Vapor Samples Research Articles

Detection of anabolic androgenic steroids in serum samples.

When testing for anabolic androgenic steroids (AAS) outside sports communities, for example, in healthcare and forensic medicine, urine is the matrix of choice. However, there are drawbacks with urinary sampling, and serum might be useful as a complementary matrix. The aim was to develop an LC-MS/MS method for serum measuring AAS frequently used outside of sport, including testosterone (T), steroid esters, and eight other synthetic AAS. The sample pretreatment included sample precipitation and evaporation. Limit of quantification for the AAS was 0.05-0.5ng/mL, and linearity was 0.05-20 ng/mL for most of the substances. Generally, the within- and between-day CV results, matrix effect, and process efficiency were <15%. The AAS were stable for at least 6months at -20°C. Serum samples were obtained from previous studies. A novel finding from an administration study was that T enanthate was present in serum even after 5years of storage at -20°C. Serum samples from self-reporting AAS individuals, where T esters were detected, were positive for testosterone using the urinary testosterone/epitestosterone criterion >10. Of those identified as positive in traditional urinary doping tests (n = 15), AAS in serum were found in 80% of the subjects. Our results show that serum may be a valid complementary matrix to urine samples for AAS testing.

Rapid on-site detection of underground petroleum pipeline leaks and risk assessment using portable gas chromatography-mass spectrometry and solid phase microextraction

Locating underground pipeline leaks can be challenging due to their hidden nature and variable terrain conditions. To sample soil gas, solid-phase microextraction (SPME) was employed, and a portable gas chromatography/mass spectrometry (GC/MS) was used to detect the presence and concentrations of petroleum hydrocarbon volatile organic compounds (pH-VOCs), including benzene, toluene, ethylbenzene, and xylene (BTEX). We optimized the extraction method through benchtop studies using SPME. The appropriate fibre materials and exposure time were selected for each BTEX compound. Before applying SPME, we preconditioned the soil vapour samples by keeping the temperature at around 4 °C and using ethanol as a desorbing agent and moisture filters to minimize the impact of moisture. To conduct this optimisation, airbags were applied to condition the soil vapour samples and SPME sampling. By conditioning the samples using this method, we were able to improve analytical efficiency and accuracy while minimizing environmental impacts, resulting in more reliable research data in the field. The study employed portable GC/MS data to assess the concentration distribution of BTEX in soil vapour samples obtained from 1.5 m below the ground surface at 10 subsurface vapour monitoring locations at the leak site. After optimization, the detection limits of BTEX were almost 100 µg/m3, and the measurement repeatabilities were approximately 5% and 15% for BTEX standards in the laboratory and soil vapour samples in the field, respectively. The soil vapour samples showed a hotspot region with high BTEX concentrations, reaching 30 mg/m3, indicating a diesel return pipeline leak caused by a gasket failure in a flange. The prompt detection of the leak source was critical in minimizing environmental impact and worker safety hazards.

Development of dispersive liquid-liquid microextraction with solid-phase evaporation as a novel hyphenated method prior to ion mobility spectrometry and its application for trace analysis of fluoxetine.

For the hyphenating of dispersive liquid-liquid microextraction (DLLME) with nano mesoporous solid-phase evaporation (SPEV) as a novel method, MCM-41@SiO2 was synthesized and used as a nano mesoporous adsorbent for coating on the solid-phase fiber, preconcentration of fluoxetine antidepressant drug (as a model compound), and total evaporation of the extraction solvents obtained by the DLLME method. To detect the analyte molecules, a corona discharge ionization-ion mobility spectrometer (CD-IMS) was applied. In order to increase the extraction efficiency and the IMS signal of the fluoxetine drug, some variables including extraction solvent and its volume, disperser solvents and its volume, sample solution pH, desorption temperature, and evaporation time of the solvent from the solid-phase fiber were chosen and optimized. Some analytical parameters including limit of detection (LOD), limit of quantification (LOQ), linear dynamic range (LDR) with determination coefficient, and relative standard deviations (RSDs) were calculated under the optimized conditions. LOD (S/N = 3), 3ngmL-1; LOQ (S/N = 10), 10ngmL-1; LDR, 10-200ngmL-1; and intra- and inter-day RSDs (n = 3), 2.5% and 9.6% for 10ngmL-1, and 1.8% and 7.7% for 150ngmL-1, respectively. To investigate the ability of the hyphenated method to determine fluoxetine in real samples, fluoxetine tablets, and some biological samples such as human urine and blood plasma were selected and the relative recovery values were calculated to be 85-110%. The accuracy of the proposed method was compared with that of the HPLC standard method.

