Tuning the metal-support interactions in titanium dioxide-supported palladium photocatalysts against toluene in air.

The activity of supported noble metal (e.g., palladium (Pd)) catalysts is often governed by the combined effects of multiple factors (e.g., electronic and geometric properties of the support, surface chemistry of metal nanoparticles (NPs), and metal-support interactions). Pd/titanium dioxide (TiO2) catalyst has been developed as a highly efficient photocatalytic degradation (PCD) system against gaseous toluene based on high-temperature pretreatment (300 and 450 °C) in a mixed stream of hydrogen (H2) and (N2). The interaction of Pd NPs with TiO2 synergistically improves the PCD efficiency of toluene through the efficient adsorption and activation of toluene as well as molecular oxygen (O2) and water (H2O) for the facile generation of reactive oxygen species (ROS (e.g., superoxide anion (•O2-) and hydroxyl (•OH) radicals)). The PCD efficiency of the prepared sample against 5 ppm toluene (at 20% relative humidity (RH)) is 79.6% with the values of maximum reaction rate, quantum yield, space-time yield, and clean air delivery rate as 9.9 µmol g-1 h-1, 1.68E-03 molecules photon-1, 1.68E-02 molecules photon-1 g-1, and 4.8 L h-1, respectively. Based on this research, the PCD mechanism of gaseous toluene has been explored along with the dynamic behavior of O2 and H2O for ROS generation and their relative contribution to the PCD of toluene. As such, this research offers a perspective for designing advanced photocatalysts through surface defect engineering.

Removal of gaseous benzene by a fixed-bed system packed with a highly porous metal-organic framework (MOF-199) coated glass beads.

The utility of nanomaterial adsorbents is often limited by their physical features, especially fine particle size. For example, a large bed-pressure drop is accompnied inevitably, if fine-particle sorbents are used in a packed bed system. To learn more about the effect of adsorbent morphology on uptake performance, we examined the adsorption efficiency of metal-organic framework 199 (MOF-199) in the pristine (fine powder) form and after its binding on to glass beads as an inert support. Most importantly, we investigated the effect of such coatings on adsorption of gaseous benzene (0.1-10 Pa) in a dry N2 stream, particularly as a function of the amount of MOF-199 loaded on glass beads (MOF-199@GB) (i.e., 0,% 1%, 3%, 10%, and 20%, w/w) at near-ambient conditions (298 K and 1 atm). A 1% MOF-199 load gave optimal performance against a 0.1 Pa benzene vapor stream in 1 atm of N2, with a two-to five-fold improvement (e.g., in terms of 10% breakthrough volume [BTV] (46 L atm [g.MOF-199)-1], partition coefficient at 100% BTV (3 mol [kg.MOF-199]-1 Pa-1), and adsorption capacity at 100% BTV (20 mg [g.MOF-199]-1 (areal capacity: 8.8 × 10-7 mol m-2) compared with those of 3%, 10%, and 20% loading. The relative performance of benzene adsorption was closely associated with the content of MOF-199@GB (e.g., 1% > 3% > 10% > 20%) and the surface availability (m2 [g.MOF-199]-1) such as 291 > 221 > 198 > 181, respectively. This study offers new insights into the strategies needed to expand the utility of finely powdered MOFs in various environmental applications.

Evidence of inter-species swing adsorption between aromatic hydrocarbons.

