Rapid and accurate determination of trace volatile sulfur compounds in human halitosis by an adaptable active sampling system coupling with gas chromatography

Halitosis with the main components of trace volatile sulfur compounds widely affects the quality of life. In this study, an adaptable active sampling system with two sample‐collection modes of direct injection and solid‐phase microextraction was developed for the rapid and precise determination of trace volatile sulfur compounds in human halitosis coupled with gas chromatography–flame photometric detection. The active sampling system was well designed and produced for efficiently sampling and precisely determining trace volatile targets in halitosis under the optimized sampling and detection conditions. The analytical method established was successfully applied for the determination of trace targets in halitosis. The limits of detection of H₂S, CH₃SH, and CH₃SCH₃ by direct injection were 0.0140–23.0 μg/L with good recoveries ranging from 82.2 to 118% and satisfactory relative standard deviations of 0.4–9.5% (n = 3), respectively. The limit of detections of CH₃SH and CH₃SCH₃ by solid‐phase microextraction were 2.03 and 0.186 × 10^?3 μg/L with good recoveries ranging from 98.3 to 108% and relative standard deviations of 5.9–9.0% (n = 3). Trace volatile targets in positive real samples could be actually found and quantified by combination of direct injection and solid‐phase microextraction. This method was reliable and efficient for the determination of trace volatile sulfur compounds in halitosis.     

Magnetic Ti3C2Tx/Fe3O4/Ag substrate for rapid quantification of trace sulfonamides in aquatic products by surface enhanced Raman spectroscopy

Surface-enhanced Raman scattering (SERS) spectroscopy has been employed as a rapid analysis technology for food security inspection recently. Nowadays, it is still a great challenge to rapidly quantify multiple trace antibiotics potentially abused in aquaculture industry. In this work, a magnetic Ti₃C₂T_x/Fe₃O₄/Ag substrate was prepared for the development of a reliable rapid SERS quantification method for multiple trace sulfonamides in aquatic products. This magnetic substrate had good uniformity, reproducibility, stability and SERS activity. Moreover, this substrate could integrate the magnetic separation-enrichment and matrix clean-up without cross contamination, which endowed it with good selectivity and anti-interference capability during real sample analysis. The electromagnetic enhancement and chemical enhancement mechanism of this magnetic substrate were studied in detail to reveal its good separation-enrichment performance and SERS activity. Finally, a rapid SERS quantification method was established and practically applied for trace phthalic sulfathiazole (PST) and silver sulfadiazine (SSD) in aquatic products by using Ti₃C₂T_x/Fe₃O₄/Ag magnetic substrates. Trace PST and SSD could be actually detected and quantified as 55.9 µg/kg and 64.0 µg/kg in aquatic products, respectively. Good recoveries of 83.9%–116% with relative standard deviations (RSDs) of 0.5%–3.2% for PST and 80.2%–102% with RSDs of 1.3%–5.8% for SSD were obtained. This work proposed an efficient and reliable method for rapid quantification of trace multiple sulfonamides in complex aquatic samples during food security inspection.     

Extraction and preconcentration of formaldehyde in water by polypyrrole‐coated magnetic nanoparticles and determination by high‐performance liquid chromatography

In this study, a simple and rapid extraction method based on the application of polypyrrole‐coated Fe₃O₄ nanoparticles as a magnetic solid‐phase extraction sorbent was successfully developed for the extraction and preconcentration of trace amounts of formaldehyde after derivatization with 2,4‐dinitrophenylhydrazine. The analyses were performed by high‐performance liquid chromatography followed by UV detection. Several variables affecting the extraction efficiency of the formaldehyde, i.e., sample pH, amount of sorbent, salt concentration, extraction time and desorption conditions were investigated and optimized. The best working conditions were as follows: sample pH, 5; amount of sorbent, 40 mg; NaCl concentration, 20% w/v; sample volume, 20 mL; extraction time, 12 min; and 100 μL of methanol for desorption of the formaldehyde within 3 min. Under the optimal conditions, the performance of the proposed method was studied in terms of linear dynamic range (10–500 μg/L), correlation coefficient (R² ≥ 0.998), precision (RSD% ≤ 5.5) and limit of detection (4 μg/L). Finally, the developed method was successfully applied for extraction and determination of formaldehyde in tap, rain and tomato water samples, and satisfactory results were obtained.     

