On-line Mass Spectrometry Research Articles

Aqueous-Based Post-Treatment of Li- and Mn-Rich Ncm

To achieve lithium-ion batteries with high energy density at competitive prices for automotive and large-scale applications, cathode active materials (CAMs) based on Li- and Mn-rich NCMs (LMR-NCMs), like Li1.14(Ni0.26Co0.14Mn0.60)0.86O2, are promising candidates.[1] However, LMR-NCMs still suffer from high gassing, particularly during cell formation, and detrimental voltage and capacity fading over their cycle life.[2,3] Different approaches can be utilized to try to mitigate these issues, such as the use of electrolyte additives, novel material designs (compositional gradients, etc.), or post-treatments.[4–7] In this study, we investigated the effect of a water-based post-treatment of LMR-NCM. It consists of a washing process of the LMR-NCM that results in a partial delithiation of its near-suface region by a lithium/proton ion exchange, while at the same time avoiding transition metal dissolution. A recalcination of this protonated near-surface layer of the LMR-NCM particles results in the formation of a protective spinel-like surface layer. We observed that after this treatment, the gassing during formation is decreased by »10-fold. Furthermore, the cycling performance of graphite/LMR-NCM full-cells is also drastically increased.By conducting on-line electrochemical mass spectrometry (OEMS) measurements, we analyzed the gas evolution of as-received and post-treated LMR-NCMs during the first activation cycle. It is known from the literature that the activation of LMR-NCMs is accompanied by a strong O2 and CO2 evolution during the first charge.[2] As seen in Figure 1, CO2 is evolved simultaneously with O2 from Li/LMR-NCM half-cells, prepared with untreated, as-received LMR-NCM (as-received, black line). With post-treated LMR-NCM, both CO2 and O2-evolution during the activation cycle are reduced by »10-fold (post-treated, green line). Only a small amount of the first-charge capacity (<10%) is lost due to the post-treatment, as seen in Figure 1a, reflecting the slight extent of delithiation that is part of the post-treatment.As will be shown, cycling tests of graphite/LMR-NCM full-cells with a post-treated LMR-NCM reveal a greatly increased cycling stability in comparison to cells with an as-received material. Using TGA-MS, XPS and ICP-OES, we further elucidate the beneficial mechanism of the here developed water-based post-treatment.

Spatially Resolved Operando X-Ray Absorption Spectroscopy in NCA/Graphite to Quantify the Potential-Dependent Transition Metal Dissolution and Its Effect on Capacity Fading

Layered transition metal oxides like NCAs (LiNixCoyAlzO2, with x+y+z=1) and NCMs (LiNixCoyMnzO2, with x+y+z=1) are used as cathode active materials (CAMs) for high energy Li-ion batteries due to their high capacity. However, at high upper cut-off potentials, those CAMs suffer from structural instabilities, resulting in severe capacity fading and thus limiting the accessible capacity that can be obtained. Possible causes for the capacity fade at high cut-off potentials and high state-of-charge (SOC) include the (electro)chemical oxidation of the electrolyte oxidation and transition metal (TM) dissolution from the CAM surface.1 Furthermore, layered TM-oxides are known to release lattice oxygen from the near-surface region at high SOC (i.e., at ≈80% SOC when referenced to the total amount of lithium), resulting in reactive oxygen species that induce electrolyte oxidation and HF formation.2 This release of lattice oxygen results in a surface reconstruction from the pristine layered structure to a more resistive spinel- or rocksalt-like structure, thereby inducing an impedance build-up on the cathode. Diffusion of dissolved transition metals to the anode and their subsequent deposition on the anode active material particles can also have a severe effect on cell aging, as the accumulation of metal species on the graphite anode has shown to catalyze the degradation of the protective anode solid/electrolyte interphase (SEI), eventually resulting in the loss of active lithium and in an anode impedance growth. Since the dissolution of manganese is considered to have the most detrimental effect on the anode SEI compared to cobalt and nickel,3 manganese-free NCAs (e.g., LiNi0.8Co0.15Al0.05O2) might have an advantage over manganese-containing NCMs.In this study, we will examine the potential-dependent dissolution of Ni and Co in NCA/graphite cells using operando XAS, and compare it to the potential-dependent dissolution of Ni, Co, and Mn from LiNi0.6Co0.2Mn0.2O2 (NMC622) that we had determined previously by operando XAS.4 Owing to the specially designed geometry of the operando XAS cell,5 we can spectroscopically access and independently investigate the concentration and oxidation state of transition metals, both dissolved in the electrolyte and deposited within the graphite anode. This is illustrated for an NCA/graphite cell in Figure 1. We will also examine the effect of lattice oxygen release from NCA on the NCA/graphite full-cell performance by applying different techniques: We employ a three-electrode Swagelok® type T-cell with a gold wire micro reference electrode (µ-GWRE)6 to quantify the anode and the cathode impedance over the course of 100 cycles as a function of the upper cutoff voltage. In addition, on-line electrochemical mass spectrometry (OEMS)7 is applied to detect the onset SOC for the release of lattice oxygen. From these comparisons, we aim to get a detailed understanding about the influence of transition metal dissolution from NCA on capacity fade and cycle life.

