A Semiautomatic Module for the Direct Leaching and Determination of Sixteen Phenols in Agricultural Soils

A module for the continuous extraction and preconcentration of phenol compounds from soils was developed which comprised a soil extraction unit, a preconcentration unit, and an interface between the two. The extraction fluid flows were controlled by multiport rotary valves and were driven by peristaltic pumps and by compressed nitrogen. The interface plays a crucial role in changing the pH and homogenizing the sample before preconcentration; in addition the sample volume was controlled at the interface. Spiked uncontaminated soils were prepared 2 months before treatment in order to simulate weathering and allow for the occurrence of analyte−matrix interactions. Soil extractions were done with alkaline aqueous solutions and solid−sorbent preconcentration in an acid medium, using XAD-2 as sorbent. Soil samples (0.1−10 g) containing 50−5000 ng/g phenols were analyzed with a high precision (4−7%). Average recoveries of 60−80% were achieved, except for 2- tert -butyl-4-methylphenol, the mean recovery for which was rather poor (9%). The adsorption−desorption of phenols in agricultural soils was evaluated, and their clay mineral and organic matter contents were found to affect the recovery of alkylphenols to a different extent than those of chlorophenols and nitrophenols.