Polar Volatile Organic Compounds Research Articles

Efficient and sensitive quantification of polar tobacco volatile organic compounds by a micro thermal-assisted sampling device using reduced graphene oxide coupling with thermal desorption-gas chromatography/mass spectrometry

AbstractIt still remains a great challenge to selectively enrich and sensitively quantify the trace volatile organic compounds (VOCs) in real samples with complex matrix. In this study, an integration method combining a selective enrichment medium of reduced graphene oxide (rGO) with a specially designed micro thermal-assisted purge-and-trap sampling device was developed for efficient enrichment and sensitive quantification of trace tobacco VOCs coupling with thermal desorption (TD)-gas chromatography/mass spectrometry (GC/MS). The prepared rGO has been proved to possess excellent enrichment selectivity and capacity for tobacco polar VOCs with the multi-layer structure, good thermal stability and large specific surface area. The specially designed sampling device was efficient and suitable for enriching and sampling trace polar tobacco VOCs coupling with rGO medium. Under the optimized sampling and analytical conditions, the established analytical method could be actually applied for quantification of typical tobacco polar VOCs with the good recoveries of 72.9–128% and the satisfied RSDs of 1.8–19.9% (n = 3). The results suggested that the developed method was selective, sensitive and reliable for enrichment and quantification of trace tobacco polar VOCs.

Current Concepts towards the Health Hazards of BBQ Smoke and Newer Possibilities for Risk Mitigation: A Pilot Study

The toxic and unhealthy effects of Barbecue (BBQ) smoke is well known. Incomplete combustion of energy sources such as charcoal and wood chips give rise to Volatile Organic Compounds (VOCs) such as toluene and formaldehyde. They also give rise to particulate matter of small caliber e.g. PM25 that readily enter the pulmonary system. The net effect is a substantial risk of pulmonary diseases and possible carcinogenic effects. However, little progress has been made in terms of finding a way to cleanse the smoke of these potential hazards while at the same time preserving the ingredients of BBQ that prompt its use in the first place. Syringol and Guaiacol are two VOCs that provide the desirable smell and taste for the BBQ user. Here we review the progress to date of the steps that have been taken to solve this health concern and then propose a novel plan to execute differential scrubbing of BBQ smoke. It is suggested that activated carbon will preferentially adsorb more of the main body of VOCs than Syringol and Guaiacol simply because the latter two compounds are phenols which happen to be polar molecules. Activated carbon used for scrubbers is non-polar and tends to adsorb non-polar VOCs rather than polar VOCs. A pilot experiment was performed to exhibit the predicted differential adsorption. Smoke generated from an ordinary BBQ grill was allowed to be scrubbed by a high concentration that removed all VOCs including Syringol. The Syringol was monitored indirectly by an olfaction test. A 50% reduction in carbon concentration resulted in a dramatic differential reduction of the VOCs with a much greater adsorption of overall VOCs in comparison to Syringol. The results are encouraging in that this differential adsorption process does provide a potential to rid much of the toxic VOCs from common BBQ practice. Future studies are suggested including the design of a carbon scrubber system for the common BBQ grill.

Development of nitrogen-rich hierarchical porous carbon for high selective adsorption of methanol in multi-VOCs waste gas recovery processes