Temperature Dependent Formation of the Graphite SEI with Vinylene Carbonate Electrolyte Additive

The charge/discharge efficiency and the cycle life of lithium-ion batteries (LiBs) depends on a large number of competing interfacial processes. Probably the best-known interface in LiBs is the solid-electrolyte-interphase (SEI), which is a passivating layer formed at the negative electrode by electrolyte decomposition during the first cycles.[1–3] Since the SEI stability is a deciding factor with regards to cycle life, understanding and improving the SEI formation process is crucial. In order to yield an effective SEI, commercial battery cells undergo an extensive so-called formation procedure after cell assembly, which generally consist of multiple voltage-holds and current-steps at various temperatures.[4,5] During the first cycles of a LiB, the SEI is generated by the reduction products of the commonly used carbonate-based electrolyte components, such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).[6,7] Additionally, electrolyte additives are commonly added to form an SEI layer with increased cycling stability and reduced irreversible capacity loss during the first cycle.[6,8–10] Among a variety of additives, vinylene carbonate (VC) is the most prominent. Since the reduction of VC initiates at higher reduction potentials compared to alkyl carbonate solvents (e.g., EC), it is reduced preferentially during the first charge and thus strongly affects the SEI composition.[6,11] In the present study we investigated the effect of the formation temperature in a range between 10-60 °C on the performance characteristics of full-cells with a graphite anode (MAGE) and an NCM831205 cathode as well as of MAGE/Li half-cells, both with LP572 (1 M LiPF6 in EC:EMC 3:7wt/wt + 2wt% VC) electrolyte. These include the first-cycle irreversible capacity loss, the negative electrode impedance build-up, the gas evolution during formation, the rate capability, and the cycle life.Employing electrochemical impedance spectroscopy using a µ-reference electrode allowed us to determine the graphite intercalation resistance (R Int), representing the sum of the SEI resistance (R SEI) and of the charge transfer resistance (R CT), after two 0.1C formation cycles at a given temperature. The impedance spectrum was recorded at 25 °C and 40% SOC referenced to 190 mAh/gNCM reversible capacity. As depicted in Figure 1, both R Int of the graphite electrode in the MAGE/NCM83125 full-cell and the first-cycle irreversible Li-loss determined a MAGE/Li half-cell increase with increasing formation temperature.Additionally, on-line electrochemical mass spectrometry (OEMS) was applied to identify and quantify the gaseous reduction products for LP572 in a MAGE/NCM831205 full-cell during one 0.1C formation cycle at different temperatures. As displayed in Figure 1, the relative increase of the total gas evolved, which is the sum of hydrogen, ethylene, carbon monoxide, and carbon dioxide, follows the relative increase of the intercalation resistance. Next to the overall gas amounts, changes in the quantity of the individual gases give insights into the highly temperature dependent reduction mechanisms of VC. Acknowledgement: The authors thank BMW AG for their financial support.

Rapid and ultra-trace levels analysis of 33 antibiotics in water by on-line solid-phase extraction with ultra-performance liquid chromatography-tandem mass spectrometry

