Characterization of Pyrogenic Black Carbon by Desorption Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Abstract

We present a new method for molecular characterization of intact biochar directly, without sample preparation or pretreatment, on the basis of desorption atmospheric pressure photoionization (DAPPI) coupled to Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. Conventional ionization methods (e.g., electrospray or atmospheric pressure photoionization) for characterization of natural organic matter have limited utility for the characterization of chars due to incomplete solubility in common solvents. Therefore, direct ionization techniques that do not require sample dissolution prior to analysis are ideal. Here, we apply DAPPI FTICR mass spectrometry to enable the first molecular characterization of uncharred parent oak biomass and after combustion (250 °C) or pyrolysis (400 °C). Parent oak is primarily composed of cellulose-, lignin-, and resin-like compounds. Oak combusted at 250 °C contains condensed aromatic compounds with low H/C and O/C ratios while retaining compounds with high H/C and O/C ratios. The bimodal distribution of aromatic and aliphatic compounds observed in the combusted oak sample is attributed to incomplete thermal degradation of lignin and hemicellulose. Pyrolyzed oak constituents exhibit lower H/C and O/C ratios: approximately three-quarters of the identified species are aromatic. DAPPI FTICR MS results agree with bulk elemental composition as well as functional group distributions determined by elemental analysis and solid state (13)C NMR spectroscopy. Complete molecular characterization of biomass upon thermal transformation may provide insight into the biogeochemical cycles of biochar and future renewable energy sources, particularly for samples currently limited by solubility, separation, and sample preparation.

An ultrahigh‐resolution mass spectrometry index to estimate natural organic matter lability

“…The concept of an FTICRMS molecular lability boundary (MLB) is based on our current understanding of van Krevelen diagrams, incorporating chemical information depicted by various H/C and O/C ratios and the relative boundaries of each chemical class region (Figs. 1(a)–1(f)) . Chemical class regions from van Krevelen diagrams are used to depict NOM qualitative characterizations of molecular data that comprise ultrahigh‐resolution FTICR mass spectra, and the same general classes were used to consistently compare the NOM quality across all samples.…”

Production and Composition of Pyrogenic Dissolved Organic Matter From a Logical Series of Laboratory-Generated Chars

“…This method does not target aliphatic or other non-condensed compounds in pyDOM, as they likely do not form BPCA compounds upon nitric acid oxidation. Aliphatic and O-containing components are likely to be more soluble than the condensed aromatic fraction, thus may represent a large portion of pyDOM, as directly identified using FTICR-MS (Podgorski et al, 2012;Ward et al, 2014). It is also unclear if the BPCA method quantifies pyC, exclusively.…”

Polycyclic aromatic hydrocarbons and volatile organic compounds in biochar and biochar‐amended soil: a review

“…Clough et al (2010) also confirmed the presence of VOCs in biochar using solid-phase micro-extraction (SPME) and GC-MS methods. Ultrahigh-resolution mass spectrometric techniques, such as Fourier transform ion cyclotron mass spectrometry (FT-ICR MS), have also been adapted for direct molecular characterization of biochar materials (Podgorski et al, 2012). Although headspace instrumentation has been reported as an ideal tool for the determination of sorbed VOCs (Bernardo et al, 2010;Spokas et al, 2011), current methodologies are not reliable enough for quantitative estimation of VOCs in biochar.…”