Graphite Sheet-Assisted Laser Desorption Ionization-Mass Spectrometry for Small Organic Compound Analysis

Carbon-based nanopowders have been used as ionization materials for laser desorption ionization-mass spectrometry (LDI-MS) and are very efficient at detection in low m/z regions. In this study, we aimed to develop a new sheet-type graphite material that possessed a randomly grooved nanostructured surface consisting of developed sp2-conjugated atomic carbon to facilitate the desorption/ionization of small compounds in LDI-MS. The graphite sheet exhibited higher UV absorption and provided higher ionization efficiency and survival yield in the LDI-MS detection of a thermometer ion, 4-chloro-benzopyridinium, than those of highly oriented graphite plates. These properties demonstrate that the present graphite sheet is suited for use as an LDI-MS material. Graphite sheet-assisted LDI-MS successfully detected various substances, including amino acids, peptides, and polyethylene glycol polymers, with higher ion intensities and less noise than those associated with conventional organic matrix-assisted LDI-MS (MALDI-MS). Furthermore, graphite sheet-assisted LDI-MS analysis provided more peaks (252 peaks) derived from soy sauce than those obtained by MALDI-MS (36 peaks) and required fewer preparation processes (dilution and air-dried) compared with previously established graphite carbon black-assisted LDI-MS (171 peaks) in the positive mode. This study demonstrates that graphite sheet-assisted LDI-MS has the potential for small organic compound analyses in the biomedical and food science fields.

The occurrence of pristine and functionalized fullerenes as constituents of airborne aerosols

We investigated if pristine and functionalized fullerenes could be actual constituents of fine atmospheric aerosols. Comprehensive profiles of fullerenes from 1 µL extracts were made through matrix laser desorption ionization Time-of-Flight Mass Spectrometry (MALDI-MS) within a few minutes. The ion with m/z 720, corresponding to [C₆₀]^-•, was identified as fullerene after 1 µL of α-cyano-4-hydroxycinnamic acid matrix solution was spotted over the dried extracts. The ions with the m/z corresponding to C₇₀, C₇₆, C₈₄, C₁₀₀, C₁₁₈, C₁₂₈, and C₁₃₀ were also attributed to other fullerene species detected within the samples. The ion m/z 878 was found to be the fullerene derivative diethyl methano[60]fullerene dicarboxylate. Since ions of fragmented fullerene molecules were not detected even at high laser energies, we considered the fullerenes' occurring as original constituents of real atmospheric particle matrices instead of being formed as artifacts of the laser action on samples. Therefore, this protocol would be helpful in the understanding of the distribution of either pristine or functionalized fullerenes in the environment and their participation in atmospheric chemistry under typical conditions, as well as its application in vitro and in vivo (eco)toxicity studies.

Impact of Asphaltene Precipitation and Deposition on Wettability and Permeability

Asphaltene precipitation and deposition have been a formation damage problem for decades, with the most devastating effects being wettability alteration and permeability impairment. To this effect, a critical look into the laboratory studies and models developed to quantify/predict permeability and wettability alterations are reviewed, stating their assumptions and limitations. For wettability alterations, the mechanism is predominantly surface adsorption, which is controlled by the asphaltene contacting minerals as they control the surface chemistry, charge, and electrochemical interactions. The most promising wettability alteration evaluation techniques are nuclear magnetic resonance, ζ potential, and the use of high-resolution microscopy. The integration of such techniques, which is still missing, would reinforce the understanding of asphaltene interaction with rock minerals (especially clays), which holds the key to developing a strategy for modeling wettability alteration. With regard to permeability impairment, surface deposition, pore plugging, and fine migration have been identified as the dominant mechanisms with several models reporting the simultaneous existence of multiple mechanisms. Existing experimental findings showed that asphaltene deposition is non-uniform due to mineral distribution which further complicates the modeling process. It also remains a challenge to separate changes due to adsorption (wettability changes) from those due to pore size reduction (permeability impairment).

Asphaltene-Derived Metal-Free Carbons for Electrocatalytic Hydrogen Evolution

The design of new and improved catalysts is an exciting field and is being constantly improved for the development of economically, highly efficient material and for the possible replacement of platinum (Pt)-based catalysts. In this, carbon-based materials play a pivotal role due to their easy availability and environment friendliness. Herein, we report a simple technique to synthesize layered, nitrogen-doped, porous carbon and activated carbons from an abundant petroleum asphaltene. The derived nitrogen-doped carbons were found to possess a graphene-like nanosheet (N-GNS) texture with a significant percentage of nitrogen embedded into the porous carbon skeleton. On the other hand, the activated porous carbon displayed a surface area (SA) of 2824 m²/g, which is significantly higher when compared to the nitrogen-doped carbons (SA of ∼243 m²/g). However, the nonactivated N-GNS were considered as an attractive candidate due to their high electrochemical active surface area, the presence of a mixture of porous structures, uniform layers, and effective doping of nitrogen atoms within the carbon matrix. Importantly, the hydrogen evolution reaction activity of the derived N-GNS sample illustrates a significant catalytic performance when compared to that of other nonfunctionalized carbons. Our current finding demonstrates the possibility of converting the asphaltene wastes into a high-value-functionalized porous carbon for catalytic applications.