Lightweight Gas Sensor Based on MEMS Pre-Concentration and Infrared Absorption Spectroscopy Inside a Hollow Fiber

This paper reports on a compact and lightweight sensor for analysis of gases/vapors by means of a MEMS-based pre-concentrator coupled to a miniaturized infrared absorption spectroscopy (IRAS) module. The pre-concentrator was utilized to sample and trap vapors in a MEMS cartridge filled with sorbent material and to release them once concentrated by fast thermal desorption. It was also equipped with a photoionization detector for in-line detection and monitoring of the sampled concentration. The vapors released by the MEMS pre-concentrator are injected into a hollow fiber, which acts as the analysis cell of the IRAS module. The miniaturized internal volume of the hollow fiber of about 20 microliters keeps the vapors concentrated for analysis, thus allowing measurement of their infrared absorption spectrum with a signal to noise ratio high enough to identify the molecule, despite the short optical path, starting from sampled concentration in air down to parts per million. Results obtained for ammonia, sulfur hexafluoride, ethanol and isopropanol are reported to illustrate the sensor detection and identification capability. A limit of identification (LoI) of about 10 parts per million was validated in the lab for ammonia. The lightweight and low power consumption design of the sensor allowed operation onboard unmanned aerial vehicles (UAVs). The first prototype was developed within the EU Horizon 2020 project ROCSAFE for the remote assessment and forensic examination of a scene in the aftermath of industrial or terroristic accidents.

Investigation on the influence of a titanium coating on the aging behavior of ATZ ceramics for implant applications

The aim of this investigation was to determine the influence of a metallic coating on the LTD behavior of an ATZ ceramic. Therefore, a 300 μm thick titanium layer was deposited by plasma spraying on a commercial ATZ ceramic containing 20 wt% alumina and 80 wt% 3Y-TZP. After aging the coated and uncoated samples in water vapor at 134 °C and 2 bar for 5 h and 30 h, respectively, the monoclinic phase content was determined using X-ray diffraction, and its impact on the mechanical properties was assessed in biaxial flexural strength tests. The results revealed an increase in strength with increasing aging time. Furthermore, the Ti-VPS-coating slows down the aging of the ceramic because it acts as a diffusion barrier for the hydroxide ions. As a result, after 30 h of aging, the monoclinic phase content of the coated samples is up to 30% lower than of the uncoated samples.

Reproducible measurements of the δ2H composition of non-exchangeable hydrogen in complex organic materials using the UniPrep2 online static vapour equilibration and sample drying system

Non-exchangeable hydrogen-isotope (δ2Hn) measurements of complex organic samples are used in forensics to determine sample authenticity, traceability, and provenance. However, δ2Hn assays of organics are usually complicated by uncontrolled “exchangeable hydrogen” and residual moisture contamination; hence, δ2Hn assays are persistently incomparable amongst laboratories. We introduce a revised technical solution (UniPrep2) to control hydrogen-isotope exchange and for robust online sample drying and vapour equilibration. The UniPrep2 device is coupled to a high-temperature thermochemical elemental analyser and continuous-flow isotope-ratio mass spectrometer. This technical solution empowers isotope analysts to:•Conduct reproducible controlled vapour equilibrations of complex organic samples and standards to determine the δ2Hn values by controlling hydrogen-isotope exchange.•Conduct online vacuum-oven evacuation with extensive helium drying without exposure to air to reabsorb or exchange hydrogen with ambient water vapour.The protocol describes the operation of the UniPrep2 device and the step-by-step procedures needed to obtain accurate and precise δ2Hn values for a wide range of organic sample types. Two analytical approaches are described in detail; the Dual-Vapour Equilibration (DVE) approach, intended for determining δ2Hn for a complex organic environmental sample where matrix equivalent H isotope reference materials are not available, and the Comparative Equilibration (CE) approach, which is intended for routine high-throughput analyses of complex organic samples where at least two matrix-equivalent organic isotope reference materials with consensus δ2Hn values are being used. These standard operating procedures are envisioned to be a sound basis for advancing hydrogen-isotope analysis for different organic environmental matrices and studies.

