A mathematical model is developed and implemented to characterize the pickup of various liquid chemical contaminants by polyethylene-coated magnetic particles. The model and its associated experimental and analytical protocols were applied to a wide range of liquid chemicals in order to gain insights into the physical basis for the pickup phenomenon. The characteristics of the pickup isotherms range between "ideal" and "nonideal" behaviors that are reflected in the mathematical model by a single parameter, alpha(0), where alpha(0) = 1 corresponds to ideal behavior and alpha(0)>1 corresponds to a departure from idealized behavior that is directly quantified by the magnitude of alpha(0). The parameter alpha(0) is also related to the efficiency of pickup, and since most isotherms observed in the study deviate from ideality, the high efficiency of pickup observed in these systems has been attributed in part to this deviation. The proposed model and its associated experimental and analytical protocols demonstrate great potential for the systematic evaluation of the uptake of chemical contaminants using magnetic particle technology.