Extraction of methocarbamol from human plasma with a polypyrrole/multiwalled carbon nanotubes composite decorated with magnetic nanoparticles as an adsorbent followed by electrospray ionization ion mobility spectrometry detection†

In this work, a polypyrrole/multiwalled carbon nanotubes composite decorated with Fe₃O₄ nanoparticles was chemically synthesized and applied as a novel adsorbent for the extraction of methocarbamol from human plasma. Electrospray ionization ion mobility spectrometry was used for the determination of the analyte. The properties of the magnetic‐modified adsorbent were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform IR spectroscopy, and X‐ray diffraction. The effects of experimental parameters on the extraction efficiency of the sorbent were investigated. Under the optimized conditions, the linear dynamic range was found to be 2–150 ng/mL with the detection limit of 0.9 ng/mL. The relative standard deviation was 5.3% for three replicate measurements of methocarbamol in plasma sample. The extraction efficiency of the sorbent for the determination of different drugs with various polarities was also compared to that of Fe₃O₄‐polypyrrole and Fe₃O₄‐multiwalled carbon nanotubes sorbents. Finally, the method was used for the determination of methocarbamol in blood samples.     

Synthesis and application of boronic acid‐functionalized magnetic adsorbent for sensitive analysis of salbutamol residues in pig tissues

Salbutamol (SAL) is the most widely used β₂‐agonist drug for asthma and chronic obstructive pulmonary patients, but it is also often abused as feed additive. In recent years, the abuse of SAL has led to a large number of food safety incidents. Therefore, the monitoring of SAL residues in animal products is very important. A highly selective boronate affinity magnetic adsorbent was synthesized and developed for detection of trace levels of SAL residues in pig tissue samples. The obtained Fe₃O₄@SiO₂@FPBA(4‐formylphenylboronic acid) magnetic adsorbent showed good adsorption ability to catechol and SAL, and then it was successfully applied as special magnetic solid‐phase phase extraction adsorbent coupled with high‐performance liquid chromatography (HPLC) for simultaneous isolation and determination of cis‐diol compounds. The binding capacity of catechol and SAL reached 96 and 50 µmol/g, respectively. The method was successfully established for the detection of trace levels of SAL in pig tissue samples. The linear range extended from 0.32 to 800 µg/kg (R² = 0.9994). The limit of detection of SAL was 0.19 µg/kg. The recoveries were satisfactory (89.5–108.0%) at three spiked levels with RSD between 2.1 and 11.3%. These results indicated that the method has potential for enrichment and detection of trace levels of SAL residual in animal food products. Copyright © 2015 John Wiley & Sons, Ltd.     

Study on the formation process of MoO3/Fe2(MoO4)3 by mechanochemical synthesis and their catalytic performance in methanol to formaldehyde

Mechanochemical method has applied to the green preparation of iron-molybdenum catalyst efficiently, and their catalytic performance was evaluated by the oxidation of methanol to formaldehyde. In order to investigate the formation process of iron-molybdenum catalyst based on mechanochemical method, various characterization techniques have been employed. Results indicate that iron-molybdenum catalyst could not be generated during ball milling process without calcining, and calcination is crucial step to regulate the ratio of MoO₃ and Fe₂(MoO₄)₃. For the formation of MoO₃ and Fe₂(MoO₄)₃ phase, 180 °C could be the key turning temperature point. Fe₂(MoO₄)₃ and MoO₃ phases are concurrently emerged when Mo/Fe atomic ratio exceeds 1.5. The aggregation of Fe₂(MoO₄)₃ is severe with the increasing calcination temperature. Fe₂(MoO₄)₃ is stable below 600 °C, while MoO₃ phase could be subliming with the increasing temperature. The catalytic performance of iron-molybdenum catalyst has closely correlation with the phase compositions, which can be controlled by synthesis temperature and Mo/Fe molar ratio. The iron-molybdenum catalyst with Mo/Fe atomic ratio of 2.6 calcined at 500 °C for 4 h showed the best methanol conversion (100%) and formaldehyde yield (92.27%).

