The HPLC–microfiltration method previously described for determining atrazine and hydroxyatrazine species in organic soil has been adapted to a mineral soil. The method was able to monitor atrazine concentrations of less than 1.0 × 10−6 M, which is over 40 times lower than the atrazine concentrations measured in the earlier organic soil experiments. During kinetics.experiments, it also monitored four free and sorbed chemical species instead of only one. Measurements were obtained with much better accuracy and productivity than can be obtained by conventional methods. The atrazine sorption capacity of the mineral soil was also measured. The analytical chemical data produced can support heterogeneous chemical kinetics calculations.