Methanol is a typical polar volatile organic compound that has been commonly used as a solvent in industrial processes and is considered as an important resource. It often appears with aromatic compounds in practical application scenarios. Conducting methanol and aromatic compounds recycle technology can provide us with a sustainable carbon source for fuels and materials well beyond the fleeting fossil fuel era. Post-synthesis modification (PSM) has been utilized to incorporate 3-amino-1,2,4-triazole (Atz) into ZIF-8, thereby enabling the derivation of mesopore structure and enhancement of nitrogen content in ZIF-8 derived carbon. With this method the obtained carbon exhibited a highly polarizable micro-mesoporous structure, resulting in high adsorption capacity for methanol adsorption at low concentrations. The experimental results showed that the VOCs adsorption on porous carbon is primarily dictated by its microporous structure at high pressure, and predominantly governed by the presence of nitrogen functional groups and the micro-mesoporous properties at low pressure. DFT theoretical analysis also showed that nitrogen functional group can improve the absorption capacity of methanol by adsorbents through changing the electron distribution and surface polarity of carbon-based materials. Finally, based on the emission properties that is low concentration and high volume of VOCs waste gas in industrial application, ZIF8-24-700 and BACs-36 materials (Wang et al., 2023) were used to further prove the feasibility of this technology under low VOCs concentration, which achieve recovery rates of 99 % for toluene and 95 % for methanol, respectively.

A Versatile Shaping Method of Very-High Loading Porous Solids Paper Adsorbent Composites.

Owing to their high porosity and tunability, porous solids such as metal-organic frameworks (MOFs), zeolites, or activated carbons (ACs) are of great interest in the fields of air purification, gas separation, and catalysis, among others. Nonetheless, these materials are usually synthetized as powders and need to be shaped in a more practical way that does not modify their intrinsic property (i.e., porosity). Elaborating porous, freestanding and flexible sheets is a relevant shaping strategy. However, when high loadings (>70wt.%) are achieved the mechanical properties are challenged. A new straightforward and green method involving the combination softwood bleached kraft pulp fibers (S) and nano-fibrillated cellulose (NFC) is reported, where S provides flexibility while NFC acts as a micro-structuring and mechanical reinforcement agent to form high loadings porous solids paper sheets (>70wt.%). The composite has unobstructed porosity and good mechanical strength. The sheets prepared with various fillers (MOFs, ACs, and zeolites) can be rolled, handled, and adapted to different uses, such as air purification. As an example of potential application, a MOF paper composite has been considered for the capture of polar volatile organic compounds exhibiting better performance than beads and granules.

Drastically boosting acetone capture by O/N co-doped Enteromorpha porous carbon: Key role of optimizing pore structure and improving surface polarity

Porous carbon exhibits great potential for removing volatile organic compounds (VOCs) due to its high specific surface and rich porous structure. However, the nonpolar surface of porous carbon leads to its unsatisfactory adsorption of polar VOCs. Here, the Enteromorpha-based O/N co-doped porous carbon (EONC) material was prepared using a two-step pyrolytic activation, including pre-carbonization with urea to improve the surface polarity, followed by KOH activation to optimize the pore structure. The EONC has a high specific surface (3026 m2/g), chemical compositions (9.8% N and 15.5% O), and ID/IG ratio (0.963). The results reveal that the adsorption capacity of EONC for acetone could reach up to 461.7 mg/g at appropriate reaction conditions. The adsorption mechanism of EONC for acetone is mainly attributed to the polar interaction forces of acetone by abundant O/N functional groups on the surface and the ultrahigh specific surface area derived from the rich two-dimensional pore structures. Combined with correlation analysis and theoretical calculations, we found that compared to other O/N functional groups, the carbonyl (–CO) and pyrrolic-N are more beneficial for the capture of acetone. Therefore, EONC, with excellent pore structure and appropriate surface polarity, is a promising material for removing polar VOCs in practical applications.

Hierarchical porous carbon with tunable apertures and nitrogen/oxygen heteroatoms for efficient adsorption and separation of VOCs

