 0.01-0.15 M (pH ∼7), which were loaded at a maximal flow rate of 1 mL min -1 in cartridges left under buffer for at least 30 min between consecutive experiments. Recoveries of 100%, for loaded ester amounts lower than the cartridge capacity, were obtained under these conditions. A binding capacity of 130 ng of 2,4-D ester per mg of immobilized antibody, corresponding to 42% of the free antibody activity, was obtained with the best gels. The capacity of these immunosorbent cartridges remained practically constant during eight weeks or 50-60 adsorption-desorption cycles.

Sol-gel immunosorbents (IS) prepared by encapsulation of polyclonal antibodies in silica were packed in cartridges and evaluated for selective immunoaffinity extraction (IAE) of malathion and triazines from aqueous samples. Encapsulated atrazine antibodies highly cross-reacted with simazine and propazine but did not recognize prometon and prometryn. No cross-reactivity of malathion antibodies was observed with the closely related metabolites oxomalathion and isomalathion. Mean IS binding capacities per milligram of entrapped antibody were 0.33 nmol of malathion and 0.47 nmol of atrazine (approximately 100 ng each). This capacity remained constant for at least 10 weeks, and the cartridge reusability was excellent (>60 IAE runs); also, high preconcentration factors were feasible because the breakthrough of analytes from IS cartridges did not occur up to the 250 mL sample volumes, provided that the capacity was not surpassed. Simple and rapid methods for determination of malathion or three triazines in surface water were developed using off-line IAE and HPLC-UV. The application to 50 mL dam water samples spiked at approximately 1 ng/mL of pesticides resulted in recoveries of approximately 90% and RSD < 5% (n=7). LODs for this sample volume (direct injection of IS eluates) were in the range of 0.15-0.50 ng/mL. Lower LODs (0.03-0.1 ng/mL) were achieved by online analysis of whole eluates previously loaded in RP precolumns.

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