Comparative Study of Solid-Phase Extraction and Liquid-Liquid Extraction for the Reliable Quantification of High Value Added Compounds from Oxidation Processes of Wood-Derived Lignin

Technologies and processes for lignocellulosic conversion in biorefineries are emergent subjects of research for which a reliable analysis of raw materials and quantification of yields of reaction products are required. This paper presents the development of an analytical method, using solid-phase extraction (SPE), for application to the reaction mixture of the oxidation of wood-derived lignin. The aim of the method is to extract the high value added aldehydes for quantification by high-performance liquid chromatography with ultraviolet detection (HPLC-UV). SPE and conventional liquid-liquid extraction (LLE) were evaluated and compared concerning recoveries and precision: (i) solutions of standard phenolic compounds (in alkaline medium and in lignin as matrix) and (ii) real samples and spiked real samples. The presence of lignin in the solutions decreases the recoveries of compounds from about 100% (no lignin) to 91% (for prepared solutions of lignin) and 94% (for real samples). This decrease was clearly evident with the increase of concentration of phenolic compounds in spiked real samples. The recovery averages and precision of SPE were higher than those of LLE and less affected by the presence of lignin. The results gathered and discussed in this work revealed SPE as an alternative to LLE: it is less time-consuming and has higher accuracy and precision for the quantification of phenolic compounds as reaction products of lignin oxidation.