Ppm Concentration Level Research Articles

Portable automated handheld sample collection-preparation instrument for airborne volatile substances

The development of the instrument which will significantly ease the in situ samplings of volatile compounds is described. The purpose of this work was to design an automated, portable, handheld sample collection device that operates with monolithic adsorbents. The sampler contains two lithium-ion batteries, collects samples into micro-liter range volume vials, is supplied with a changeable 100 µm inner diameter six cm long capillary with an in-tube monolithic solid-phase micro-extraction adsorbent. Modeling experiments with triethylamine and diethylamine demonstrated that instrument captured samples containing volatile substances in the range of 3.5 to 118 ppm concentration levels in the air. The substances have been analyzed using a dedicated capillary electrophoresis contactless conductivity detection system and determined amounts of volatile substances in the sample solutions ranged between 3.4 and 1010 µM. Only 0.44 mL of air was enough to adsorb substances on the adsorbent, collecting them into 50 µL of water and achieving a preconcentration effect. The developed instrument is expected to find it’s applications where sampled air or gas volume is in µL – mL range: (a) collection of volatile substances near single plant parts in vivo, (b) collection of beetle pheromones in vivo, (c) volume-restricted machinery and other related applications.

Surface Modification of Magnetic Nanoparticles by Carbon-Coating Can Increase Its Biosafety: Evidences from Biochemical and Neurobehavioral Tests in Zebrafish.

Recently, magnetic nanoparticles (MNPs) have gained much attention in the field of biomedical engineering for therapeutic as well as diagnostic purposes. Carbon magnetic nanoparticles (C-MNPs) are a class of MNPs categorized as organic nanoparticles. C-MNPs have been under considerable interest in studying in various applications such as magnetic resonance imaging, photothermal therapy, and intracellular transportof drugs. Research work is still largely in progress for testing the efficacy of C-MNPs on the theranostics platform in cellular studies and animal models. In this study, we evaluated the neurobehavioral toxicity parameters on the adult zebrafish (Danio rerio) at either low (1 ppm) or high (10 ppm) concentration level of C-MNPs over a period of two weeks by waterborne exposure. The physical properties of the synthesized C-MNPs were characterized by transmission electron microscopy, Raman, and XRD spectrum characterization. Multiple behavior tests for the novel tank, mirror biting, predator avoidance, conspecific social interaction, shoaling, and analysis of biochemical markers were also conducted to elucidate the corresponding mechanism. Our data demonstrate the waterborne exposure of C-MNPs is less toxic than the uncoated MNPs since neither low nor high concentration C-MNPs elicit toxicity response in behavioral and biochemical tests in adult zebrafish. The approach combining biochemical and neurobehavioral approaches would be helpful for understanding C-MNPs association affecting the bioavailability, biosafety, interaction, and uptake of these C-MNPs in the living organism.

Preparation of molecularly imprinted polymers for sensing of 2,4-dichlorophenoxyacetic acid residues in environmental water and mixed juice

In this paper, we reported a rapid and simple approach to synthesize molecularly imprinted polymers (MIPs) materials for sensing of 2,4-dichlorophenoxyacetic acid (2,4-D) residues in environmental water and mixed juice. Initially, MIPs materials were prepared via visible light-initiated reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization at ambient temperature using 2,4-D and its analogs as template molecules, in which 4-vinyl pyridine (4-VP), ethylene glycol dimethacrylate (EGDMA), (2,4,6-trimethylbenzoyl) diphenylphosphine oxide (TPO), 2-(((dodecylthio)carbonothioyl)thio)-2-methylpropanoic acid (DDMAT) were functional monomer, cross-linker, visible light initiator and RAFT agent, respectively. Then, the morphologies of the MIPs materials were characterized by FT-IR, SEM and DLS. The results showed that the MIPs materials were well-distributed spherical particles with sizes ranging from 1 to 2 μm. Furthermore, a four-channel MIPs sensor array included four polymer microspheres with a fluorescent dye displacement procedure was developed to distinguish the templates and their chemical analogs at the ppm concentration level. With the support of principal component analysis and hierarchical cluster analysis, the four-channel MIPs sensor array proves to be a simple and effective method to recognize and distinguish the templates and nontemplates in aqueous solution with 100% accuracy. Finally, the four-channel MIPs sensor array was also found to have satisfactory accuracy in monitoring 2,4-D contaminated environmental water and mixed juice.