Modeling of saturated steam selection methods at various medium pressures

The article presents the results of modeling methods for selecting saturated steam at different pressures in low, medium, and high-pressure boilers. The aim of the research is to identify the cause of a violation of the representativeness of the sample by modeling the selection of saturated steam by three selection structures at different pressures. The main requirements for sampling devices are considered, including: optimization of the design of the device for sampling saturated steam, observance of isokinetic sampling, and minimization of abrupt changes in pressure and temperature of the sample taken. It is noted that the design of the sampling device should minimize the amount of stagnant zones in the sampling device and promote the maintenance of flow velocity in the sampling device. The importance of maintaining equal flow velocities in the pipeline and the sampling device is shown to be important when sampling saturated steam to avoid two-phase fluid stratification and steam condensation. It is revealed that the prevention of changes in the pressure and temperature of the saturated vapor sample in sampling devices leads to the provision of constant concentrations of impurities in the vapor. The results of simulation of saturated steam flow sampling in a low-pressure boiler using a single-strip sampling device, in a high-pressure boiler using a outlet probe and in a medium-pressure boiler - without a sampling device are presented. The modeling results showed non-compliance with the equality of flow velocities in all three sampling devices at different pressures, and the formation of a film on the surface of all three sampling devices. The need to comply with the main requirements for sampling saturated steam to ensure the representativeness of the sample by maintaining isokinetic flow, minimizing stagnant zones, and avoiding changes in pressure during sampling is confirmed.

Determination of Radiocarbon Content in Bio-Oil Samples by Mini Carbon Dating System in the Gliwice Radiocarbon and Mass Spectrometry Laboratory

Abstract The applications of isotopes are used by many European countries to investigate environmental changes. A compact modern accelerator mass spectrometry (AMS) system known as Mini Carbon Dating System (MICADAS) is used in Gliwice Radiocarbon and Mass Spectrometry Laboratory for determining the 14C content in different environmental samples including liquid fuels. For radiocarbon measurement using MICADAS, the liquid samples are accurately prepared using the tin capsules for liquids for combustion in elemental analyser (EA) and graphitisation in the AGE system. In this study, the determination of 14C content in three different bio-oil samples and one reference sample of 100% biomass was conducted. Bio-oil samples were prepared using tin capsules for liquids sealed in the second capsules for solids to avoid sample evaporation while the reference sample was prepared using the tin capsule for solids for combustion in EA and graphitisation in the AGE system. Based on the 14C measurement results, one of the bio-oils was not produced from the analysed reference biomass. Two others were determined as a mixture of bio- and fossil components, and based on 14C the bio-carbon content was calculated. For all samples, the 14C measurement showed reproducible and reliable results.

Sub-nL thin-film differential scanning calorimetry chip for rapid thermal analysis of liquid samples.

Differential scanning calorimetry (DSC) is a popular thermal analysis technique. The miniaturization of DSC on chip as thin-film DSC (tfDSC) has been pioneered for the analysis of ultrathin polymer films at temperature scan rates and sensitivities far superior to those attainable with DSC instruments. The adoption of tfDSC chips for the analysis of liquid samples is, however, confronted with various issues including sample evaporation due to the lack of sealed enclosures. Although the subsequent integration of enclosures has been demonstrated in various designs, rarely did those designs exceed the scan rates of DSC instruments mainly because of their bulky features and requirement for exterior heating. Here, we present a tfDSC chip featuring sub-nL thin-film enclosures integrated with resistance temperature detectors (RTDs) and heaters. The chip attains an unprecedented sensitivity of 11 V W-1 and a rapid time constant of 600 ms owing to its low-addenda design and residual heat conduction (∼6 μW K-1). We present results on the phase transition of common liquid crystals which we leverage to calibrate the RTDs and characterize the thermal lag with scan rates up to 900 °C min-1. We then present results on the heat denaturation of lysozyme at various pH values, concentrations, and scan rates. The chip can provide excess heat capacity peaks and enthalpy change steps without much alteration induced by the thermal lag at elevated scan rates up to 100 °C min-1, which is an order of magnitude faster than those of many chip counterparts.

