Hydrolysis study and extraction of spiroxamine from soils of different physico-chemical properties

Spiroxamine, 8-(1,1-dimethylethyl)-N-ethyl-N-propyl-1,4-dioxa-spiro [4.5] decane-2-methanamine, is a novel broad-spectrum fungicide from the new class of spiroketalamines widely used in cereals and grapes. In this paper, the hydrolysis of the spiroxamine active substance has been investigated and the extraction procedure from soil samples has been optimized. The progress of degradation in water at a wide pH range (4-14), was continuously monitored by means of reversed phase LC-ESI-MS/MS in the positive ionization mode during 90 d incubation experiment. To establish the degradation kinetics, water solutions were incubated by triplicate in the dark under controlled temperature (20+/-2 degrees C) and the spiroxamine remaining concentration was determined. Pesticide metabolites such as desethyl, despropyl and N-oxide spiroxamine were not detected at significant amounts in all tested conditions and the degradations followed first-order kinetics (r(2)>or=0.979). The faster degradation was observed at both pH 4 and 14 with half-life times of 37 and 10 d, respectively. On the other hand, the spiroxamine fungicide has been determined in two types of soil (silt loam and sandy loam) at different spiked levels. At the level of the highest spiroxamine application rate for agricultural crops (750 g a.i. ha(-1)), recoveries higher than 96.0% were obtained, showing the effectiveness of the proposed methodology.