Abstract
Levoglucosan is a thermal decomposition product of cellulose in particulate matter. δ13C value of levoglucosan could be used in studying the combustion mechanisms and chemical pathways. In order to introduce a minimum number of carbon atoms, based on the stereostructure of levoglucosan, a two-step derivatization method with methylboronic acid and MSTFA was developed and carefully optimized. The recommended reaction temperature is 70°C; the reaction time is 60 min for MBA and 120 min for MSTFA derivatization; and the molar ratio of levoglucosan : MBA : MSTFA is 1 : 1: 100 and 1 : 1: 120 and the reagent volume ratio of MSTFA : pyridine is between 1 : 3 and 1 : 4. The developed method achieved excellent reproducibility and high accuracy. The differences in the carbon isotopic compositions of the target boronate trimethysilylated derivative between the measured and calculated ranged from 0.09 to 0.36‰. The standard deviation of measured δ13C value of levoglucosan was between 0.22 and 0.48‰. The method was applied to particle samples collected from the combustion of cellulose at four different temperatures. δ13C values of levoglucosan in particle samples generated from a self-made combustion setup suggesting that combustion temperature play a little role on isotope fractionation of levoglucosan, although 13C enriched in levoglucosan during the combustion process.
Highlights
Levoglucosan (1.6-anhydro-β-D-glucopyranose) is a thermal decomposition product of cellulose and hemicellulose in biomass at temperatures above 300°C [1]
Stable carbon isotope analysis is a valuable tool, because the stable isotope ratio of organic compounds depends on the isotope composition of the source, environmental conditions, and specific chemical pathways and mechanisms that lead to the formation of the compound. ere have been reports measuring directly the δ13C values of levoglucosan as one of pyrolysis products of sucrose [2] and cellulose [5] using pyrolysis gas chromatography/isotope ratio mass spectrometry and levoglucosan in biomass burning aerosols by thermal desorption-2 dimensional gas chromatography/ isotope ratio mass spectrometry [6]
Four standard levoglucosan with different δ13C values were used to determine the feasibility of the method. e isotopic fractionation effects were discussed based on the comparison of determined δ13C values and calculated values according to the stoichiometric mass balance. e method was applied to the particulate matter generated from combustion of microcrystalline cellulose at four temperatures
Summary
Levoglucosan (1.6-anhydro-β-D-glucopyranose) is a thermal decomposition product of cellulose and hemicellulose in biomass at temperatures above 300°C [1]. Ere have been reports measuring directly the δ13C values of levoglucosan as one of pyrolysis products of sucrose [2] and cellulose [5] using pyrolysis gas chromatography/isotope ratio mass spectrometry and levoglucosan in biomass burning aerosols by thermal desorption-2 dimensional gas chromatography/ isotope ratio mass spectrometry [6]. Methylboronic acid (MBA) has a planar, trigonal structure with the O-O distance 2.4 A (Figure 1(a)). It contains only one carbon atom and readily condenses with two vicinal cisdiols and, has been used to determine natural 13C. Two OH groups of MBA might not react with levoglucosan Such distance could be adequate for the formation of a six-membered cyclic boronate ring, considering that the even longer O-O distance intrans-1, 2-dioIs (3.4 A ) can react with boronic acid [14]. Four standard levoglucosan with different δ13C values were used to determine the feasibility of the method. e isotopic fractionation effects were discussed based on the comparison of determined δ13C values and calculated values according to the stoichiometric mass balance. e method was applied to the particulate matter generated from combustion of microcrystalline cellulose at four temperatures
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