     

Poypyrrole/molybdenum trioxide/graphene nanoribbon ternary nanocomposite with enhanced capacitive performance as an electrode for supercapacitor

A polypyrrole/molybdenum trioxide/graphene nanoribbon (PPy/MoO₃/GNR) ternary nanocomposite was successfully synthesized via an in situ method. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses show that MoO₃ was successfully combined with the GNRs. The one-dimensional morphology was observed using field emission scanning electron microscopy and transmission electron microscopy. The electrochemical tests show that the PPy/MoO₃/GNR ternary nanocomposite exhibits the highest specific capacitance (844 F g^?1) among the investigated materials and exhibits good cycling stability for 1000 cycles. These results collectively demonstrate that the combination of each component can efficiently increase the specific capacitance and cycling stability. As such, the method reported herein represents a promising approach for fabricating supercapacitor electrode materials.     

Enhanced sulfur‐resistant methanation performance over MoO3–ZrO2 catalyst prepared by solution combustion method

Sulfur‐resistant methanation of syngas was studied over MoO₃–ZrO₂ catalysts at 400°C. The MoO₃–ZrO₂ solid‐solution catalysts were prepared using the solution combustion method by varying MoO₃ content and temperature. The 15MoO₃–ZrO₂ catalyst achieved the highest methanation performance with CO conversion up to 80% at 400°C. The structure of ZrO₂ and dispersed MoO₃ species was characterized using X‐ray diffraction and transmission electron microscopy. The energy‐dispersive spectrum of the 15MoO₃–ZrO₂ catalyst showed that the solution combustion method gave well‐dispersed MoO₃ particles on the surface of ZrO₂. The structure of the catalysts depends on the Mo surface density. It was observed that in the 15MoO₃–ZrO₂ catalyst the Mo surface density of 4.2 Mo atoms nm^?2 approaches the theoretical monolayer capacity of 5 Mo atoms nm^?2. The addition of a small amount of MoO₃ to ZrO₂ led to higher tetragonal content of ZrO₂ along with a reduction of particle size. This leads to an efficient catalyst for the low‐temperature CO methanation process.     

Electrochemistry of MoO3–K2MoO4 melts: a chance to control the nature of reduced molybdenum oxides

Cathodic electrodeposition of oxides on platinum from MoO₃–K₂MoO₄ (3.85–75?mol% MoO₃) under DC and pulsed galvanostatic modes is discussed in combination with voltammetry data. Characteristic potential values (as related to oxygen evolution onset) are reported for Mo(VI/IV) redox processes, as well as for electrochemical equilibria with participation of molybdenum metal and Pt–Mo alloys. On the basis of scan rate effects and results for various potential limits, and also of voltammetry with preliminary potentiostatic accumulation of products, molybdate reduction mechanism complicated by a chemical step of Mo metal oxidation is proposed. This qualitative assumption is verified in preparative electrolysis experiments with products identification by means of X-ray diffractometry, scanning electron microscopy, and EDX local analysis. Deposition under pulsed mode is found to be useful tool to adjust the duration of chemical step and by these means to alter the composition of final products. The conditions supporting the formation of MoO₂ and more reduced oxides are formulated.     