A method was developed for the determination of 33 antibiotics belonging to 4 different antibiotic groups, including sulfonamides (16), fluoroquinolones (12), macrolides (1), and tetracyclines (4) in water samples using on-line solid-phase extraction-ultra performance liquid chromatography-electrospray ionization tandem mass spectrometry (on-line SPE-UPLC-MS/MS). The enrichment and analysis conditions were optimized for the determination of trace concentrations (nanogram per liter). Aliquots of the water samples (5 mL) were filtered through a membrane and enriched on an on-line polymeric column with hydrophilic–lipophilic balance (HLB). The analyte was eluted by the mobile phase during on-line SPE and separated on an Acquity BEH130 column, detected by tandem mass spectrometry, and quantified using an external standard method. The optimization of the analytical methods was discussed, which included optimization of pH of the sample, filtration membrane, Na2EDTA, chromatographic column, formic acid and aqueous ammonia in mobile phase. The detection limit for all test compounds by this method was in the range of 0.2–1.5 ng/L, with recoveries of 76.6–118%. The precision of the method, as indicated by the relative standard deviation, was 2.4–7.9%. Results of analysis of surface water samples demonstrated the ability of the proposed method to analyze ultra-trace levels of antibiotics, without the need for complex manual pretreatment.

Vehicle Underway Mobile Monitoring of Volatile Organic Compounds Using Online Mass Spectrometry: Application in an Industrial Park

The environmental problem of volatile organic compounds (VOCs) pollution in industrial parks is becoming increasingly serious. Rapid and large-scale monitoring of the overall pollution in the area and identification of pollution sources are keys to efficient pollution control. However, traditional detection methods cannot achieve rapid detection, let alone accurately pinpoint the source of pollution. In this study, an online VOC mobile monitoring system based on time-of-flight mass spectrometry was used to monitor an industrial park and successfully obtain the VOC distribution image of the industrial park. Two polluted areas (A and B) were pinpointed by examining the image, and the ΣVOCs concentration ranges were 74–421 μg/m3 and 51–577 μg/m3. Eight abnormal sites with concentration peaks exceeding the standard were found, and the pollution source of one abnormal site was analyzed. The correlation between the pollution source factor of the abnormal site and the emission enterprise was as high as 0.91, and the pollution source of the abnormal site was identified. To explore whether it was affected by other surrounding enterprises, a positive matrix factorization model was further used to analyze the receptor data of abnormal site. Three pollution sources were analyzed and compared with enterprise emission sources. Combined with the location of the abnormal site and emission sources, we found that the abnormal sites were not only affected by the emission sources of surrounding enterprises but also by the emission sources of enterprises in the northeast. This approach offers rapid and large-scale monitoring of the overall pollution in an area and quickly pinpointed the location of the pollution sources. This method solves the shortcomings of traditional methods that cannot identify the location of pollution source and provides an effective technical means for the rapid detection of the pollution distribution in industrial parks for efficient screening of pollution sources.

Method Development and Qualification of pH-Based CEX UPLC Method for Monoclonal Antibodies

Post-translational modifications (“PTMs”) in monoclonal antibodies (mAbs) contribute to charge variant distribution, which will affect biological efficacy and safety. For the characterization of mAbs, charge variants are used as a critical quality attributes for product quality, stability consistency and effectiveness. Charge variants in mAbs are characterized by a time-consuming and a multistep process starting from cation/anion exchange chromatography, acidic/basic fractions collection and subsequent reverse phase (RP) liquid chromatography, coupled with mass spectrometry (MS) analysis. Hence, an alternative characterization approach that would be highly selective for ion exchange chromatography-based charge variant analysis, which is compatible with on-line MS detection, is needed in the biopharma industry. Against this backdrop, multiple studies are being conducted to develop a simple straight on-line charge variant analysis method. In this regard, we apply the current study, which aims to develop a charge variant analytical method, based on volatile buffers with low ionic strength that can be used for on-line MS detection of charge variants of mAbs. This would enable the detection on “PTMs” using low ionic strength mobile phase compatible with MS. Hence, fruitful data can be obtained with a single chromatography run without any test sample preparation, eliminating the need for multiple steps of analysis, time-consuming process and multiple sample preparation steps. Thus, Charge Variant Analysis-MS technique will allow the characterization of charge-related PTMs on the intact protein stage. In this regard, this study is about development of a method having combination of chromatography and volatile mobile phase for mass spectrometry detection of mAbs being analyzed in native form. The method is qualified considering pharmacopeia guidelines because the ultimate aim is to transfer this method for Quality Control (QC) release testing of a monoclonal antibody, which is critical for batch release and the regulatory point of view. Acidic and basic variants have been separated with high resolution peak profile. Furthermore, there was no matrix interference and good separation selectivity in terms of specificity was obtained using this method. The experimental data suggested for the linearity of the method are 2.4 mg/mL to 3.6 mg/mL with % RSD below 2.0%. Additionally, Limit of Quantitation is found to be 0.15 mg/mL, which is 5% of loading amount. Consistently, the data show that the method is precise under the same operating conditions with a short time interval. Overall a simple, accurate, robust and precise pH gradient cation exchange chromatography method was developed and qualified for the characterization of a therapeutic native mAb. Additionally, this method can be used to claim a biosimilar product profile of an in-house product compare to an innovator.

