We characterized in vitro adsorption of representative chemicals in candidate gel/charcoal matrices being investigated for use in noninvasive transdermal chemical collection. Binding properties of three model compounds of widely varying water and lipid solubilities (theophylline, methotrexate, and parathion) were studied in hydrophilic (agarose, or polyvinyl alcohol/polyvinyl pyrrolidone) and lipophilic (silicone) gel/charcoal compositions. Analysis of adsorption isotherms indicate that agarose is the superior gel selection for hydrophilic compounds such as theophylline and methotrexate (greater than 90% uptake for each), and that a silicone lipogel allows for greatest lipophilic (parathion) adsorption (greater than 95% uptake).