Critical Evaluation of Adsorption–Desorption Hysteresis of Heavy Metal Ions from Carbon Nanotubes: Influence of Wall Number and Surface Functionalization

Single‐, double‐, and multi‐walled carbon nanotubes (SWCNTs, DWCNTs, and MWCNTs), and two oxidized MWCNTs with different oxygen contents (2.51 wt % and 3.5 wt %) were used to study the effect of the wall number and surface functionalization of CNTs on their adsorption capacity and adsorption–desorption hysteresis for heavy metal ions (Ni^II, Cd^II, and Pb^II). Metal ions adsorbed on CNTs could be desorbed by lowering the solution pH. Adsoprtion of heavy metal ions was not completely reversible when the supernatant was replaced with metal ion‐free electrolyte solution. With increasing wall number and amount of surface functional groups, CNTs had more surface defects and exhibited higher adsorption capacity and higher adsorption–desorption hysteresis index (HI) values. The coverage of heavy metal ions on the surface of CNTs, solution pH, and temperature affect the metal ion adsorption–desorption hysteresis. A possible shift in the adsorption mechanism from mainly irreversible to largely reversible processes may take place, as the amount of metal ions adsorbed on CNTs increases. Heavy metal ions may be irreversibly adsorbed on defect sites.     

Headspace stir bar sorptive extraction followed by thermal desorption and gas chromatography with mass spectrometry to determine musk fragrances in sludge samples without sample pretreatment

A direct, simple and solvent‐free method based on headspace stir bar sorptive extraction and thermal desorption gas chromatography with mass spectroscopy was developed to determine 13 musk fragrances (six polycyclic musks, three nitro musks and four macrocyclic musks) in sludge without sample treatment. The optimal headspace stir bar sorptive extraction conditions were achieved when a polydimethylsiloxane stir bar was exposed for 45 min in the headspace of a 10 mL vial filled with 100 mg of sludge mixed with 0.2 mL of water stirred at 750 rpm at 80°C. The stir bar was then desorbed in the thermal desorption gas chromatography and mass spectrometry system, obtaining limits of detection between 5 and 30 ng/g. The method applicability was tested with sewage sludge from two urban wastewater treatment plants and from a potable water treatment plant. Results showed galaxolide and tonalide to be the most abundant musk fragrances found in wastewater treatment plants with maximal concentrations of 9240 and 7500 ng/g, respectively. Maximum concentration levels between 35 and 635 ng/g were found for musk ketone, musk moskene, traseolide, phantolide and celestolide in this kind of samples. Concentrations below the limits of quantitation of phantolide, galaxolide, tonalide and musk ketone were found in sludge from a potable water treatment plant.     

Simultaneous effect of carbon and water on NOx adsorption on a stabilized Pt–Ba/Al2O3 catalyst

The influence of the presence of H₂O on the contact between carbon, used as model soot, and a model four-way catalyst (1% Pt–10% BaO/Al₂O₃) was investigated. NO_x adsorption/TPD cycles at 300 °C together with XRD, XPS and DRIFTS characterizations showed that only surface nitrate species are destabilized by the carbon present in the catalytic bed, leading to a decrease of the NO_x storage capacity and carbonate species formation. In another way, injection of water in the reactive gas flow decreases also the NO_x storage capacity of the catalyst, but promotes the formation of stable nitrate species. A non-cumulative effect of carbon and water was observed. It was proposed that a competition between the destabilization, by carbon, of weakly bonded surface nitrate species and the enhancement of bulk nitrate species formation in the presence of water occurs.     

Modern mass spectrometry in the characterization and degradation of biodegradable polymers