Plasma-Catalytic CO2 Hydrogenation over a Pd/ZnO Catalyst: In Situ Probing of Gas-Phase and Surface Reactions

Plasma-catalytic CO2 hydrogenation is a complex chemical process combining plasma-assisted gas-phase and surface reactions. Herein, we investigated CO2 hydrogenation over Pd/ZnO and ZnO in a tubular dielectric barrier discharge (DBD) reactor at ambient pressure. Compared to the CO2 hydrogenation using Plasma Only or Plasma + ZnO, placing Pd/ZnO in the DBD almost doubled the conversion of CO2 (36.7%) and CO yield (35.5%). The reaction pathways in the plasma-enhanced catalytic hydrogenation of CO2 were investigated by in situ Fourier transform infrared (FTIR) spectroscopy using a novel integrated in situ DBD/FTIR gas cell reactor, combined with online mass spectrometry (MS) analysis, kinetic analysis, and emission spectroscopic measurements. In plasma CO2 hydrogenation over Pd/ZnO, the hydrogenation of adsorbed surface CO2 on Pd/ZnO is the dominant reaction route for the enhanced CO2 conversion, which can be ascribed to the generation of a ZnOx overlay as a result of the strong metal–support interactions (SMSI) at the Pd–ZnO interface and the presence of abundant H species at the surface of Pd/ZnO; however, this important surface reaction can be limited in the Plasma + ZnO system due to a lack of active H species present on the ZnO surface and the absence of the SMSI. Instead, CO2 splitting to CO, both in the plasma gas phase and on the surface of ZnO, is believed to make an important contribution to the conversion of CO2 in the Plasma + ZnO system.

Controlling the reaction microenvironments through an embedding strategy to strengthen the chemical looping reforming of methane based on decoupling process

Aiming at the complexity of traditional biomass gasification technology with low conversion efficiency and high tar content and realizing the directional conversion of biomass into syngas, this paper proposed a new decoupling process of biomass pyrolysis and chemical looping reforming of volatile components. Designing a high activity and selective oxygen carrier is the key to the chemical looping reforming process. This study used an embedding strategy to develop the oxygen carrier. NiFe2O4 was embedded in SBA-15 to control the reaction microenvironment. The reaction performance of NiFe2O4@SBA-15 under different conditions was investigated via a combination of fixed-bed reactor and on-line mass spectrometry. The results showed that the CO selectivity was close to 100%. The CH4 conversion and CO selectivity of NiFe2O4@SBA-15 were increased by 121.29% and 114.40% than NiFe2O4, respectively. The optimal embedding ratio (20%) and reaction temperature (900 °C) were determined during the experiment, which was consistent with the thermodynamic simulation results. The gas–solid reaction model was used to solve the reaction kinetics of the oxygen carrier, and the activation energy was 118.23 kJ·mol−1. This study gives a research basis for screening oxygen carrier and the design of reactor in the directional conversion of biomass pyrolysis full volatiles into syngas via chemical looping reforming.

Exposure assessment of polycyclic aromatic hydrocarbons in refined coal tar sealant applications.