Dynamic pressure gradient modulation for comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry detection

Dynamic pressure gradient modulation (DPGM) is investigated for comprehensive two-dimensional gas chromatography (GC × GC) with time-of-flight mass spectrometry (TOFMS) detection. With DPGM, a commercial pneumatic “pulse” valve is opened to introduce a suitably high auxiliary gas pressure at a T-junction connecting the first dimension (1D) and second dimension (2D) columns during the modulation period (PM), temporarily stopping the 1D flow. The valve is then closed for the duration of a pulse width (pw) to “re-inject” temporally focused 1D eluate onto the 2D column for separation. This flow modulation technique is observed to be compatible with TOFMS detection using a 2D flow rate of 4 ml/min for the separation of a 90-component test mixture. A 25 min separation window using a PM = 1 s and pw = 200 ms for full modulation (and 100% duty cycle) provided an average 1Wb = 4.5 s and 2Wb = 130 ms for a 2D peak capacity of nc,2D = 2700 (100 peaks per min). The detector response enhancement factor (DREF) serves as a metric for the enhanced sensitivity of the modulated relative to the unmodulated 1D peaks, with DREFs ranging between 10 and 20 and about a 5-fold improvement in signal-to-noise ratio (S/N). The bilinear “quality” of the GC × GC data is studied using the chemometric method parallel factor analysis (PARAFAC). Since PARAFAC requires sufficiently trilinear data, the reproducibility of the 2D peak shape for a given analyte is confirmed using lack-of-fit (LOF) and percent variation (R2) metrics. The limit-of-detection (LOD) for the representative analyte hexadecane is determined using PARAFAC, providing an LOD of 0.7 ppb (±0.03 ppb) for three replicates. Seven heavily overlapped analytes are also fully resolved by PARAFAC down to the part-per-million (ppm) concentration level, producing reproducible spectra with a majority of spectral match values (MV) over 800 (RSD ≤ 7.1%). This study provides promising results for DPGM as a flow modulation technique compatible with GC × GC-TOFMS, providing high sensitivity data suitable for chemometric analysis.

On-Line Mixture Quantification to Track Temporal Change of Composition Using FAIMS.

This paper reports on-line mixture quantification with FAIMS. Ternary gas mixtures composed of acetone, ethanol, and diethyl ether were used for quantification. We succeeded in an on-line quantification of ppm-level concentration and even sub-ppm-level gases using the gradient descent method. It took 10 minutes to quantify the ternary mixture. However, it was too long, because we aim to track the temporal change of each component concentration in the mixture. Then, an algorithm based on feedback control was introduced to reduce the quantification time. The feedback method successfully tracked concentrations in three cases. The simulation result shows that the proposed method can reduce the quantification time.

Preliminary Study on the Determination of ppm-Level Concentration of Histamine in Tuna Fish Using a Dry Extract System for Infrared Coupled with Near-Infrared Spectroscopy.

Rapid and simple methods to determine histamine in tuna fish have been examined. A dry extract system for infrared (DESIR) was coupled with near-infrared spectroscopy in order to obtain the absorption of histamine in tuna fish at the ppm level. The result showed that the optimal extraction solvent for preparing DESIR samples was 75% methanol and boiling water (100 °C). Calibration equations were developed and tested by independent validation set samples. The calibration equation developed from boiling water as solvent extraction was slightly better than the equation developed from 75% methanol solvent with a coefficient of determination (R2) of 0.79, a standard error of calibration of 2.45 ppm, a standard error of prediction of 2.94 ppm, and a bias of 0.10 ppm. Furthermore, the predicted values from both equations were not significantly different from the reference values obtained from the standard method at the 95% confidence interval. Compared to the current AOAC fluorometric official method, the proposed technique simplified and reduced the preparation time.