In the last decades, the solid-waste management related to the extensively growing production of plastic materials, in concert with their durability, have stimulated increasing interest in biodegradable polymers. At present, a variety of biodegradable polymers has already been introduced onto the market and can now be competitive with non biodegradable thermoplastics in different fields (packaging, biomedical, textile, etc.). However, a significant economical effort is still directed in tailoring structural properties in order to further broaden the range of applications without impairing biodegradation. Improving the performance of biodegradable materials requires a good characterization of both physico-chemical and mechanical parameters. Polymer analysis can involve many different features including detailed characterization of chemical structures and compositions as well as average molecular mass determination. It is of outstanding importance in troubleshooting of a polymer manufacturing process and for quality control, especially in biomedical applications. This review describes recent trends in the structural characterization of biodegradable materials by modern mass spectrometry (MS). It provides an overview of the analytical tools used to evaluate their degradation. Several successful applications of MALDI-TOF MS (matrix assisted laser desorption ionization time of flight) and ESI MS (electrospray mass spectrometry) for the determination of the structural architecture of biodegradable macromolecules, including their topology, composition, chemical structure of the end groups have been reported. However, MS methodologies have been recently applied to evaluate the biodegradation of polymeric materials. ESI MS represents the most useful technique for characterizing water-soluble polymers possessing different end group structures, with the advantage of being easily interfaced with solution-based separation techniques such as high-performance liquid chromatography (HPLC).     

Experimental validation of an effective carbon number-based approach for the gas chromatography–mass spectrometry quantification of ‘compounds lacking authentic standards or surrogates’

For the quantitative analysis of ‘compounds lacking authentic standards or surrogates’ (CLASS) in environmental media, we previously introduced an effective carbon number (ECN) approach to develop an empirical equation for the prediction of their response factor (RF). In this research, a series of laboratory experiments were carried out to benchmark the reliability of an ECN approach for sorbent tube/thermal desorption/gas chromatography (GC)/mass spectrometry (MS) applications. First, the ECN values were determined using external calibration data from 25 reference volatile organic compounds (VOCs) using two MS dectectors (quadrupole (Q) and time-of-flight (TOF)). Then, a certified standard mixture of 54 VOCs was analyzed by each system as a simulated unknown sample. The analytical bias, assessed in terms of percentage difference (PD) between the certified and ECN-predicted mass values, averaged 19.2 ± 16.1% (TOF-MS) and 28.2 ± 27.6% (Q-MS). The bias using a more simplified carbon number (CN)-based prediction increased considerably, yielding 53.4 ± 53.3% (TOF-MS) and 61.7 ± 81.3% (Q-MS). However, the bias obtained using the ECN-based prediction decreased significantly to yield average PD values of 9.84 ± 7.28% (TOF-MS) and 16.8 ± 8.35% (Q-MS), if the comparison was limited to 26 (out of 54) VOCs with CN ≥ 4 (i.e., 25 aromatics and hexachlorobutadiene).     

Zirconium silicate assisted removal of residual proteins after organic solvent deproteinization of human plasma,enhancing the stability of the LC–ESI-MS response for the bioanalysis of small molecules

An efficient blood plasma clean-up method was developed, where methanol protein precipitation was applied, followed by zirconium silicate assisted exclusion of residual proteins. A strong binding of zirconium (IV) silicate to the proteins enabled the elimination of remaining proteins after solvent deproteinization through a rapid solid-phase extraction (SPE) procedure. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI/TOF MS) was used for monitoring the proteins during clean-up practice applied to human plasma samples. The proteins were quantified by colorimetric detection using the bicinchoninic acid (BCA) assay. The presented analytical strategy resulted in the depletion of >99.6% proteins from human plasma samples. Furthermore, high-performance liquid chromatography hyphenated to diode-array and electrospray ionization mass spectrometric detection (HPLC–DAD/ESI MS) was applied for qualitative and quantitative analysis of the caffeoylquinic acids (CQAs) and their metabolites in human plasma. The procedure demonstrated high recoveries for the standard compounds spiked at different concentrations. Cynarin and chlorogenic acid were recovered in the range of 81–86% and 78–83%, respectively. Caffeic acid was extracted in the excess of 89–92%, while ferulic acid and dihydroxyhydrocinnamic acid showed a recovery of 87–91% and 92–95%, respectively. The method was partially validated in accordance with FDA-Industry Guidelines for Bioanalytical Method Validation (2001). The presented scheme improves the clean-up efficacy of the methanol deproteinization, significantly reduces the matrix effects and provides a great analytical tool for the isolation of small molecules from human plasma.     