Forensic Analytical Approach for Hydrocarbon Fingerprinting in Soil Vapor Samplings: Example of a Residential Neighborhood in Brazil

Conventional analytical methods determine the concentration of compounds used to estimate the presence of environmental contamination capable of posing risk to human and ecological receptors (Murphy and Morrison, 2007). While these target analytes help regulators and environmental professional identify and manage potentially harmful conditions, these compounds can be generated by many natural and anthropogenic (man-made) sources and conventional methods alone fail to compositionally differentiate subsurface sources of contamination in complex environments (Morrison, 2000; Wang and Fingas, 2003; Gouvêa et al, 2019; Douglas et al, 2007). This case study demonstrates the advantage of using both conventional and forensic testing methods to accurately identify the source(s) of volatile hydrocarbon contamination in soil vapor samples for the development of an accurate conceptual site model in a neighbourhood near industrial facilities in Rio de Janeiro State, Brazil. The goal of this study was to differentiate potential impacts from a local steelmaking plant from fugitive hydrocarbons associated with more generic human activity in urban settings. This case study demonstrated the advantage of constructing chemical fingerprints from conventional volatile organic compound (VOC) method TO 15 and a forensic volatile hydrocarbon method using an enhanced version of method TO 15 (PIANO). The chemical fingerprints of vapor samples collected from subsurface soil gas and sewers were analysed and compared to laboratory reference samples. These data determined that the VOCs detected in neighbourhood soil vapor samples were associated with fugitive petroleum products migrating in the sewer pipelines and not with the steelmaking wastes emplaced near the residential area. This article discusses the forensic data and chemical signatures that support these findings, and the use of environmental forensic techniques to evaluate environmental data associated with complex scenarios, involving multiple contamination sources.

Adsorption processes on a carbonaceous surface: Electron spin resonance study

The effect of pyrolysis at T ∼700 °C of the low-rank coal samples was studied using scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), and Raman scattering of light methods. The kinetics of adsorption-desorption processes on a carbon surface was first investigated based on the dynamics of the spin characteristics of paramagnetic defects (carbon dangling bonds). The EPR signals of these defects in the air are characterized by the anomalously large broadening up to ΔBpp = 32 mT, nearly two orders of magnitude in comparison with the initial samples. It is established that broadening is caused by the interaction of the spins of defects with molecular oxygen. The latter is adsorbed on the surface of the samples in a high concentration because the samples have a high porosity formed with the participation of ash nanoclusters, including FexOy. The observed EPR dynamics are very complex. It depends on the initial conditions of signal observation, the occurrence of other gases, e.g. nitrogen, and drastically on the humidity of the environment. For example, holding samples in the water vapor at T = 100 °C reduces the ΔBpp from ∼17.5 mT to 3.2 mT for a time of nearly t ∼24 s. Using the strong effect of oxygen on the broadening of the studied samples, the kinetics of competitive processes of adsorption/desorption of N2↔O2↔H2O on the carbon surface is studied in detail. The unusual adsorption kinetics for the mixture of O2 and N2 gases, caused by a difference in the diffusion rates, was found.

Comprehensive analysis of hydrogen production from various water types using plasma: Water vapour decomposition in the presence of ammonia and novel reaction kinetics analysis

The interest in nonthermal discharge plasma has recently increased over the last few decades due to the ability to generate new radicals at atmospheric pressure. This paper presents a comprehensive analysis of the dissociation processes and reaction rates of various water vapour samples by dielectric barrier discharge plasma (DBD). The influence of water contamination and the presence of ammonia (NH3) on hydrogen production from water vapour was investigated. A novel reaction rate expression was proposed to fit the plasma-water vapour experiment results. The hydrogen production and conversion rate of pure reverse osmosis (RO) water samples showed greater results than the contaminated water samples in all experiments at different tested bubbling temperatures. The higher conversion rate was obtained from RO water combined with 1%NH3 at a bubbling temperature of 50 °C and was 1.17%. The water contamination influenced the generated DBD plasma micro discharges, consequently decreasing the electron collisions, leading to lower water vapour conversion into constituent elements H2 and O2. It was also found that the influence of ammonia on the water vapour decomposition was related to the NH3 concentration. Moreover, the reaction rate showed good agreement with the experimental results. It was observed that the energy efficiencies were obtained at an operating temperature of 50 °C for pure RO, GTW, and CTW water samples enhanced by adding 1%NH3, for example, the RO energy efficiency value at a bubbling temperature of 50 °C increased from 0.133% to 1.15% because of more hydrogen was generated. It implies that the water vapour decomposition processes are influenced by the following parameters: input gas temperature, reaction time, plasma power, oven or reactor heating temperature, the separation method, sampling method, and sampling collection time.

