Evaluation of double solid-phase extraction system for determining triazine herbicides in milk

High-performance liquid chromatography with UV detection was used to determine eight triazine herbicides in milk. Solid-phase extraction was performed using a double trap; first, a nonspecific adsorbent (Carbograph), and then a cation exchanger (SCX). Eluate from the SCX was evaporated to dryness under reduced pressure and redissolved in mobile phase. An aliquot was injected into the chromatograph, which was operated isocratically in the reverse-phase mode with UV detection at 225 nm. Analytical recoveries for the eight triazines ranged from 73.0% to 92.4%. The limit of sensitivity of this method was about 0.09 ng mL-1of milk. The method was validated and evaluated by comparison with a method reported in literature.