Use of a porous silicon–gold plasmonic nanostructure to enhance serum peptide signals in MALDI-TOF analysis

Small peptides in serum are potential biomarkers for the diagnosis of cancer and other diseases. The identification of peptide biomarkers in human plasma/serum has become an area of high interest in medical research. However, the direct analysis of peptides in serum samples using mass spectrometry is challenging due to the low concentration of peptides and the high abundance of high-molecular-weight proteins in serum, the latter of which causes severe signal suppression. Herein, we reported that porous semiconductor-noble metal hybrid nanostructures can both eliminate the interference from large proteins in serum samples and significantly enhance the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) yields of peptides captured on the nanostructure. Serum peptide fingerprints with high fidelity can be acquired rapidly, and successful discrimination of colorectal cancer patients based on peptide fingerprints is demonstrated.     

Mechanistic aspects of magnetic MgAlNi barium-ferrite nanocomposites enhanced adsorptive removal of an anionic dye from aqueous phase

The mechanistic aspects of improved aqueous removal of methyl orange (MO) dyes using high performance novel magnetic MgAlNi barium-ferrite (MgAlNi-BaFe) ternary double layer hydroxide (LDH) nanocomposites is reported in this study. Detailed surface characterization coupled with kinetic, equilibrium, thermodynamics and regeneration studies were undertaken under different operational conditions of temperature (298–318 K), initial concentration (20–100 mg/L), pH (2–6). The kinetic results show that MO sorption was mainly, associated with pseudo-second order and intra-particular diffusion process. The MO adsorption onto the MgAlNi-BaFe nanocomposites suggests a multi-layered sorption process that is endothermic and spontaneous in nature. The MO adsorption mechanism insight taken in cognizance of FTIR, XRD, pKa, zeta potential, the adsorbates surface functional groups and the adsorbate-adsorbent surface charges interactions suggest involvement of hydrogen bonding and n-π interactions, predominantly via physisorption process (ΔG° = −7.406 to −5.69 kJ/mol). The excellent adsorptive performance of the MgAlNi-BaFe adsorbents for removal of MO from water compared with other magnetic LDH nanocomposites was further elucidated via the MgAlNi-BaFe nanomaterials high rates of regeneration and superior performances for three successive desorption-adsorption cycles. This study demonstrates the high potentials of employing MgAlNi-BaFe nanomaterials for removal of dyes from water and wastewater.     

解析电喷雾质谱法对感冒药中对乙酰氨基酚的快速检测

基于常压质谱的直接、快速、无需样品预处理检测的优势,该文拓展了其在药物质检领域的应用。采用自行搭建的解析电喷雾(DESI)装置,对常用感冒药对乙酰氨基酚片进行快速质谱检测,无需样品预处理,直接获得药片中有效成分的分子结构信息。为克服基质差异对定量分析的影响,以淀粉为基质构建对乙酰氨基酚模拟药片,在优化的基础上进行定量实验。针对实际药片中高浓度对乙酰氨基酚检测的需要,研究了其在较高浓度范围的定量关系,结果显示,方法对0.35~4.52 mg/mm^2范围内的对乙酰氨基酚具有较好的线性关系(r^2=0.9982),定量下限为1.903 ng/mm^2,检出限为0.237 ng/mm^2,加标回收率为102%~114%。对3种市售的对乙酰氨基酚片进行直接检测,与厂家提供的标准数据相比,相对标准偏差(RSD)为7.2%~12%,表明方法具有较好准确度。该工作很好地证明了DESI-MS在药品快检中的优势,从而为药品质检提供了潜在的高效、可靠的检测手段。     

新型表面辅助激光解吸附/离子化质谱基质及其在生物检测中的应用

表面辅助激光解吸附/离子化质谱(Surface-assisted laser desorption/ionization mass spectrometry,SALDI-MS)是一种利用无机纳米粒子或纳米结构表面作为基质,辅助待测分子的解吸附和离子化的质谱技术。由于其具有灵敏度高、耐盐性好、操作简便、重现性好、检测通量高等优势,已经被广泛应用于食品安全、环境监测、生命科学等诸多领域。该文总结了近5年来,SALDI基质材料(金属及金属氧化物材料、碳材料、硅材料、金属有机骨架化合物材料等)的最新研究进展及其在生物检测领域中的应用,并对SALDI-MS基质材料的发展及应用进行了展望。