In this research, the competitive adsorption characteristics between aromatic hydrocarbons were investigated. It is well-known that an industrial effluent may contain a mixture of pollutants. The composition of effluents is usually highly variable in nature to depend upon the feedstock. Hence, one of the pollutants that is present in larger amounts may have the potential to dominate the sorption processes. Although many studies have investigated the competitive adsorption of volatile organic compounds (VOCs) onto activated carbon (AC) in detail, little is known about how the overall process is influenced when a fresh incoming VOC molecule encounters a sorbent bed pre-loaded with other VOCs. Consequently, the objective of the present study was to investigate the stability of pre-adsorbed VOC molecules in the presence of other potentially competitive VOCs in the influent stream. In this regard, the sorbent bed of AC was first preloaded with benzene (50 ppm (0.16 mg L-1)) and subsequently challenged by either high purity nitrogen or a stream of xylene (at 10, 50, or 100 ppm (0.043, 0.22, or 0.43 mg L-1)). The desorption rate of preloaded benzene and uptake rate of challenger xylene were assessed simultaneously. The maximum desorption rates of benzene (Rb) against two challenge scenarios (e.g., 100 ppm (0.43 mg L-1) xylene and pure N2) were very different from each other, i.e., 663 vs. 257 g kg-1 h-1, and their final benzene recoveries were 84% and 42%, respectively. The initially high desorption rate for the former quickly decreased with decreasing benzene residual capacity (C, mg g-1). Interestingly, the adsorption capacity of xylene increased considerably after the preloading of benzene (relative to no preloading). As such, 10% breakthrough volumes (BTV10) of 100, 50, and 10 ppm (0.43, 0.22, and 0.043 mg L-1) xylene challenge scenarios increased significantly from 100 to 186, 43.4 to 694, and 600 to 1000 L atm g-1, respectively. The prevalent mechanisms were analyzed using density functional theory (DFT)-based modelling approaches. The results demonstrated effective replacement of pre-adsorbed molecules with weaker affinity (e.g., benzene) when challenged by molecules with stronger affinity (e.g., xylene) toward the sorbent; this was accompanied by noticeable synergistic enhancement in the adsorption capacity of the latter.

The effects of continuous- and stop-flow gas streams on adsorptive removal of benzene vapor using type - II covalent organic polymers.

Various materials have been investigated for the adsorptive removal of volatile organic compounds (VOCs, such as benzene). However, most materials proposed for the adsorptive removal of gaseous benzene (and other VOCs) perform relatively poorly (e.g., an impractically low-service 10% breakthrough volume [BTV10] at < 100 ppm). The adsorbent uptake rate (mg g-1 min-1) can also be assessed as a function of the gas-stream flow rate (or space velocity). The main aim of this study is to explore the effect of two different gas-stream supply modes - stopped flow (at a fixed stream flow rate of 330 mL atm min-1) vs. continuous flow (a variable-stream flow rate of 100, 200, or 330 mL atm min-1) on the adsorption metrics of gaseous benzene on 5 mg of two types of - II covalent organic polymers (COPs: CBAP-1 [DETA], CD; or CBAP-1 [EDA], CE). The sorbent tube outlet stream was sampled by two respective sampling methods (i.e., a large-volume injector [LVI] for stopped flow vs. syringe injection [SI] for continuous flow) for sample quantitation by gas chromatography flame-ionization detection (GC-FID). The observed BTV10 values in the two sampling modes were similar when tested using 10 ppm benzene, irrespective of sorbents: 56/60 (CD) vs. 620/624 L atm g-1 (CE). BTV10 values increased systematically with decreasing stream-flow rates to reflect the importance of space velocity in adsorptive removal of benzene. The overall assessment of adsorption performance between stopped flow (LVI) and continuous flow (SI) revealed that the performance of the adsorbent is independent of flow mode (e.g., when performance was compared at flow rate of 330 mL min-1).

The retrograde adsorption phenomenon at the onset of breakthrough and its quantitation: An experimental case study for gaseous toluene on activated carbon surface.

The adsorption dynamics of common solid sorbents against various pollutant species are yet poorly understood with respect to the retrograde phenomenon in which the relationship between breakthrough vs. pulled volume is characterized by an early unusual trend (initial increase followed by a decrease to a minimum) and by a normal trend of finally increasing to 100% (or equilibrium). If such trend is expressed in terms of the partition coefficient (PC), a reversed trend of adsorption processes becomes more evident. Retrograde has been previously observed in the initial breakthrough (<10%) isotherms in continuous flow gas-phase adsorption processes. However, retrograde has been neglected/overlooked and not discussed at all in the main stream literature even when it is explicitly observed from isotherm datasets. To properly describe the various aspects of such process, a stop-flow technique was developed to measure the adsorption isotherm of a model volatile organic compound (i.e., toluene in this study) onto a commercial low-cost sorbent (activated carbon: AC). Accordingly, a 10% breakthrough volume of 762 L atm g-1 (corresponding adsorption capacity of 142 mg g-1) was determined (at an inlet stream 5 Pa of toluene in 1 atm of N2 and 5 mg of AC). This automated method was effective to generate a detailed breakthrough profile at high stream-flow rates (or high space velocities) to specifically detect the retrograde phenomenon at the breakthrough onset. This study offers a practical approach towards establishing an in-depth monitoring protocol for the rare retrograde phenomenon.