Porous carbon materials are good adsorbent candidates for removing volatile organic compounds (VOCs) due to their reliability and cost-effectiveness. Especially, the pore size distribution (PSD) of porous carbon materials plays a critical role in VOCs adsorption and separation. In this study, we present benzimidazole-derived porous carbons (BICs) with controllable pore size and oxygen/nitrogen heteroatoms. The pore size is controlled by adjusting the reaction degree of inorganic salt (K2CO3) and nitrogen-containing groups in the system. The tunable pore size distribution makes BICs highly efficient for the adsorption and separation of VOCs. BIC-3-900 exhibits a dominant pore size distribution of 3.0–4.0 nm and an exceptionally high total pore volume of 2.42 cm3/g, leading to ultra-high adsorption capacities for benzene and methanol (22.19 and 52.65 mmol/g, respectively) at 293 K. In addition, BIC-1-700 dominated by the micropore size is more favorable for adsorbing low-concentration small molecule VOCs (with a dynamic adsorption capacity of 4.21 mmol/g for methanol at 3800 ppm). In terms of the adsorptive separation performance, BIC-1-900 has an efficient benzene/methanol selectivity (∼30.13) due to its PSD (1.2–2.0 nm) which was more favorable for capturing low-concentration benzene. Moreover, both experimental and simulation (GCMC and DFT) results demonstrate that the abundant N/O heteroatoms doping in BIC-1-700 results in charge heterogeneity and stronger electrostatic affinity for polar VOCs molecules. Herein, our findings suggest that BICs with controllable pore size and oxygen/nitrogen heteroatoms have significant potential in practical VOCs capture and separation.

Activated carbon modified with polyethyleneimine and MgO: Better adsorption of aldehyde and production of regenerative VOC adsorbent using a photocatalyst

In this study, a renewable adsorbent containing a photocatalyst is developed that exhibits effective adsorption performance for polar volatile organic compounds (VOCs) that are not well adsorbed by activated carbon (AC). AC is used as the basic adsorbent, and the surface of the AC is modified with polyethyleneimine (PEI) and magnesium oxide (MgO) for the effective adsorption of polar VOCs. In addition, a renewable VOC adsorbent and filter are demonstrated by introducing titanium dioxide (TiO2) as a photocatalyst to impart regeneration. The changes in the physical and chemical structures of the AC surface due to the modification with PEI and the loading of MgO and its effects are confirmed through scanning electron microscopy, Brunauer–Emmett–Teller (BET) analysis, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy analyses. Developing slit pores containing polar functional groups on the AC through PEI deposition and loading MgO in the pore of AC increase the adsorption capacity of acetaldehyde by four times (3.08–13.8 mg g−1). In addition, PEI deposition shows high regeneration efficiency (86.4 %) with the application of TiO2. This study provides important insights into the development of renewable VOC filters that can be used for various VOCs.

Design and Fabrication of Ultrathin Nanoporous Donor-Acceptor Copolymer-Based Organic Field-Effect Transistors for Enhanced VOC Sensing Performance.

The development of organic field-effect transistor (OFET) chemical sensors with high sensing performance and good air stability has remained a persistent challenge, thereby hindering their practical application. Herein, an OFET sensor based on a donor-acceptor copolymer is shown to provide high responsivity, sensitivity, and selectivity toward polar volatile organic compounds, as well as good air stability. In detail, a polymer blend of N-alkyl-diketopyrrolo-pyrrole-dithienylthieno[3,2-b]thiophene (DPP-DTT) and polystyrene is coated onto an FET substrate via shearing-assisted phase separation (SAPS) combined with selective solvent etching to fabricate the DPP-DTT-based OFET device having an ultrathin nanoporous structure suitable for gas sensing applications. This is achieved via optimization of the film morphology by varying the shear rate to adjust the dynamic balance between the shear and capillary forces to obtain an ultrathin thickness (∼8 nm) and nanopore size (80 nm) that are favorable for the efficient diffusion and interaction of analytes with the active layer. In particular, the sensor presents high responsivities toward methanol (∼70%), acetone (∼51.3%), ethanol (∼39%), and isopropyl alcohol (IPA) (∼29.8%), along with fast response and recovery times of ∼80 and 234 s, respectively. Moreover, the average sensitivity was determined to be 5.75%/ppm from the linear plot of the responsivity against the methanol concentration in the range of 1-100 ppm. Importantly, the device also exhibits excellent long-term (30-day) air and thermal storage stability, thereby demonstrating its high potential for practical applications.