At-Line Sampling and Characterization of Pyrolytic Vapors from Biomass Feedstock Blends Using SPME-GC/MS-PCA: Influence of Char on Fast Pyrolysis.

Solid-phase microextraction (SPME) coupled with gas chromatography-mass spectrometry (GC-MS) analysis was used for the at-line sampling of pyrolytic vapors produced during the fast pyrolysis of biomass. The pure and binary blends of switchgrass (SWG) and pine harvest residues (PT6) were used as biomass feedstocks. Sequential SPME sampling allowed for monitoring of changes in the pyrolysis vapors as char accumulated in the fluid bed. The relative concentration and composition of the pyrolysis vapors desorbed from the SPME fibers were investigated using GC-MS, and the resulting chromatograms were analyzed using principal component analysis (PCA) to compare the composition of the pyrolysis vapors over the course of the pyrolysis run. The chemical compositions of both carbohydrate and lignin fragments varied as the char builds up in the reactor bed. Fragments derived from cellulose and hemicelluloses included anhydrosugars, furans, and light-oxygenated compounds. Lignin fragments included methoxyphenols, phenolic ketones, aldehydes, and low-molecular-weight aromatics. The composition of the carbohydrate fragments changed more than those of the lignin fragments as the char built up in the fluid bed. This combination of SPME-GC/MS-PCA was a novel, easy, and effective method for measuring the composition and changes in the composition of pyrolysis vapors during the fast pyrolysis process. This work also highlighted the effect of char build-up on the composition of the overall pyrolysis vapors.

Real-Time Experimental Monitoring for Water Absorption Evolution Behaviors of Sandstone in Mogao Grottoes, China

Rock mass has typical pore structure, and the induced coupling effects of fluid and solid matrix appear in the disaster evolution process of deep energy exploitation and overground rock hydration. As a representative case, influenced by the water absorption environment, the surrounding rock and murals of Mogao Grottoes produce hydration diseases, which may be related to unclear interaction mechanisms between the surrounding rock and water. In this study, the self-developed physical experimental system for real-time experimental monitoring was applied to test the water absorption evolution behaviors of sandstone. The experimental results showed that the water evaporation of the rock sample during the process of water absorption could be measured through this well-designed physical experimental system, and the actual water absorption of the rock sample is the difference between the decrease of water in the water storage bucket, measured by the balance and the water evaporation in the process of experiment; by drawing the actual water absorption curve of the rock sample, the time when the water absorption of the rock sample reaches saturation could be determined accurately; and the curve of water absorption with time could be expressed as an exponential function. The experimental techniques and methods in this study provide a feasible research idea for studying the water absorption evolution behaviors and mechanisms of the surrounding rock weathering when it meets water, and have significance for revealing the disease mechanisms of the surrounding sandstone in Mogao Grottoes, China.

A highly reusable fluorescent nanofilm sensor enables high-performance detection of ClO2

As the most effective disinfectant, the safe-use of ClO2 is based on proper concentrations. A big challenge in the determination of ClO2 lies in reusability owing to its strong oxidative property. Herein, we report for the first time a nanofilm-based fluorescent sensor towards the high-performance detection of ClO2. The nanofilm was prepared via interfacially confined dynamic covalent condensation of a fluorescent o-carborane derivative (CB-2CHO) and calix[4]arenetetrahydrazide (CATH). The nanofilm as obtained is smooth and uniform. The thickness can be tuned at least from 80 nm to 400 nm. Meanwhile, the nanofilm is photochemically stable, and shows a Stocks shift of 193 nm. A fluorescent sensor constructed with the nanofilm depicted fast, sensitive, selective, and fully reversible sensing to ClO2 vapor in air. Moreover, non-invasive detection of the chemical in aqueous phase with a detection limit of ∼0.85 mg/L was realized via vapor sampling from the headspace of the solution. The linear range is from a few to 5000 mg/L.