Refined coal tar sealant (RCTS) emulsions are used to seal the surface of asphalt pavement. Nine of the 22 polycyclic aromatic hydrocarbons (PAHs) evaluated in this study are classified as known, probable, or possible human carcinogens. Exposure assessment research for RCTS workers has not been published previously. The overall objective of this study was to develop a representative occupational exposure assessment of PAH exposure for RCTS workers based on worksite surveys. The specific aims were to: 1) quantify full-shift airborne occupational exposures to PAHs among RCTS workers; 2) quantify workers' dermal exposures to PAHs; 3) quantify biomarkers of PAH exposure in workers' urine; 4) identify specific job titles associated with RCTS exposure; and 5) apply these results to a biological exposure index to assess risk of potential genotoxicity from occupational exposures. A total of twenty-one RCTS workers were recruited from three companies. Personal and area air samples were collected using a modification of NIOSH Method 5515. Dermal exposure was assessed by hand and neck wipes before and after shifts. Twenty-two PAHs were quantified via gas chromatography-mass spectrometry selected ion monitoring. Internal dose was estimated by quantifying select PAH metabolites in pre- and post-shift urine samples using on-line solid phase extraction-high performance liquid chromatography-tandem mass spectrometry. PAH levels in the worker breathing zones were highest for naphthalene, acenaphthene, and phenanthrene, with geometric means of 52.1, 11.4, and 9.8μg/m3, respectively. Hand wipe levels of phenanthrene, fluoranthene and pyrene were the highest among the 22 PAHs with geometric means of 7.9, 7.7, and 5.5μg/cm2, respectively. Urinary PAH biomarkers for naphthalene, fluorene, phenanthrene, and pyrene were detected in all workers and were higher for post-shift samples than those collected pre-shift. Urinary concentrations of the metabolite 1-hydroxypyrene were greater than the American Conference of Governmental Industrial Hygienists (ACGIH) Biological Exposure Index (BEI) for this metabolite in 89 percent of post-shift samples collected on the final day of the work week or field survey. Statistically significances were found between concentrations of fluorene, naphthalene, and phenanthrene in the breathing zone of workers and their corresponding urinary PAH biomarkers. Workers were placed in two work place exposure groups: applicators and non-applicators. Applicators had higher total PAH concentrations in personal breathing zone (PBZ) air samples than non-applicators and were more likely to have post-shift hand wipe concentrations significantly higher than pre-shift concentrations. Concentrations of post-shift urinary biomarkers were higher, albeit not significantly, for applicators than non-applicators. The exposure results from RCTS worker samples cannot be explained by proximal factors such as nearby restaurants or construction. Air and skin concentration levels were substantially higher for RCTS workers than previously published levels among asphalt workers for all PAHs. PAH profiles on skin wipes were more consistent with RCTS sealant product than air samples. Last day post-shift urinary concentrations of 1-hydroxypyrene greatly exceeded the ACGIH BEI benchmark of 2.5μg/L in 25 of 26 samples, which suggests occupational exposure and risk of genotoxicity. When pyrene and benzo[a]pyrene were both detected, concentration ratios from personal exposure samples were used to calculate the adjusted BEI. Concentrations of 1-hydroxypyrene exceeded the adjusted BEIs for air, hand wipes, and neck wipes in most cases. These results indicate the need to increase safety controls and exposure mitigation for RCTS workers.

Elucidating the Implications of Morphology on Fundamental Characteristics of Nickel-Rich NCMs: Cracking, Gassing, Rate Capability, and Thermal Stability of Poly- and Single-Crystalline NCM622

Nickel-rich NCM (LiMO2, with M = Ni, Co, and Mn) cathode active materials for lithium-ion batteries are being increasingly commercialized due to their high specific capacity. Since the particle cracking of conventional polycrystalline NCMs is reported to be a major failure mechanism, the demand for single-crystalline materials is rising, as they are believed to provide superior cycle life. To gain comprehensive insights into the implications of NCM particle morphology on the electrochemical performance, the fundamental properties of these two material classes will be examined in this study. Krypton physisorption experiments and capacitance measurements reveal considerable differences in the change of the NCM surface area upon compression, delithiation, and charge/discharge cycling, depending on the material’s morphology. Here, a polycrystalline NCM622 exhibits changes of its specific surface area of up to 650 % when cycled to a high state of charge, while the one of a single-crystalline NCM622 remains essentially unaffected. Consequently, the difference in morphology and, therefore, in exposed NCM surface area leads to differences in the extent of gassing at high degrees of delithiation (determined via on-line electrochemical mass spectrometry), in the rate capability (evaluated in half-cell discharge rate tests), and in the thermal stability (assessed by thermogravimetric analysis).

