Extraction and isolation of triazine herbicides from water and vegetables by a double trap tandem system

The ability of a two-trap tandem system, one containing a nonspecific adsorbing material, such as graphitized carbon black (Carbopack B), and the other one filled with a sulfonic acid type silica-based cation exchanger (SCX), in extracting and isolating basic compounds from real matrices was evaluated by applying this device to the determination of triazine residues in water and vegetables. After percolation through the Carbopack column (extraction cartridge) of water samples or suitably prepared vegetable extracts, the two traps were connected in series, a methylene chloride-methanol mixture was allowed to flow along them, and triazines displaced from the extraction cartridge were selectively reabsorbed via salt formation on the strong acid exchanger column (isolation cartridge). After the column was washed, the analytes were removed from the isolation cartridge by 0.7 mL of aqueous methanol containing 70 mmol/L KCl. After the internal standard was added, the final solution was directly injected into the "high-performance" liquid chromatographic apparatus, which was operated isocratically in the reverse-phase mode with UV detection at 220 nm. The analytical recoveries of eight triazines from the two matrices considered ranged between 95% and 100%. The limits of sensitivity of this method for triazines were set at 10 ng/g of vegetable material and 10 ng/L of water by sampling 100 mL of it.