DETERMINATION OF ATRAZINE AND HYDROXYATRAZINE RESIDUES IN SOIL BY ION-PAIR, REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

An improved method is presented for the determination of atrazine and hydroxyatrazine in soils. The method involves performing an initial extraction of the soil sample with a mixture (90:10 v/v) acetonitrile-aqueous 0.1 M hydrochloric acid. After centrifugation, the extract is concentrated onto a disposable strong cationic exchange, sulfonic acid-bonded, solid phase extraction (SPE) cartridge, and interfering soil substances are removed by rinsing. The atrazine and hydroxyatrazine are eluted with a 50:50 (v/v) acetonitrile-aqueous 0.1 M K2HP04 solution. The analysis was performed using a reversed-phase, high performance liquid chromatographic column of C18-bonded silica with an ion-pairing solvent system (50:50 v/v) acetonitrile-water containing 0.020 M n-heptanesulfonic acid and 0.10 M phosphoric acid. This isocratic solvent system provided an excellent separation of not only atrazine, simazine and propazine but also of hydroxyatrazine, hydroxysimazine and various dealkylated products of atrazine. An ultraviolet diode array detector provided linear calibration plots in the 0.1-10 ppm range, with lower limits of detection of 0.01 ppm for atrazine and propazine. This improved extraction and HPLC analysis method was used to monitor the persistence of atrazine in the soil of three local corn fields. Over the 130-day growing season of the corn, the levels of atrazine in the upper 2-3 cm of the soil were found to drop from 2.0 to about 0.2 ppm. No significant levels of hydroxyatrazine were found in the farm soils sampled.