Ultrasound-assisted Extraction Method for Element Determination in Lignocellulosic Biomass

In this work, a sample preparation method based on ultrasound-assisted extraction (UAE) for the determination of Al, Ba, Ca, Fe, K, Mg, Mn, Na, P, Sr, and Zn in lignocellulosic biomasses (sugarcane bagasse, eucalyptus wood residues, and pine wood residues) was evaluated. Reference values were achieved following the EN ISO 16967, which was based on a microwave-assisted wet digestion sample preparation method for further element determination by inductively coupled plasma optical emission spectrometry (ICP OES). The optimizations for the proposed UAE method were performed using 250 mg of sugarcane bagasse sample, where the ultrasonic bath frequency (25, 35, 37, 45, 80, and 130 kHz), and acoustic amplitude (50, 70 and 100%) were evaluated. After selecting the most efficient extractant solvent (20 mL of 1 mol L-1 of H2O2, HNO3, H2SO4, H2O, or CH2O2), the extraction temperature (20, 50, or 70 ºC) and time (15, 30, or 40 min) were evaluated. The most efficient extraction condition using the UAE method employed 45 kHz (70% amplitude), 20 mL of 1 mol L-1 of H2SO4, and 50 °C for 30 min. The optimized UAE was used for extraction and subsequent element determination in residues of pine wood and eucalyptus wood. Although poor recoveries were observed for Al, Ba, and Fe (lower than 75%), the results for Ca, K, Mg, Mn, Na, P, Sr, and Zn were in agreement (Student t-test, 95% confidence level) with those obtained by EN ISO 16967. Therefore, the proposed UAE method proved to be efficient for the determination of most of the evaluated elements in lignocellulosic biomasses with different matrix complexity, employing milder extraction conditions and diluted reagents.