Ecotoxicity Assessment of Fe3O4 Magnetic Nanoparticle Exposure in Adult Zebrafish at an Environmental Pertinent Concentration by Behavioral and Biochemical Testing.

Magnetic Nanoparticles (MNPs) are widely being investigated as novel promising multifunctional agents, specifically in the fields of development for theranostics, electronics, waste water treatment, cosmetics, and energy storage devices. Unique, superior, and indispensable properties of magnetization, heat transfer, and melting temperature make MNPs emerge in the field of therapeutics in future healthcare industries. However, MNPs ecotoxicity as well as behavioral toxicity is still unexplored. Ecotoxicity analysis may assist investigate MNPs uptake mechanism and its influence on bioavailability under a given set of environmental factors, which can be followed to investigate the biomagnification of MNPs in the environment and health risk possessed by them in an ecological food chain. In this study, we attempted to determine the behavioral changes in zebrafishes at low (1 ppm) or high (10 ppm) concentration levels of Fe3O4 MNPs. The synthesized Fe3O4 MNPs sized at 15 nm were characterized by the transmission electron microscope (TEM), the superconducting quantum interference device (SQUID) magnetometer, and the multiple behavior tests for novel tank, mirror biting, conspecific social interaction, shoaling, circadian rhythm, and short-term memory of zebrafish under MNPs chronic exposure were demonstrated. Low concentration MNP exposure did not trigger alteration for majority behavioral and biochemical tests in adult zebrafish. However, tight shoal groups were observed at a high concentration of MNPs exposure along with a modest reduction in fish exploratory behavior and a significant reduction in conspecific social interaction behavior. By using enzyme-linked immunosorbent assays (ELISA), we found a high dose of MNPs exposure significantly elevated cortisol, acetylcholine, and catalase levels while reducing serotonin, acetylcholine esterase, and dopamine levels in the brain. Our data demonstrates chronic MNPs exposure at an environmentally-relevant dose is relatively safe by supporting evidence from an array of behavioral and biochemical tests. This combinational approach using behavioral and biochemical tests would be helpful for understanding the MNPs association with anticipated colloids and particles effecting bioavailability and uptake into cells and organisms.

Highly selective and sensitive turn-on fluorescent sensor for detection of Al3+ based on quinoline-base Schiff base

A new aluminum ion fluorescent probe (4-(diethylamino)-2-hydroxybenzylidene)isoquinoline-1-carbohydrazide (HL1) has been conveniently synthesized and characterized. HL1 exhibited a highly selective and pronounced enhancement for Al3+ in the fluorescence emission over other common cations by forming a 2:1 complex, with a recognition mechanism based on excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT). The strong fluorescent emission can be observed even at ppm level concentration of the probe in the presence of Al3+ with 41 fold intensity enhancement at 545 nm. HL1 displays good linear relationship with Al3+ in the low concentration and the limit of detection is 8.08 × 10−8 mol/L. Similar molecules with different substituents on salicylaldehyde phenyl ring were synthesized for studying the structure-activity relationship. Density-functional theory (DFT) calculations are in agreement with the proposed mechanism. It is confirmed that HL1 could be used to detect Al3+ ions in real sample by fluorescence spectrometry and Al3+ ions in cells by bioimaging.

Reduction of heavy metal from soil in Bakri Landfill, Muar, Johor by using Electrokinetic method

The present study focuses on the contamination levels and distribution of heavy metals in soil samples located at Bakri Landfill area, Muar, Johor, Malaysia. The aim of this study is to determine the type of heavy metal elements that contribute towards soil contamination and to reduce them based on the comparison of elemental analysis between pre and post Electrokinetic (EK) processes. The ppm level concentration of elements in this landfill soil is measured by using X-ray Fluorescence analysis. ICP-MS testing was carried out for liquid samples analysis. There were two set of EK experiments conducted. In first phase, voltage was maintained at 3 Vcm-1 and prolonged for 3 hours, while second phase was operated at 1 Vcm-1 for 48 hours. In this work, distilled water was used as an electrolyte for the process and two identical copper foil were used as electrodes due to high electrical conductivity. The application of EK remediation revealed that successful removal of Rb and Ba elements in the soil were observed by 2-3%, however other heavy metals have not changed.