Synthesis and application of a novel solid‐phase extraction adsorbent for multiresidue analysis of insecticides in water

A new solid‐phase adsorbent was synthesized for the simultaneous enrichment of multiple classes of trace insecticides (neonicotinoids, organophosphates, fiproles, and organochlorines) in water. The adsorbent was spherical with a diameter, surface area, average pore volume, and pore size of approximately 5 μm, 341 m²/g, 0.092 m³/g, and 2.22 nm, respectively. Extraction conditions were optimized, including water pH and the type and volume of the rinsing and eluting solvents. After extraction, target insecticides were analyzed by gas chromatography with mass spectrometry and high‐performance liquid chromatography with tandem mass spectrometry. The recovery of neonicotinoids ranged from 63.0 to 124%, except for clothianidin (40.1–52.9%). Recoveries of organophosphates, fiproles, and organochlorines were in the ranges of 37.0–102, 64.0–101, and 42.0–69.3%, respectively. Relative standard deviations were <20% except for profenofos (5.1–30%) and method detection limits were 1.8–12.7 ng/L, suggesting that the precision and accuracy of the developed method were viable. At environmentally relevant concentrations, the new adsorbent achieved comparable recoveries of target insecticides to hydrophilic–lipophilic balance adsorbent while providing an additional advantage by further reducing matrix effects. Field water samples from the Pearl River in Guangzhou, China were analyzed, and the frequent detection of neonicotinoids raises concerns about their aquatic risk.     

Preparation of iron‐based MIL‐101 functionalized polydopamine@Fe3O4 magnetic composites for extracting sulfonylurea herbicides from environmental water and vegetable samples

Here, we describe a simple one‐pot solvothermal method for synthesizing MIL‐101(Fe)@polydopamine@Fe₃O₄ composites from polydopamine‐modified Fe₃O₄ particles. The composite was used as a magnetic adsorbent to rapidly extract sulfonylurea herbicides. The herbicides were then analyzed by high‐performance liquid chromatography. The best possible extraction efficiencies were achieved by optimizing the most important extraction parameters, including desorption conditions, extraction time, adsorbent dose, salt concentration, and the pH of the solution. Good linearity was found (correlation coefficients >0.9991) over the herbicide concentration range 1–150 μg/L using the optimal conditions. The limits of detection (the concentrations giving signal/noise ratios of 3) were low, at 0.12–0.34 μg/L, and repeatability was good (the relative standard deviations were <4.8%, n = 6). The method was used successfully to determine four sulfonylurea herbicides in environmental water and vegetable samples, giving satisfactory recoveries of 87.1–108.9%. The extraction efficiency achieved using MIL‐101(Fe)@polydopamine@Fe₃O₄ was compared with the extraction efficiencies achieved using other magnetic composites (polydopamine@Fe₃O₄, Hong Kong University of Science and Technology (HKUST)‐1@polydopamine@Fe₃O₄, and MIL‐100(Fe)@polydopamine@Fe₃O₄). The results showed that the magnetic MIL‐101(Fe)@polydopamine@Fe₃O₄ composites have great potential for the extraction of trace sulfonylurea herbicides from various sample types.     

Dispersed platinum supported by hydrogen molybdenum bronze-modified carbon as electrocatalyst for methanol oxidation

A new electrocatalyst, Pt/H_xMoO₃-C, for methanol oxidation, was prepared by dispersing platinum nano-particles on Vulcan XC-72 modified by hydrogen molybdenum bronze (H_xMoO₃, 0 ≤ x ≤ 2). The modification of Vulcan XC-72 with H_xMoO₃ on was accomplished by reducing the adsorbed molybdic acid and the platinum nano-particles were dispersed on the modified carbon by reducing chloroplatinic acid, with formaldehyde as the reductant. The prepared Pt/H_xMoO₃-C was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersion spectrometer, cyclic voltammetry (CV), chronoamperometry (CA), and single-cell test, with a comparison of the electrocatalyst, carbon-supported platinum (Pt/C) prepared under the same condition but without the modification. The results obtained from XRD and SEM showed that the modification of Vulcan XC-72 with H_xMoO₃ reduced the platinum particle size and improved distribution uniformity of platinum on carbon. The results, obtained from CV, CA, and the single-cell test, showed that Pt/H_xMoO₃-C exhibited better electrocatalytic activity toward methanol oxidation than Pt/C.     