Accurate Identification of Pollution Sources in a Chemical Enterprise Based on a Distributed Multi-channel VOCs Online Monitoring Mass Spectrometry System

A monitoring and traceability management system for unorganized emissions of volatile organic compounds (VOCs) in industrial parks has been established. This system uses distributed multi-channel mass spectrometry to continuously monitor multiple online monitoring points within the enterprise and the factory boundary to initially identify the source of unorganized emissions of VOCs. Based on online monitoring data, the system combined a positive matrix factorization (PMF) model and conditional bivariate probability function (CBPF) methods to accurately identify pollution sources of different scales in the park. The system was successfully applied to a pharmaceutical chemical factory in Taizhou Chemical Industry Park, and VOCs online monitoring was carried out for more than three months at 10 monitoring sites in the factory area. The sources of VOCs were analyzed using the PMF model, and the geographical location information of each pollution source factor was identified by the CBPF method. During the monitoring period, the contribution of chlorobenzene emissions and the number of early warnings were much higher than those of other species. Compared with that of other species, the frequency of abnormal emissions of butene was higher, and the frequency of abnormal emissions of toluene was lower. Among the top ten species, only chlorobenzene had significant concentration changes in different monitoring sites. Ambient VOCs in the plant mainly came from six sources:butene emission, toluene emission, chlorobenzene emission, solvent use, sulfur-related processes, and industrial production. Based on the CBPF results of each pollution source factor relative to the ten monitoring stations, the local pollution source and external pollution source in the plant were distinguished, and the specific location of the local pollution source and the transmission direction of the external pollution source were identified.

Scalable fabrication of antimony nanoparticles confined in a porous carbon framework for high-performance sodium-ion batteries

Engineering of carbon/metal nanocomposites with small metal particles is promising for the development of alloy-type anodes. Herein, an [email protected] composite was developed from a commercial potassium antimony tartrate precursor using a scalable pyrolysis method. Ultrafine Sb nanoparticles are confined within a porous carbon framework, which substantially facilitates the diffusion of Na-ion/electrons and effectively alleviates the charging/discharging induced volume change. The obtained [email protected] material displays excellent electrochemical performance for Na+ storage. The Na+ diffusion behavior of [email protected] was comprehensively investigated using various methods, and its gas evolution during the discharge/charge was monitored via online mass spectrometry. Then, [email protected] was assembled into full cells. During discharge/charge processes, the Na3V2(PO4)2F3/[email protected] full cells delivered a competitive working voltage of 2.95 V and a capacity retention of 93.4% (50 cycles @ 0.2 A g−1). Considering its facile preparation method from a commercial precursor, the [email protected] composite can potentially realize a large-scale application of sodium-ion batteries.

Selective electrocatalytic reduction of nitrate to dinitrogen by Cu2O nanowires with mixed oxidation-state

• CuO/Cu 2 O NWs contains switchable oxidation states of Cu (I/II to 0/I). • N 2 selectivity is 99.8% over Cu/Cu 2 O NWs, the highest reported so far. • Cu/Cu 2 O NWs provides active sites for hydrogen/oxygen-adsorbing simultaneously. • Cu/Cu 2 O NWs yields sufficient H* and limit hydrogen bubbles negative effect. • N 2 production based on NO 3 RR is proceeded by H*-mediated route. Selective electrocatalytic nitrate reduction reaction to dinitrogen is a promising water treatment technology to manage nitrate. While, a lack of efficient electrode remains the primary hurdle for achieving the goal. For non-noble electrode, the strong adsorption of oxygen atoms on Cu resulted in low selectivity and inducing nitrite accumulation during the long-term operation. Herein, it is found that Cu 2 O nanowires with mixed oxidation-state can selective reduction of nitrate to dinitrogen. CuO-coated Cu 2 O nanowires (CuO/Cu 2 O NWs) was electrochemically converted into Cu/Cu 2 O NWs for hydrogen/oxygen-adsorbing which was verified by In-situ infrared spectro-electrochemical experiments. H 2 split and H*-adsorbing of Cu/Cu 2 O are desired to yield sufficient H* and limit hydrogen bubbles negative effect. Online differential electrochemical mass spectrometry confirmed dinitrogen generation over Cu/Cu 2 O NWs with over 99.8% selectivity. Computational studies suggest that active Cu/Cu 2 O NWs reduces the free energy changes associated with both nitrate activation and N − N coupling. Energetically favorable pathways for dinitrogen production based on nitrate reduction are proposed herein and the origin of this selective dinitrogen formation is clarified.

A Rapid LC-MS/MS-PRM Assay for Serologic Quantification of Sialylated O-HPX Glycoforms in Patients with Liver Fibrosis.