In Operando Spectroscopic Ellipsometry Investigation of MOF Thin Films for the Selective Capture of Acetic Acid.

The emission of polar volatile organic compounds (VOCs) is a major worldwide concern of air quality and equally impacts the preservation of cultural heritage (CH). The challenge is to design highly efficient adsorbents able to selectively capture traces of VOCs such as acetic acid (AA) in the presence of relative humidity (RH) normally found at storage in museums (40-80%). Although the selective capture of VOCs over water is still challenging, metal-organic frameworks (MOFs) possess highly tunable features (Lewis, Bronsted, or redox metal sites, functional groups, hydrophobicity, etc.) suitable to selectively capture a large variety of VOCs. In this context, we have explored the adsorption efficiency of a series of MOFs thin films (ZIF-8(Zn), MIL-101(Cr), and UiO-66(Zr)-2CF3) for the selective capture of AA based on a UV/vis and FT-IR spectroscopic ellipsometry in operando study (2-6% of relative pressure of AA under 40% of RH), namely conditions close to the realistic environmental storage conditions of cultural artifacts. For that purpose, optical quality thin films of MOFs were prepared by dip-coating, and their AA adsorption capacity and selectivity were evaluated under humid conditions by measuring the variation of the refractive index as a function of the vapor pressures while the chemical nature of the coadsorbed analytes (water and AA) was identified by FT-IR ellipsometry. While thin films of ZIF-8(Zn) strongly degraded upon exposure to AA/water vapors, films of MIL-101(Cr) and UiO-66(Zr)-2CF3 present a high chemical stability under those conditions. It was shown that MIL-101(Cr) presents a high AA adsorption capacity due to its high pore volume but exhibits a poor AA adsorption selectivity under humid conditions. In contrast, UiO-66(Zr)-2CF3 was shown to overpass MIL-101(Cr) in terms of AA/H2O adsorption selectivity and AA adsorption/desorption cycling stability because of its high hydrophobic character, suitable pore size for adequate confinement, and specific interactions.

Room Temperature Humidity Tolerant Xylene Sensor Using a Sn-SnO2 Nanocomposite

Xylene is one of the representative indoor pollutants, even in ppb levels, that affect human health directly. Due to the non-polar and less reactive nature of xylene, its room temperature detection is challenging. This work demonstrates a metallic tin-doped Sn-SnO2 nanocomposite under controlled pH conditions via a simple solvothermal route. The Sn nanoparticles are uniformly distributed inside the SnO2 nanospheres of ∼70 nm with a high specific surface area of 118.8 m2/g. The surface of the Sn-SnO2 nanocomposite exhibits strong affinity toward benzene, toluene, ethylbenzene, and xylene (BTEX) compared to other polar volatile organic compounds (VOCs) such as ethanol, acetone, isopropyl alcohol, formaldehyde, and chloroform tested in this study. The sensor's response is highest for xylene among BTEX molecules. Under ambient room temperature conditions, the sensor exhibits a linear response to xylene in the 1-100 ppm range with a sensitivity of ∼255% at 60 ppm within ∼1.5 s and recovers in ∼40 s. The sensor is hardly affected by humidity variations (40-70%), leading to enhanced reliability and repeatability under dynamic environmental conditions. The meso and microporous nanosphere morphology act as a nanocontainer for non-polar VOCs to diffuse inside the nanostructures, providing easy accessibility. The metallic Sn increases the affinity for less reactive xylene at room temperature. Thus, the nanocatalytic Sn-SnO2 nanocomposite is an active gas/VOC sensing material and provides an effective solution for sensing major indoor pollutants under humid conditions.