Polypyrrole‐magnetite dispersive micro‐solid‐phase extraction combined with ultraviolet‐visible spectrophotometry for the determination of rhodamine 6G and crystal violet in textile wastewater

Polypyrrole‐magnetite dispersive micro‐solid‐phase extraction method combined with ultraviolet‐visible spectrophotometry was developed for the determination of selected cationic dyes in textile wastewater. Polypyrrole‐magnetite was used as adsorbent due to its thermal stability, magnetic properties, and ability to adsorb Rhodamine 6G and crystal violet. Dispersive micro‐solid‐phase extraction parameters were optimized, including sample pH, adsorbent amount, extraction time, and desorption solvent. The optimum polypyrrole‐magnetite dispersive micro‐solid phase‐extraction conditions were sample pH 8, 60 mg polypyrrole‐magnetite adsorbent, 5 min of extraction time, and acetonitrile as the desorption solvent. Under the optimized conditions, the polypyrrole‐magnetite dispersive micro‐solid‐phase extraction with ultraviolet‐visible method showed good linearity in the range of 0.05–7 mg/L (R ² > 0.9980). The method also showed a good limit of detection for the dyes (0.05 mg/L) and good analyte recoveries (97.4–111.3%) with relative standard deviations < 10%. The method was successfully applied to the analysis of dyes in textile wastewater samples where the concentration found was 1.03 mg (RSD ±7.9%) and 1.13 mg/L (RSD ± 4.6%) for Rhodamine 6G and crystal violet, respectively. It can be concluded that this method can be adopted for the rapid extraction and determination of dyes at trace concentration levels.     

Ultrasound‐assisted magnetic SPE based on Fe3O4‐grafted graphene for the determination of polychlorinated biphenyls in water samples

An ultrasound‐assisted magnetic SPE procedure with an Fe₃O₄‐grafted graphene nanocomposite as the magnetic adsorbent has been developed to determine seven polychlorinated biphenyls (PCBs; PCB28, PCB52, PCB101, PCB118, PCB138, PCB153, and PCB180) simultaneously in 200 mL environmental water samples, in combination with GC–MS/MS. Several factors related to magnetic SPE efficiencies, such as the superparamagnetic intensity and amount of adsorbent, extraction time, sample pH, and desorption conditions were investigated. With the assistance of ultrasound, the extraction achieved the maximum within only 20 s, attributed to the powerful adsorptive ability of the magnetic adsorbent toward the PCBs. Under the optimized conditions, an excellent linearity was observed in the range of 0.1–100 ng/L for PCB28, 0.2–100 ng/L for PCB52, and 0.5–100 ng/L for the other five PCBs with the correlation coefficients ranging from 0.9988 to 0.9996. The mean recoveries at spiked levels of 5.0 and 10.0 ng/L were 84.9–108.5%, the coefficients of variations were <6.5%. With convenient magnetic separation, the synthesized magnetic adsorbent could be recycled more than ten times. The proposed method was demonstrated to be feasible, simple, rapid, and easy to operate for the trace analysis of the PCBs in environmental water samples.     

具有优异甲醇催化氧化性能的Pt/MoO3-WO3/CNTs催化剂

以聚二烯丙基二甲基胺盐酸盐(PDDA)为连接剂,采用原位自组装方式将MoO3和WO3负载到碳纳米管(CNTs)上,然后通过乙二醇还原法负载Pt纳米颗粒,得到Pt纳米颗粒均匀分布的Pt/MoO3-WO3/CNTs催化剂.当氧化物总量控制在10 wt%,MoO3与WO3摩尔比为1:0.5时,Pt/MoO3-WO3/CNTs催化剂催化甲醇氧化活性最高,甲醇氧化峰电流If高达835 A/gPt.WO3和MoO3的加入提高了催化剂的甲醇氧化活性、抗CO中毒能力和稳定性,使得Pt/MoO3-WO3/CNTs催化剂表现出优异的甲醇电催化氧化性能.     