Occurrence of C60 and related fullerenes in the Sava River under different hydrologic conditions

The presence of nanomaterials in the environment has caught the attention of the scientific because of the uncertainties in their fate, mobility and potential toxic effects. However, few studies have determined experimentally their concentration levels in aquatic systems up to date, which complicates the development of an adequate risk assessment. In the present study, the occurrence of ten fullerenes has been assessed in the Sava River (Southeastern Europe): 27 freshwater samples and 12 sediment samples from 12 sampling points have been analysed during two sampling campaigns. C₆₀ was the most ubiquitous fullerene, with concentrations of 8 pg/l-59 ng/l and 108-895 pg/g_dw in water and sediments, respectively. Statistically significant differences existed between the levels in 2014 and 2015, which has been attributed to the extreme hydrologic conditions (severe floods and drought, respectively). C₇₀ fullerene has been detected in most of the samples and the fullerene derivatives [6,6]-phenyl C₆₁ butyric acid methyl ester and N‑methyl fulleropyrrolidine have been detected eventually, which highlights that nanotechnology research and development activities are responsible for emitting these emerging contaminants to the environment. The role of diverse potential anthropogenic sources (including oil refinery, general industrial activity, river navigation, urban emissions and nanotechnology) is discussed.

Evaluation of Thin-Layer Chromatography-Laser Desorption Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometric Imaging for Visualization of Crude Oil Interactions

A light oil was separated into four chromatographic fractions that serve as proxy for SARA fractions. The fractions were (semi)quantified on a rod by TLC-flame ionization detection and characterized on a plate with laser desorption ionization-mass spectrometry imaging (TLC-LDI-MS). Comparisons of (semi)quantitative TLC-FID and qualitative TLC-LDI-MS results showed that LDI-MS was most sensitive for detection of molecules in the polar P1 fraction, and, to some extent, for the aromatics fraction, while no signal was observed for the most polar P2 and saturates fractions. Based on these results, limits of the compositional space, as observed by the laser ionization technique, were evaluated. The molecular speciation between and within the spots of the aromatics and the P1 fractions were analyzed and interpreted in terms of oil-SiO₂ versus oil-solvent interactions, as a function of molecular characteristics such as DBE, aromaticity (H/C ratio), heteroatom content, degree of alkylation, and shielding of heteroatoms. In addition, the high oil loading resulted in an interesting bifurcation of the aromatics spot, which implies that oil-oil interactions can be enforced and studied in the TLC model system.

Pulse laser-induced fragmentation of carbon quantum dots: a structural analysis

Carbon quantum dots (CQDs) have attracted enormous interest in recent years owing to their low cytotoxicity, excellent biocompatibility and strong fluorescence. They have been successfully employed in sensor, bio-imaging, and drug carrier applications. A complete understanding of their core-surface structure is essential for tuning their physical and chemical properties for various applications. Conventional characterizations of CQDs are conducted with electron microscopy or spectroscopy, such as transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. However, these techniques cannot fully resolve the core-surface structure of CQDs. In this study, we attempt to analyze the structures of CQDs by laser desorption/ionization mass spectrometry (LDI-MS) using three model CQDs synthesized from citric acid (CA-CQDs), diammonium citrate (AC-CQDs) and spermidine trihydrochloride (Spd-CQDs). Both CA-CQDs and AC-CQDs produced anionic carbon cluster ions ([C_n]^-, n = 4-9) during the laser desorption/ionization process. Additionally, AC-CQDs produced fragments containing C, N, and O that appeared at m/z values of 41.999, 91.015, and 107.008, which were identified by ¹⁵N isotopes as [CNO]^-, [CH₃N₂O₃]^-, and [CH₃N₂O₄]^-, respectively. By contrast, subjecting Spd-CQDs to the same analysis did not yield carbon cluster ions ([C_n]^-); instead, strong chlorine-associated ions with a unique isotopic pattern were observed, strongly implying that Spd-CQDs contain chlorine. The lack of carbon cluster ion formation in nitrogen- and chlorine-doped Spd-CQDs indicates that nitrogen and chlorine are abundantly and homogenously doped in the CQDs. We also found a shot-dependent fragmentation behavior for AC-CQDs that produces nitrogen- and oxygen-containing ions and carbon cluster ions ([C_n]^-) during initial fragmentation of the surface, with a gradual destruction of the nanocrystalline carbon core after additional shots. These results suggest that LDI-MS can be used as a tool for analyzing the core-surface structure of CQDs, particularly when it contains a heteroatom doped carbon core with various surface functional groups containing nitrogen, oxygen and halogens.