Textile-Based Volatile Organic Compound Sensors Using Cellulose Fabrics and Direct Dyes

ABSTRACT In order to fabricate colorimetric textile sensors detecting gas phase of volatile organic compounds (VOCs), 11 kinds of direct dyes were investigated for 13 types of VOCs. Direct Violet 51 was chosen for its best sensing performance both instrumentally and visibly. Direct Violet 51 exhibited the change of color strength and color hue by exposure VOCs. The dyed cotton fabrics detected polar VOCs well, especially N,N-dimethylformamide (DMF). The colorimetric cotton-based textile sensor dyed with Direct Violet 51 exhibited approximately 10 of color difference (ΔE) under 10 ppm DMF gas within 100 min, and the maximum absorption wavelength was shifted from 560 nm to 530 nm. The sensing mechanisms could be summarized in three factors: solvatochromism and aggregative characteristics from the point of view of dye, and adsorption amount of VOCs for fabric. The colorimetric textile sensor retained its sensing performance after 10 cycle tests.

Hydrophobic MOFs for the efficient capture of highly polar volatile organic compound

Effective capture of polar volatile organic compounds under environmental conditions is a challenge owing to the adsorption competition between polar volatile organic compounds and water.

MOFs with Open Metal(III) Sites for the Environmental Capture of Polar Volatile Organic Compounds.

Metal-Organic Frameworks (MOFs) with open metal sites (OMS) interact strongly with a range of polar gases/vapors. However, under ambient conditions, their selective adsorption is generally impaired due to a high OMS affinity to water. This led previously to the privilege selection of hydrophobic MOFs for the selective capture/detection of volatile organic compounds (VOCs). Herein, we show that this paradigm is challenged by metal(III) polycarboxylates MOFs, bearing a high concentration of OMS, as MIL-100(Fe), enabling the selective capture of polar VOCs even in the presence of water. With experimental and computational tools, including single-component gravimetric and dynamic mixture adsorption measurements, in situ infrared (IR) spectroscopy and Density Functional Theory calculations we reveal that this adsorption mechanism involves a direct coordination of the VOC on the OMS, associated with an interaction energy that exceeds that of water. Hence, MOFs with OMS are demonstrated to be of interest for air purification purposes.

MOFs with Open Metal(III) Sites for the Environmental Capture of Polar Volatile Organic Compounds

AbstractMetal–Organic Frameworks (MOFs) with open metal sites (OMS) interact strongly with a range of polar gases/vapors. However, under ambient conditions, their selective adsorption is generally impaired due to a high OMS affinity to water. This led previously to the privilege selection of hydrophobic MOFs for the selective capture/detection of volatile organic compounds (VOCs). Herein, we show that this paradigm is challenged by metal(III) polycarboxylates MOFs, bearing a high concentration of OMS, as MIL‐100(Fe), enabling the selective capture of polar VOCs even in the presence of water. With experimental and computational tools, including single‐component gravimetric and dynamic mixture adsorption measurements, in situ infrared (IR) spectroscopy and Density Functional Theory calculations we reveal that this adsorption mechanism involves a direct coordination of the VOC on the OMS, associated with an interaction energy that exceeds that of water. Hence, MOFs with OMS are demonstrated to be of interest for air purification purposes.

MOF/MWCNT-Nanocomposite Manipulates High Selectivity to Gas via Different Adsorption Sites with Varying Electron Affinity: A Study in Methane Detection in Parts-per-Billion.

Metal-organic frameworks (MOFs) present specific adsorption sites with varying electron affinity which are uniquely conducive to selective gas sensing but are typically large-band-gap insulators. On the contrary, multiwall carbon nanotubes (MWCNTs) exhibit superior mesoscopic transport exploiting strong electron correlations among sub-bands below and above the Fermi level at room temperature. We synergize them in a new class of nanocomposites based on zeolitic imidazolate framework-8 (ZIF-8) and report selective sensing of CH4 in ∼10 parts-per-billion (ppb) with a determined limit of detection of ∼0.22 ppb, hitherto unprecedented. The observed selectivity to CH4 over non-polar CO2, polar volatile organic compounds, and moisture has roots in competing electron-sharing mechanisms at its different adsorption sites. This important result provides a significant reference to guide future MOF-related composite research to achieve the best sensing performance. On molecular adsorption, MWCNTs facilitate electrical transport via manipulating the ZIF-8 band gap to show a p-type semiconductor behavior with lower activation energy to induce a measurable resistance change. Excellent repeatability and reversibility are shown. A carbon-engineered MOF composite has the potential to actuate similar selective response to low reactive gases via carrier manipulation in the energy band gap.