Development of high throughput robust methods is a prerequisite for a successful clinical use of LC-MS/MS assays. In earlier studies, we reported that nLC-MS/MS measurement of the O-glycoforms of HPX is an indicator of liver fibrosis. In this study, we show that a microflow LC-MS/MS method using a single column setup for capture of the analytes, desalting, fast gradient elution, and on-line mass spectrometry measurements, is robust, substantially faster, and even more sensitive than our nLC setup. We demonstrate applicability of the workflow on the quantification of the O-HPX glycoforms in unfractionated serum samples of control and liver disease patients. The assay requires microliter volumes of serum samples, and the platform is amenable to one hundred sample injections per day, providing a valuable tool for biomarker validation and screening studies.

Rapid Evaluation of the Extent of Haptoglobin Glycosylation Using Orthogonal Intact-Mass MS Approaches and Multivariate Analysis.

Intact-mass measurements are becoming increasingly popular in mass spectrometry (MS) based protein characterization, as they allow the entire complement of proteoforms to be evaluated within a relatively short time. However, applications of this approach are currently limited to systems exhibiting relatively modest degrees of structural diversity, as the high extent of heterogeneity frequently prevents straightforward MS measurements. Incorporation of limited charge reduction into electrospray ionization (ESI) MS is an elegant way to obtain meaningful information on most heterogeneous systems, yielding not only the average mass of the protein but also the mass range populated by the entire complement of proteoforms. Application of this approach to characterization of two different phenotypes of haptoglobin (1-1 and 2-1) provides evidence of a significant difference in their extent of glycosylation (with the glycan load of phenotype 2-1 being notably lighter) despite a significant overlap of their ionic signals. More detailed characterization of their glycosylation patterns is enabled by the recently introduced technique of cross-path reactive chromatography (XP-RC) with online MS detection, which combines chromatographic separation with in-line reduction of disulfide bonds to generate metastable haptoglobin subunits. Application of XP-RC to both haptoglobin phenotypes confirms that no modifications are present within their light chains and provides a wealth of information on glycosylation patterns of the heavy chains. N-Glycosylation patterns of both haptoglobin phenotypes were found to be consistent with bi- and triantennary structures of complex type that exhibit significant level of fucosylation and sialylation. However, multivariate analysis of haptoglobin 1-1 reveals higher number of the triantennary structures, in comparison to haptoglobin 2-1, as well as a higher extent of fucosylation. The glycosylation patterns deduced from the XP-RC/MS measurements are in agreement with the conclusions of the intact-mass analysis supplemented by limited charge reduction, suggesting that the latter technique can be employed in situations when fast assessment of protein heterogeneity is needed (e.g., process analytical technology applications).

Experimental and kinetic study on flash pyrolysis of biomass via on-line photoionization mass spectrometry

Experimental and kinetic study on flash pyrolysis of solid fuels is a challenge since its process usually occurs in a very few seconds. To do this successfully, a perfect combination of high heating rates, plug flow reactor, on-line sampling, real-time analysis and fast acquisition (e.g., < 300 ms/spectrum) is indispensable. In this work, a microfluidized-bed reactor (MFBR) was connected to the single photoionization time-of-flight mass spectrometer (SPI-TOFMS) to explore the kinetic process from flash pyrolysis of cellulose. The hydrodynamics of MFBR at different pyrolysis temperatures and with three model compounds were analyzed. The time-evolved profiles of primary tar from flash pyrolysis were recorded by SPI-TOFMS. The effect of experimental conditions (including pyrolysis temperature, transfer-line temperature and the type of carrier gas) on the kinetics of flash pyrolysis was systematically discussed. Besides, experimental measurements were also compared with kinetic modeling results, which shows a much better agreement between them than previous work. The obtained results prove that the MFBR combined with SPI-TOFMS is a potential and reliable method to experimentally study the flash pyrolysis of solid fuels.

Activating Surface Lattice Oxygen of a Cu/Zn1-xCuxO Catalyst through Interface Interactions for CO Oxidation.

Surface lattice oxygen in metal oxides is a common participant in many chemical reactions. Given this, the structural design of catalysts to activate lattice oxygen and moreover investigations into the effect of lattice oxygen on reaction pathways are hot topics. With this in mind, herein we prepare CuO-Zn1-xCuxO (ZCO) nanofibers akin to the Trojan horse legend and via an in situ reduction obtain activated Cu/Zn1-xCuxO (Cu/ZCO) nanofibers. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy reveal that surface lattice oxygen of Cu/ZCO is effectively activated from inert O2- to reactive O2-x. This activation stems from the enhanced covalence of metal-oxygen bonds and the electron transfer between Cu and the support. Online mass spectrometry reveals that Cu/ZCO with activated lattice oxygen exhibits a higher Mars-van Krevelen reaction efficiency during the CO oxidation process. This study offers a new avenue to engineer interface interactions, given, as highlighted here, the importance of surface lattice oxygen in oxide supports during the catalytic process.