Direct Mass Spectroscopy Analysis and Comparison of Middle Eastern and Texas Crude Oils

We analyzed two types of crude oil samples: Middle Eastern crude oil and Texas crude oil by using a residual gas analyzer (RGA) based on the linear quadrupole principle. This portable mass analyzer is capable of measuring hydrocarbons with masses of up to 300 atomic mass units (amu) as well as low mass targets, such as methane and carbon dioxide at ppm level concentrations. The generated mass spectra revealed differences in the composition and signal intensity of hydrocarbons of Middle Eastern and Texas crude oil samples. Even if RGA 300 is manufactured to be served as a detailed gas analysis of vacuum systems, we have shown that it is sensitively capable of detection of hydrocarbons and it enables one to qualitative and quantitative analysis of the composition of the crude oils.

In situ chemoresistive sensing in the environmental TEM: probing functional devices and their nanoscale morphology.

In situ transmission electron microscopy provides exciting opportunities to address fundamental questions and technological aspects related to functional nanomaterials, including the structure-property relationships of miniaturized electronic devices. Herein, we report the in situ chemoresistive sensing in the environmental transmission electron microscope (TEM) with a single SnO2 nanowire device, studying the impact of surface functionalization with heterogeneous nanocatalysts. By detecting toxic carbon monoxide (CO) gas at ppm-level concentrations inside the microscope column, the sensing properties of a single SnO2 nanowire were characterized before and after decoration with hybrid Fe-Pd nanocubes. The structural changes of the supported nanoparticles induced by sensor operation were revealed, enabling direct correlation with CO sensing properties. Our novel approach is applicable for a broad range of functional nanomaterials and paves the way for future studies on the relationship between chemoresistive properties and nanoscale morphology.

Trace detection of explosive and their derivatives in stand-off mode using time gated Raman spectroscopy

Trace detection is utmost important for detection of concealed explosive materials in form of IEDs. Surfaces of suspicious objects may be scanned for contamination of explosives. Sensitivity and selectivity are two main concerns in field of explosive detection. Raman spectroscopy provides remarkable selectivity. Time-gated Raman spectroscopy also has potential of providing sensitivity for trace detection. In present study, time-gated Raman spectroscopy investigated for detection of ppm level concentration of explosives. To achieve better sensitivity, various parameters of the experimental set-up like gain of intensifier, number of pulse accumulated and pulse energy of laser were optimised. The trend of change in intensity of Raman scattering (background subtracted) was observed by varying values of these above mentioned parameters. Followed by optimization of these parameters for better sensitivity, Raman spectra of RDX samples at lower concentrations (prepared by mixing RDX with KBr) were recorded. The corrected intensity increased in linear fashion with increase in gain of intensifier, number of pulses accumulated and pulse energy. After that, Raman spectra of RDX were recorded from a stand-off distance of 5m in backscattered mode with concentrations down to 100ppm.

A novel benzidine based Schiff base “turn-on” fluorescent chemosensor for selective recognition of Zn2+

A novel chemo-sensor based on diaminobenzidine (H2L) was synthesized and characterized. The chemo-sensor shows selective “turn-on” fluorescence response to Zn2+ ion over a variety of other competing metal ions such as Al3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, and Cd2+. The strong fluorescent emission can be observed even at ppm level concentration of the probe in the presence of Zn2+ with over 54 fold intensity enhancement at 509nm. Similar fluorescence behaviour is also observed in a variety of solvents and solvent mixtures in the presence of zinc(II). The fluorescent emission is also detected when the H2L sample solution containing Zn2+ is exposed to UV radiation. The sensitive nature of fluorescent response of the probe to Zn2+ is gauged from the very low detection limit of 8.6×10−9M. The chemo-sensor H2L binds to zinc(II) in 1:1 stoichiometry as determined by Job's plot and the binding constant is calculated as 7.8×104M−1.

Induction and Tunability of Self-Healing Property of Dendron Based Hydrogel Using Clay Nanocomposite.