(Invited) Carbon Nanotube-Based Fabric Sensor for Selective Sodium Detection in Sweat

Despite the recent advancements in sensor detection of biomarkers in sweat, there is no sensor capable of long-term detection in constricted or load-bearing applications where other flexible plastic sensors might cause discomfort. In this work, a carbon nanotube-based fabric sensor capable of real-time detection of sodium in human sweat is presented. The sensor consists of an electrospun nylon-6 base functionalized with multi-walled carbon nanotubes for enhanced conductivity and p-tert-calix[4]arene for enhanced sodium selectivity. Monitoring sweat is a compelling choice to gain insight into a person’s hydration at a molecular level, as sweat is rich in physiological and metabolic information that can be obtained non-invasively. Body surface sweat is approximately 99% water but also contains over 40 other compounds, most notably the presence of extracellular ions: sodium and chloride. Sodium has been shown to have a notable correlation to body fluid balance and is lost in ample quantities during exercise, making it a promising candidate for the detection of dehydration (i.e., hypernatremia) and overhydration (i.e., hyponatremia). Other compounds commonly found in surface sweat include intracellular ions, metabolites, hormones, small proteins, and peptides. This rich composition and its correspondence to blood chemistry can be the key to accessing the body’s biomolecular (health) state through non-invasive monitoring and diagnostics.When monitoring biomarkers in sweat, the sampling step has the greatest impact on accuracy. Traditional methods for monitoring sweat sodium concentration involve collecting a sweat sample and performing chemical analysis in two separate steps. Typical sweat collection procedures include whole body washdown, sweat collection patches, arm bags, and Macroducts® which require some combination of tedious procedures, trained professionals, and large equipment for analysis. These methods are often limited by insufficient sample volumes, non-negligible sample evaporation, possible analyte degradation between sampling and analysis all of which strongly impacts the reliability and sensitivity of the measurement.To circumvent the problems caused by separating sampling and analysis, sweat sampling can also be completed using wearable sensors. Through in-situ sampling and analysis, wearable sweat sensors can perform the necessary real-time measurements with freshly generated sweat rather than a mixture of new and old sweat. Functional absorbent materials (e.g., paper, nonwoven, cellulosic, or hydrogels) are typically introduced between the skin and the sensing component; although as shown in this work, they can also be introduced as sensing components during sampling. The advantages of functional absorbent sensing materials are their low cost, multiple functions, real-time and continuous sensing, and most importantly the enhanced breathability of sweat glands. As such, these wearable sensors avoid the issue of altering the sweat composition underneath because they remove the old sweat accumulation as new sweat wicks into the material and washes away old sweat. This also allows physiological monitoring for longer periods of time than traditional epidermal microfluidic devices. Additionally, functional absorbent materials can also be integrated into fabrics with inherent moisture wicking properties to bring sweat to a sensing area.This work presents the characterization and on-body testing of a previously developed functional absorbent material sensor made of a multi-walled carbon nanotube (MWCNT) functionalized nylon-6 nanocomposite. The wearable-fabric sensor works by measuring resistance of the nanocomposite material as sodium binds to the sensor fabric. The functionalization of the nanocomposite material was verified by FTIR; while XRD spectra show that the electrospun nylon-6 is made of -form crystals and the resulting nanocomposite is intercalated/exfoliated with an increase in crystalline size. The optimized MWCNT/nylon-6 nanocomposite sensor has a MWCNT loading close to the percolation threshold at approximately 1-2 wt%. Experimental results demonstrated that the sensor is selective to sodium in sweat at a sensitivity of 10 mM sodium. When worn on the body (attached to human skin), the sensor is capable of real-time monitoring of sodium concentration in sweat in the physiologically relevant range of 10-110 mM with up to 95% accuracy. Additionally, the obtained signal can be sent out via Bluetooth so that changes in hydration status can be detected in real-time. Overall, this carbon nanotube-based fabric sensor can be integrated into “smarter” clothing to read an array of biomarkers in sweat. This could lead to better understanding of health and disease processes (e.g., analysis of common diabetic neurological complications, diagnosis of cystic fibrosis (CF), sweat monitoring for advanced prosthetic limb applications and bedridden patients, and athlete performance tracking) resulting in better treatments and health outcomes for all patients. Figure 1