Hollow nano-CaCO3's VOC sensing properties: A DFT calculation and experimental assessments

Air is the most critical and necessary for life, and air quality significantly impacts people's health. Both indoor and outdoor pollution frequently contain volatile organic compounds (VOCs). Such contaminants provide immediate or long-term health risks to the living system. The present study investigates sorption characteristics of VOCs on hollow nano calcite (CaCO3) particles with 250 nm and 40 nm pore sizes to remove from the air ambient using the quartz crystal microbalance (QCM) technique at room temperature both experimentally and theoretically. The results were supported by density functional theory (DFT), and adsorption-desorption characteristics were studied with Langmuir adsorption isotherms. The QCM measurements showed a stable signal without having hysteresis, and the response of polar VOCs on hollow nano-CaCO3 particles such as ethanol, propanol, and humidity with higher polarity was less compared to solvents such as chloroform and dichloromethane, which revealed that the surfaces of CaCO3 particles have mostly non-polar properties. CaCO3 surface and VOC molecule interactions overlap with the Langmuir model. With DFT calculations, VOC and water molecule adsorption changes the CaCO3 Egap. Our findings show that the ΔEgap values increase as chloroform > dichloromethane > propanol > ethanol > water. This order suggests that the sensing response of the hollow CaCO3 structure is linearly proportional to the adsorption energies of VOC and water. The linear adsorption characteristics, high sensing response, and short recovery time illustrated that the newly synthesized nano-CaCO3 could be implemented as a new VOC adsorbent material for health, environmental sustainability, and in vitro microbiome cultures.

A case study on microwave pyrolysis of waste tyres and cocoa pod husk; effect on quantity and quality of utilizable products

Disposal of huge amounts of diverse wastes for reduced costs accompanied with gaining of energy and valuable chemicals is an eager topic in waste-to-energy and fuel business. Microwave pyrolysis is a thermochemical route providing such benefits. Waste scrap tyres (ST) and cocoa pod husk (CPH) as polymer and biomass representatives were pyrolyzed in microwave reactor at 440 W power for 30 min. Quantity and quality of pyrolysis products (gas, oil, and carbon black) were investigated. It was revealed, while set microwave pyrolysis conditions are sufficient for maximum decomposition of ST to pyrolysis products, it is necessary to optimize them for CPH. The gas produced by microwave pyrolysis of ST contains more H2 and CH4 than from conventional pyrolysis, thus, microwave pyrolysis is an effective tool for production of a fuel gas. The oil obtained by ST microwave pyrolysis is a complex mixture of mostly nonpolar aromatic compounds (toluene, benzene, limonene, styrene, o-xylene), while the oil obtained by CPH microwave pyrolysis contains mainly p-cresol, phenol and its derivatives. The ST-derived carbon black shows a well-established large-volume mesoporous-macroporous structure. The CPH-derived carbon black is a low-volume macroporous material with very well-developed microporosity. A higher gross calorific value of microwave ST-derived carbon black in comparison to conventionally prepared one is caused by its higher graphitization rate. Since the surface of ST-derived carbon black is more polar than CPH-derived one and with respect to chemical purity, it could be more suitable adsorbent for polar volatile organic compounds from gaseous emissions. It is necessary to develop a microporosity in ST-derived carbon black.

