RESUMO
Lignin was isolated from wheat straw via organosolv process and further transferred to monophenolic compounds via oxidative conversion. Wheat straw lignin (WSL) with purity at 91.4 wt% was acquired in the presence of heterogeneous and recyclable catalyst of Amberlyst-45. WSL was characterized by infrared spectrometer (IR), nuclear magnetic resonance spectroscopy (NMR) including 1H NMR and 13C NMR spectra. The results showed that WSL possesses typical syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) units, and it is mainly composed of S and G units. The product distribution was dependent on the composition of WSL. Derivatives from S and G units were found to be the main products. The oxidative conversion of WSL was performed by varying oxidant and catalyst. Both the formation of monophenolic compounds and aromatic aldehydes were enhanced by combining oxidants and catalysts. The composite catalyst composed of NaOH/NaAlO2 was effective for the oxidation of WSL in the presence of nitrobenzene and atmospheric pressure air. The total yield of monophenolic compounds reached up 18.1%, and yields at 6.3 and 5.7% for syringaldehyde and vanillin were achieved, respectively.
RESUMO
A method for the direct determination of trace lead in chestnut by Graphite Furnace Atomic Absorption Spectrometry (GFAAS) with slurry sampling was developed in the present paper. Ammonium ortho-phosphate was used as a matrix modifier. The effects of slurry preparation, particle size of sample, matrix modifier, ashing temperature, atomization temperature, and common coexisting components on the determination of lead were studied. Under the optimized operating conditions, the detection limit, the relative standard deviation (RSD), and the recoveries of standard addition for this method were 0.47 ng x mL(-1), 6.1% (n = 11) and 90%-106%, respectively.
