Solid-phase extraction and capillary electrophoresis determination of phenols from soil after alkaline CuO oxidation

Alkaline CuO oxidation has been used on molecular-level analyses of phenols from organic matter in the last decades. This method, originally developed by Hedges and Ertel [Hedges, J.I., Ertel, J.R., 1982. Characterization of lignin by gas capillary chromatography of cupric oxide oxidation products. Anal. Chem. 54, 174-178] has several drawbacks that have limited is wider utilization. In this paper, we propose a modification of the method using a solid-phase extraction (SPE) instead of a liquid-liquid extraction. The SPE procedure using C18 cartridges was optimized to obtain high recoveries. The sequential elution with acetonitrile and methanol was found to be the most appropriate procedure. Recoveries of the 12 phenols in individual standard solutions ranged from 84% to 113% with relative standard deviation (RSD) lower than 12%. Experiments with a mixed standard solution highlighted the competition between the different phenols for the adsorbing sites. Recoveries decreased with polarity, reaching 30% for p-hydroxybenzoic acid when present at a concentration of 2.5 x 10(-3)M. A sample soil subjected to a CuO oxidation was used to test the reproducibility of the SPE method and good results were achieved, RSD ranged between 0.4% and 28.3%. The performance of the CE method was also evaluated by correlation coefficients (higher than 0.9920), linearity (higher than 99.902%) and limit of detection (ranging from 2.64 x 10(-6) to 1.25 x 10(-5)M). SPE procedure presents several advantages such as fast sample preparation, good recoveries, good accuracy, low sample handling and safety improvement due to reduced solvent/sample exposure and glassware management.