Preparation of conjugated polymer/reduced graphene oxide nanocomposites for high-performance volatile organic compound sensors

We have reported a facile approach to fabricate poly(3-hexylthiophene)/reduced graphene oxide (P3HT/rGO) composite films via the photoirradiation of the corresponding composite solutions. The films are applied to organic field-effect transistor (OFET) sensors for the high-performance detection of volatile organic compounds (VOCs). The photoirradiation of the composite solutions and the presence of rGO act synergistically to facilitate the molecular ordering of P3HT. Thus, the P3HT/rGO composite films containing 20 wt% rGO exhibit a maximized charge carrier mobility of ~0.18 cm2 V−1 s−1, which is 6-folds higher than that of pristine P3HT films. The interfacial interactions between rGO and P3HT are enhanced by the favorable π − π and electrostatic interactions following photoirradiation. The OFET sensors based on the P3HT/rGO composites consistently show enhanced sensitivity to polar VOCs (methanol, acetone, ethanol, and isopropyl alcohol) compared to those based on the pristine P3HT, photoirradiated bare P3HT, and pristine P3HT/rGO composites. In particular, the photoirradiated P3HT/rGO-based OFET sensors achieve significantly improved responsivity (~110.6%) to methanol vapors (10 ppm) under rapid on/off pulses of 60 s, compared to those based on pristine P3HT (~6.8%), photoirradiated bare P3HT (~20.8%), and pristine P3HT/rGO (~55.1%) composites. Finally, excellent response and recovery behaviors (e.g., ~15 s and ~42 s, respectively) are also observed.

Method for Accurate Quantitation of Volatile Organic Compounds in Urine Using Point of Collection Internal Standard Addition.

A method to achieve accurate measurement of unmetabolized volatile organic compounds (VOCs) in urine was developed and characterized. The method incorporates a novel preanalytical approach of adding isotopically labeled internal standard (ISTD) analogues directly to the collection container at the point of collection to compensate for analyte loss to the headspace and the collection container surfaces. Using this approach, 45 toxic VOCs ranging in water solubility and boiling point were evaluated and analyzed by headspace solid-phase microextraction/gas chromatography–mass spectrometry. Results show that urine VOCs could be equally lost to the container headspace as to the container surface suggesting similarity of these two regions as partition phases. Surface adsorption loss was found to trend with compound water solubility. In particular, with no headspace, more nonpolar VOCs experienced substantial losses (e.g., 48% for hexane) in a standard 120 mL urine cup at concentrations in the low- and sub-ppb range. The most polar VOCs evaluated (e.g., tetrahydrofuran) showed no significant loss. Other commonly practiced methods for urine sample collection and analysis such as aliquoting, specimen freezing, and use of surrogate ISTD were found to significantly bias results. With this method, we achieved errors ranging from −8.0 to 4.8% of spiked urine specimens. Paired urine and blood specimens from cigarette smokers were compared to assess this method.

Constructing a Resistive Gas Sensor Based on the Highly Stable Mil-53(Fe)/Ag/CNT Ternary Nanocomposite for Sensing Polar Volatile Organic Compounds Such as Methanol

In this study, MIL-53(Fe) nano-sized crystals were synthesized under microwave irradiation with various powers (80, 100 W) and ‎times (5, 10 min). Then, the crystals that had the best porous ‎structure were selected to prepare the MIL-53(Fe)/Ag/CNT ternary nanocomposite. Nano-sized crystals were characterized by scanning electron microscopy, Fourier transform infrared ‎spectroscopy, X-ray diffraction, and specific surface area analysis. Prepared nanocomposite was used to fabricate a resistive gas sensor device for detecting volatile organic compounds in environmental conditions (10% relative humidity and 25°C). The resistive gas sensor showed higher response to volatile organic compounds with higher polarity such as methanol. The lowest detectable concentration of methanol was 1.2 ppm. Linearity of the calibration curve was obtained in a wide range from 0 to 30 mg/L.