Metal-organic framework derived carbon-supported bimetallic copper-nickel alloy electrocatalysts for highly selective nitrate reduction to ammonia

Developing electrocatalysts for efficient reduction of nitrate contaminant to value-added ammonia as energy carrier is a pivotal part for restoring the nitrogen cycle. However, the selectivity of ammonia is far from satisfaction, often suffering from accumulation of toxic nitrite byproduct. Herein, a series of CuNi alloy nanoparticles embedded in nitrogen-doped carbon matrix (CuNi/NC) with hierarchical pores were fabricated by pyrolysis of bimetallic metal–organic frameworks (MOFs). The catalysts exhibited excellent selectivity (94.4%) and faradaic efficiency (79.6%) for nitrate reduction to ammonia, greatly outperforming the performance of monometallic Cu/NC (selectivity of 60.8% and faradaic efficiency of 60.6%). Impressively, the introduction of nickel distinctly suppressed the production of toxic byproduct of nitrite. Online differential electrochemical mass spectrometry (DEMS) and in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) tests were utilized to reveal the key intermediates and the reaction pathway. Density functional theory (DFT) calculations demonstrated that the introducing of nickel into copper lattice modified both the electronic and geometric structures of the catalysts. The copper and nickel sites in the CuNi alloy catalysts operate synergistically to facilitate the hydrogenation of NO2* to HNO2* and suppress the hydrogen evolution reaction, boosting the selective formation of ammonia. This work could provide a new synthetic route for bimetallic catalysts and mechanistic understanding for nitrate to ammonia reaction.

Insight into the Activity and Selectivity of Nanostructured Copper Titanates during Electrochemical Conversion of CO2 at Neutral pH via In Situ X-ray Absorption Spectroscopy.

The electrochemical conversion of carbon dioxide (CO2) to useful chemical fuels is a promising route toward the achievement of carbon neutral and carbon negative energy technologies. Copper (Cu)- and Cu oxide-derived surfaces are known to electrochemically convert CO2 to high-value and energy-dense products. However, the nature and stability of oxidized Cu species under reaction conditions are the subject of much debate in the literature. Herein, we present the synthesis and characterization of copper-titanate nanocatalysts, with discrete Cu-O coordination environments, for the electrochemical CO2 reduction reaction (CO2RR). We employ real-time in situ X-ray absorption spectroscopy (XAS) to monitor Cu species under neutral-pH CO2RR conditions. Combination of voltammetry and on-line electrochemical mass spectrometry with XAS results demonstrates that the titanate motif promotes the retention of oxidized Cu species under reducing conditions for extended periods, without itself possessing any CO2RR activity. Additionally, we demonstrate that the specific nature of the Cu-O environment and the size of the catalyst dictate the long-term stability of the oxidized Cu species and, subsequently, the product selectivity.

Contrasting Chemical Complexity and the Reactive Organic Carbon Budget of Indoor and Outdoor Air.

Reactive organic carbon (ROC) comprises a substantial fraction of the total atmospheric carbon budget. Emissions of ROC fuel atmospheric oxidation chemistry to produce secondary pollutants including ozone, carbon dioxide, and particulate matter. Compared to the outdoor atmosphere, the indoor organic carbon budget is comparatively understudied. We characterized indoor ROC in a test house during unoccupied, cooking, and cleaning scenarios using various online mass spectrometry and gas chromatography measurements of gaseous and particulate organics. Cooking greatly impacted indoor ROC concentrations and bulk physicochemical properties (e.g., volatility and oxidation state), while cleaning yielded relatively insubstantial changes. Additionally, cooking enhanced the reactivities of hydroxyl radicals and ozone toward indoor ROC. We observed consistently higher median ROC concentrations indoors (≥223 μg C m-3) compared to outdoors (54 μg C m-3), demonstrating that buildings can be a net source of reactive carbon to the outdoor atmosphere, following its removal by ventilation. We estimate the unoccupied test house emitted 0.7 g C day-1 from ROC to outdoors. Indoor ROC emissions may thus play an important role in air quality and secondary pollutant formation outdoors, particularly in urban and suburban areas, and indoors during the use of oxidant-generating air purifiers.