To achieve irreversible (covalent) capture of monochlorotriazine herbicides such as atrazine, three commercially available poly(styrene) resins (Janda Jels) that vary in size were modified with reactive isonipecotic acid groups. The materials were characterized using the Kaiser test, infrared (IR) spectroscopy, and titration experiments that indicated the relative number of accessible nucleophiles. Sequestration of atrazine from aqueous solutions using these polymers was monitored using liquid chromatography-mass spectrometry. Large (50-100 mesh) and medium (100-200 mesh) resins remove all detectable traces of atrazine from water at similar rates, whereas the smallest resin (200-400 mesh) removes the herbicide at a slower rate. Generally, the sequestration of atrazine by reactive, nucleophilic resins seems to be a suitable strategy for additional inquiry, particularly as an alternative to the current method of wastewater treatment-activated charcoal.