Kinetic tendencies of thermal transformations in nanosized Ni–MoO3 systems

The transformations in nanosized Ni–MoO₃ systems were studied by optical spectroscopy, microscopy, and gravimetry depending on the thickness of the Ni (d = 1–40 nm) and MoO₃ (d = 3–50 nm) films, temperature (473–773 K), and thermal treatment time. The contact potential difference was measured for Ni and MoO3 films; photovoltage, for Ni–MoO₃ systems. An energy band diagram of the Ni–MoO₃ systems was constructed. A model of the thermal transformation of MoO₃ films in Ni–MoO₃ systems was suggested, which involves a redistribution of equilibrium charge carriers at the contact, formation of a [(V_а)⁺⁺е] center during the preparation of the MoO₃ film, the transformation of this center into an [е(V_а)⁺⁺е] center during the formation of Ni–MoO₃ systems, and the thermal transition of an electron to the level of the [(V_а)⁺⁺е] center to form an [е(V_а)⁺⁺е] center.

     

The Semiquantitative Determination of Impurities in High-Purity Molybdenum Metal by Optical Emission Spectrography

Abstract

A method is reported for the determination of Ni, Co, Bi, Al, V, Ti, Cu, Si, Pb, Cr, Mg, Sn, and Fe in molybdenum metal by optical emission spectrography. The procedure consists of dissolving the metal in HNO₃ and HCl, evaporating to dryness, and igniting at 500–550°C to MoO₃. The MoO₃ is mixed with an equal weight of GeO₂, which acts as an inert collector, and ignited at 700–750°C to volatilize the MoO₃. This double ignition method concentrates the impurities on the GeO₂ thereby placing the trace elements within the range of the spectrograph. The residue is excited in a d c are at 10 amps and the spectra are recorded on a photographic emulsion.     

Monitoring of N-doped organic xerogels pyrolysis by TG–MS

Pyrolysis of N-doped organic xerogels prepared from different N-containing precursors has been studied by TG–MS. The pyrolytic process has been ascertained to consist of three steps. The first step (up to cca. 250 °C) has been interpreted as water loss (humidity, fixed water from pores) and in some cases as formaldehyde loss. The second step has been connected with volatile substances evolution (cca. 250–450 °C) with predominant release of NH₃, CO₂ and products of melamine (M) or urea decomposition. Reaction/pore water and formaldehyde have also been detected in this step. The third step of pyrolysis (450–1,000 °C) has been ascribed to carbonization reaction when the other releases of NH₃, CO₂, reaction/pore water and M decomposition products have continued. This was accompanied with evolution of H₂ and 3-hydroxypyridine. On the basis of TG measurements, it was found that increasing time of condensation of organic xerogels and amount of used catalyst lead to higher yield of carbonaceous products. In addition, adsorption experiments of Pb(II) on N-doped carbon xerogels proved that relationship between adsorption properties of xerogels and nitrogen loss during pyrolysis exists. When the sample contains only amino groups, they are lost during pyrolysis as ammonia and the adsorption ability is low, while nitrogen comprised in the aromatic rings of N-precursors stays in the structure and causes enlarging of adsorption capacity.     

Cluster‐Based Self‐Assembly Route toward MoO3 Single‐Walled Nanotubes

MoO₃ has a unique rigid double‐layer structure, which makes it a real challenge to prepare nanotubular structures. The controlled synthesis of MoO₃ single‐walled nanotubes (SWNTs) is achieved through a cluster‐based self‐assembly route on the dodecanethiol/water interface. Various factors are studied at length, including precursor type, reaction time, temperature, pH value, and their influence on the morphology of products. The concept of “self‐assembly—from simple clusters to nanostructures” is proposed here based on preliminary results from the synthesis of MoO₃ SWNTs, which provides a new aspect for traditional synthetic chemistry of nanomaterials and polyoxometalates.     

Recovery of MoO3 from spent catalysts of partial oxidation of methanol to formaldehyde

An effect of an ammonia solution concentration, temperature, l: s ratio on a MoO₃ extraction process was revealed in studying ammonia leaching of molybdenum oxide from spent iron-molybdenum catalyst of oxidation of methanol to formaldehyde The data obtained allow to optimize the extraction process of MoO₃ from the spent Fe-Mo catalysts.