Low molecular weight gels have relatively poor self-healing capacity compared to that of polymeric gels. Induction and tuning of the healing capacity of low molecular weight gels to achieve desired applications are thus challenging tasks. The present work describes the achievement of remarkable tunability of self-healing property for a low molecular weight hybrid gel, based on poly(aryl ether) dendron derivative (PAD). The hybrid gel has been synthesized using PAD and poly(amido amine) {PAMAM} dendrimer derivative (QPD), which are intercalated in the montmorillonite clay (MMT) layers. The self-healing of the hybrid gel (QPD-MMT-PAD) was demonstrated through experiments where the distorted gel regained the initial value of storage modulus (G') within a few minutes. Further, the propensity of self-healing of the gel has been tuned as a function of QPD concentration. The mechanically stable QPD-MMT-PAD hybrid gel has been utilized for the adsorption of ppm level concentration of polycyclic aromatic hydrocarbons (PAHs) such as β-naphthol, pyrene, and phenenathrene from water with excellent efficiency (80-98%).

Ultra-Low NO2 Detection By Gamma WO3 Synthesized By Reactive Spray Deposition Technology

A porous tungsten oxide (WO3) film based NO2 sensor was developed by a one-step flame based process called Reactive Spray Deposition Technology (RSDT). The RSDT process allows the flexibility to create monoclinic gamma-WO3 with control of the particle size, porosity and thickness of the film. This nano-crystalline WO3 film was deposited directly on gold interdigitated electrodes. The sensor response was measured at the parts per million (ppm) level, (0.17-5 ppm in air at 100% relative humidity) at different operating temperatures (250-350°C) to determine the optimum working temperature. The sensitivity was found to be maximum at 300 °C. The sensors showed a relatively fast response time (∼7s) and recovery time (∼5 min), respectively. The stability of the sensor was evaluated for 300 h in 0.5 ppm NO2 in air at 100% relative humidity (2000 response-recovery cycles). The sensor was stable up to 6 days (~150 h) of continuous operation and degraded between 150 to 300 h. In order to check the selectivity, the sensor was also tested for 10 ppm acetone, 100 ppm ethanol, 10-100 ppm H2, and 10 ppm isoprene. Interference was negligible with 10 ppm acetone, 100 ppm ethanol, 10 ppm H2 and humidity; however, it was significant with 10 ppm isoprene and 100 ppm H2. We have also compared the test data of this gamma WO3 based NO2 sensor prepared by RSDT with the results reported in the literature. The morphology and surface properties of the WO3 film were investigated with XRD, Raman spectroscopy, BET, SEM, TEM, and HRTEM. Here we will provide a brief description of the synthesis, fabrication and testing procedure of the NO2 sensor. The microstructure of the tungsten oxide films, and the effect of the film structure, grain size, and the sensor response to the ppm level concentration of NO2 will be described. The sensing mechanism with emphasis to adsorption and desorption will be explained in details.

Gas-Sensing Properties of Pt-V<sub>2</sub>O<sub>5</sub> Thin Films for Ethanol Detection

In the present work, vanadium pentoxide (V2O5) nanoparticles have been investigated for monitoring ethanol (C2H5OH) at ppm levels in air. A one-step flame spray pyrolysis (FSP) process has been applied for the synthesis of vanadium pentoxide (V2O5) and platinum-loaded vanadium pentoxide (Pt-V2O5) nanoparticles. The samples have been studied to characterize their morphological and microstructural properties by X-ray diffraction and transmission electron microscopy. Pt addition to V2O5 samples were verified by energy dispersive X-ray spectrometry mode. The specific surface area of the nanoparticles was measured by nitrogen adsorption method. The application of the produced nanoparticles as sensitive and selective ethanol resistive sensor has been demonstrated. The Pt-loaded V2O5 sensor has shown higher response towards ethanol at ppm-level concentrations compared to unloaded one.

