DDT degradation during enhanced solid-liquid extractions

Analysis of p,p′-DDT in solid environmental samples, like soil or sediment, requires monitoring the breakdown of this insecticide during sample preparation and measurement, which produces mainly p,p′-DDD and p,p′-DDE. The occurrence of matrix-enhanced p,p′-DDT degradation during GC injection is a well-known phenomenon; careful cleaning and pre-treatment of the GC injection port enables for an overcoming of this problem. Modern solid-liquid extraction methods apply high temperatures and/or pressures to enhance the extraction kinetics and diffusion rates of the target compounds from the solid matrix. Due to the parameters, high temperature and catalytic surface, DDT could break down during enhanced solid-liquid extraction comparable to the degradation process during GC injection. In the present study a performance evaluation by an experimental design of microwave-assisted extraction in closed vessels, pressurized-liquid extraction and fluidized-bed extraction with standard solutions of p,p′-DDT and with a quality control material was carried out. In order to identify the effect of matrix-enhanced DDT degradation during solid-liquid extraction a careful analytical protocol using isotope labelled standards was developed. At high temperatures matrix-enhanced degradation could be observed during all three investigated extraction methods. This result might have important implications on the resultant interpretations of environmental degradation of DDT.