Acetone sensing in liquid and gas phases using cyclic voltammetry

This paper presents the use of cyclic voltammetry to measure acetone concentration in liquid and vapor forms at disposable screen-printed electrodes of platinum working electrode, platinum counter electrode, and silver/silver chloride reference electrode. The main characteristics of the acetone sensor including its linearity, sensitivity, reproducibility, and limit of detection (LOD) were studied by doing different experiments to test both liquid and vapor samples in the physiological range of 1 µM to 10 mM. The change in acetone concentration was monitored by comparing the lineshape of butterfly region before and after injecting the acetone sample in the baseline solution that contains 0.5 M H2SO4. The sensor was shown to have a good sensitivity, reproducibility, and a linear response with respect to the acetone concentration in both liquid and gas phases over a range of 1 µM to 10 mM with R2 > 0.97 and LOD of 0.1 µM. The system stability was improved by building a closed glass system to reduce the exchange of acetone with the surrounding air in an open environment. The closed system was tested using vapor samples and the error bars in the calibration curve were reduced to more than half of their values before using the closed system. The new system will be used extensively in future for an enzyme-based acetone sensor that will be used for diabetes monitoring.

Terahertz characterization of graphene conductivity via time-domain reflection spectroscopy on metal-backed dielectric substrates

A theoretical and experimental framework for the characterization of the terahertz (THz) conductivity of graphene on metal-backed substrates is presented. Analytical equations are derived for the general problem of oblique incidence of the THz beam in a time-domain spectroscopic (TDS) setup working in reflection. The recorded time-domain signals are post-processed in order to retrieve the substrate thickness, its dielectric frequency dispersion, and the complex graphene conductivity frequency dispersion, which is described by a generalized Drude–Smith model. The method is tested on two samples of chemical vapor deposited graphene, transferred on polyethylene terephthalate and cyclo-olefin polymeric substrates of sub-millimetric thickness, and characterized by Raman spectroscopy. By working only with the amplitude spectra, the proposed method circumvents issues stemming from phase uncertainties that typically affect TDS measurements in reflection mode. More important, it allows for a rapid, nondestructive characterization of graphene sheets that can be directly integrated in the production flow of graphene-based passive or active components employing metal-backed resonant cavities, such as THz absorbers, metasurface lenses, or leaky-wave antennas.

Using of electrothermal vaporization for direct analysis of zinc solid samples by two-jet arc plasma optical emission spectrometry

The technique of the direct analysis of zinc solid samples by two-jet arc plasma optical emission spectrometry (TJP-OES) with electrothermal vaporization (ETV) of samples is developed. Vaporization of sample matrix (zinc) and analytes from graphite tube during different temperature programs is investigated. The matrix influences from zinc on the signals of analytes are studied in detail. It has been shown that the simultaneous vaporization of analytes and sample matrix makes it possible to determine the content of the largest number of analytes elements with insignificant matrix effects. The results of optimization of instrumental parameters of TJP-OES analysis are presented. The technique of direct ETV-TJP-OES analysis of zinc provides limits of detection (LODs) of Ag, Al, Au, B, Ba, Be, Ca, Co, Cr, Fe, Ga, Mg, Mn, Ni, Re, Sn and Sr from 0.05 to 100 ng g−1. Due to the high efficiency of ETV for the sample introduction the LODs of most analytes were improved from 2 to 20 times comparing to the TJP-OES with standard sample introduction system.

A field-portable colorimetric method for the measurement of peracetic acid vapors: a comparison of glass and plastic impingers

A method for measuring peracetic acid vapors in air using impinger sampling and field-portable colorimetric analysis is presented. The capture efficiency of aqueous media in glass and plastic impingers was evaluated when used for peracetic acid vapor sampling. Measurement of peracetic acid was done using an N,N-diethyl-p-phenylenediamine colorimetric method with a field-portable spectrometer. The linearity of the N,N-diethyl-p-phenylenediamine method was determined for peracetic acid both in solution and captured from vapor phase using glass or plastic impingers. The Limits of Detection for the glass and plastic impingers were 0.24 mg/m3 and 0.28 mg/m3, respectively, for a 15 L air sample. The Limits of Quantitation were 0.79 mg/m3 and 0.92 mg/m3 for the glass and plastic impingers, respectively. Both metrics were below the American Conference of Governmental Industrial Hygienists Threshold Limit Value Short-Term Exposure Limit of 1.24 mg/m3 (0.4 ppmv) during a 15-min period. The impinger sampling method presented herein allows for an easy-to-use and rapid in-field measurement that can be used for evaluating occupational exposure to peracetic acid.