Phosphine induced Nickel Migration in SOFC Anodes: A Computational Study

The poisoning of anode materials by impurities in coal syngas is a significant problem for utilization of coal syngas in Solid Oxide Fuel Cells (SOFCs). One such impurity, phosphine is known to cause catastrophic failure of SOFC anode at ppm level concentrations. A significant phenomenon observed in SOFC anodes, made of Ni-YSZ cermets, when exposed to phosphine is migration of the nickel from porous matrix towards the surface, which is believed to be one of the reasons for performance degradation. The mechanisms responsible for the experimentally observed nickel migration are not well understood. In this study, a plausible mechanism is proposed to reveal the effect of electrical current and steam concentration on nickel migration in SOFC anodes. A physics based transport model for nickel migration is formulated based on the electro-migration, formation of the secondary phases and diffusion. This model is integrated into a readily available one dimensional in house code for predicting SOFC anode degradation due to fuel impurities. Simulations show that the proposed mechanism of Ni diffusion driven by secondary phase formation, the electrical force, and humidity can reveal the experimentally observed accumulation of Ni and secondary phases on the SOFC anode surface.

English

A phase-shift cavity ring-down spectroscopy (PS-CRDS) experimental set-up has been established using a broadband diode laser for the measurement of phase shift due to absorption of NO 2 in a sealed off cavity ringdown cell. The PS-CRDS technique is verified by optimising various parameters of CRDS cavity and excitation laser. The PS-CRDS signals were measured on the first harmonics using a lock-in-amplifier. The square modulated laser pulses were used in the experiment to obtain the decay time. Measurements of the signal strengths at different CRDS cavity lengths wre also carried out to verify the detection sensitivity for ppm level concentration measurement of trace gases.

The effects of activated carbon surface features on the reactive adsorption of carbamazepine and sulfamethoxazole

Two commercial carbons, coconut shell- and wood-based were chosen to evaluate the mechanisms of carbamazepine (CBZ) and sulfamethoxazole (SMX) adsorption from a low (ppm level) concentration of these pharmaceuticals. The initial sample and those after adsorption were extensively characterized using potentiometric titration, thermal analysis combined with mass spectroscopy, FTIR, and XPS. It was found that not only porosity but also surface chemistry plays an important role in the adsorption process. The results show that extensive surface reactions take place during adsorption and adsorbates undergo significant transformations in the pore system. The ability of carbon surfaces to form superoxide ions results in the oxidation of CBZ and SMX, and their partial decomposition. Surface chemistry also promotes dimerization of the latter species. Moreover, functional groups of CBZ and SMX, mainly amines, react with oxygen groups of the carbon surface. Thus not only microporous carbons with sizes of pores similar to those of adsorbate molecules, but the carbons with large pores, rich in oxygen groups, can efficiently remove these pharmaceuticals following the reactive adsorption mechanism.

A Computational Study of Nickel Migration in SOFCs Anode Due to Phosphine Induced Degradation and Applied Electrical Current

The poisoning of Solid Oxide Fuel Cells (SOFCs) anode materials by impurities in coal syngas is a significant problem for utilization coal symgas in SOFCs. One such impurity, phosphine is known to cause catastrophic failure of SOFC anode at ppm level concentrations (below 10 ppm). A significant phenomenon observed in SOFC anodes, made of Ni-YSZ cermets, exposed to phosphine is migration of the nickel from porous matrix to the surface, which is believed to be one of the reasons for performance degradation. The mechanisms responsible for the experimentally observed Nickel migration are not well understood. A possible mechanism, which considers the Nickel diffusion and the formation of secondary phases (Ni-P compounds) as responsible phenomenon of Nickel migration, was proposed by our group. However this consideration does not allow us to predict the experimentally observed effect of the applied current. In this study, a reasonable mechanism is proposed to reveal the effect of electrical current on Nickel migration in SOFCs. The postulation of this mechanism is that the applied electrical current could possibly cause the transport of Nickel by generating an electrical force in the current flow direction. In SOFCs, the electrical current flows from anode/electrolyte interface to anode/fuel interface. Therefore the direction of the Nickel transport is from anode active layer to the anode surface. A transport model for nickel migration is formulated based on these postulations and it is integrated into an existing one dimensional in house code for predicting SOFC anode degradation due to fuel impurities. Simulations show that the proposed mechanism of Ni diffusion driven by secondary phase formation and the electrical force can reveal the experimentally observed accumulation of Ni and secondary phases on the SOFC anode surface when driven by a current and exposed to phosphine.