Rapid estimation of readily leachable triazine residues in soils using automatic kinetic bioaccessibility assays followed by on-line sorptive clean-up as a front-end to liquid chromatography

An automatic batchwise bioaccessibility test was proposed for on-line monitoring of readily mobile pools of ametryn and atrazine residues in agricultural soils with different physicochemical properties. A 0.01 mol L-1 CaCl2 solution mimicking rainwater percolation through the soil profiles was used for the herbicide extractions. The extract aliquots were successively sampled at regular time intervals in order to investigate the extraction kinetics. For extract clean-up and retention of freely dissolved target species, 30 mg of restricted-access like copolymer were used as in-line sorptive material followed by elution with methanol and on-line heart-cut injection towards a C-18 silica reversed-phase monolithic column (100 x 4.6 mm) in a liquid chromatographic system. A mathematical model emphasized that the readily available pools vs time can be in most instances described by a first-order exponential equation, thus an asymptotical value is approached. Consequently, the leaching assays can be performed without attaining chemical equilibrium. Enhancement factors and detection limits were 10.2 and 18.8, and 0.40 and 0.37 mg kg(-1) for ametryn and atrazine, respectively. The automatic method features good repeatability for leaching tests (r.s.d.: 11.8-10.2% for sandy and 3.7-6.2% for clayey soil). Reliable data, demonstrated with relative recoveries in the soil leachates ranging from 86 to 104%, were achieved in less than 35 min, thus avoiding the need for up to 24 h as recommended by standard leaching methods. (C) 2016 Elsevier B.V. All rights reserved.