A comparison of figure of merit (FOM) for various materials in adsorptive removal of benzene under ambient temperature and pressure.

To effectively remove gaseous pollutants from air using sorbents, a thorough knowledge of the actual sorption performance is needed at ambient conditions rather than at unrealistically high-pressure conditions, as is commonly presented in the literature. To this end, the sorbent capacities of gaseous benzene were evaluated at a constant sorbent bed inlet pressure (50 ppm or ~5 Pa) in 1 atm of N2, room temperature (298 K), a fixed flow rate (50 mL min-1), and equal outlet sampling intervals (5 min). The benzene adsorption patterns were investigated against six sorbent types in a total of 17 different forms: 1- zeolite in five forms: beads (ZB), ground to 212 µm (ZG212), beads ground to 300 µm (ZG300), coarsely ground/washed zeolite (ZWc), and coarsely ground/washed/thermally treated zeolite (ZTc), 2- activated carbon in two forms: 212 µm (ACd212) and granular (ACdg), 3- Carbopack-X (CX), 4- Tenax TA (TA), 5- used black tea leaves of 150 or 300 µm in three forms: dry (TD150/TD300), wet (TW150/TW300), and wet dust (TWd), and 6- used ground coffee in either dry (CD) or wet forms (CW). Accordingly, the largest adsorption capacities at 5 Pa (e.g., >10 mg g-1) were observed for ACd212 (79.1) and ACdg (73.6). Moderate values (e.g., 5 < < 10 mg g-1) were obtained for ZG212 (7.98), CX (6.79), ZG300 (5.70), and ZB (5.58), while the remainder were far lower at < 5 mg g-1 (e.g., tea leaves, ground coffee, TA, ZWc, and ZTc). The experimental benzene capacities of the tested sorbents were further assessed by the Langmuir, Henry's law, Freundlich, Dubinin-Radushkevich, and Elovich isotherm models. The linearized Langmuir adsorption isotherms of ACd212, ACdg, and CX showed the presence of more than one adsorption site (i.e., retrograde at the lowest pressures and two others at higher pressures). However, TA, zeolite, tea leaves, and ground coffee exhibited a type-V isotherm, wherein the sorption capacity continued to increase with loaded volume (i.e., multilayer adsorption). Thus, ACd212 has the best figure-of-merit based on a high 10% breakthrough volume (BTV) and low cost for real-world applications.

The effect of diverse metal oxides in graphene composites on the adsorption isotherm of gaseous benzene.

The effective removal technique is necessary for the real world treatment of a hazardous pollutant (e.g., gaseous benzene). In an effort to develop such technique, the adsorption efficiency of benzene in a nitrogen stream (5 Pa (50 ppm) at 50 mL atm min-1 flow rate and 298 K) was assessed against 10 different metal oxide/GO composite materials (i.e., 1: graphene oxide Co (GO-Co (OH)2), 2: graphene oxide Cu (GO-Cu(OH)2), 3: graphene oxide Mn (GO-MnO), 4: graphene oxide Ni (GO-Ni(OH)2), 5: graphene oxide Sn (GO-SnO2), 6: reduced graphene oxide Co (rGO-Co(OH)2), 7: reduced graphene oxide Cu (rGO-Cu(OH)2), 8: reduced graphene oxide Mn (rGO-MnO), 9: reduced graphene oxide Ni (rGO-Ni(OH)2), and 10: reduced graphene oxide Sn (rGO-SnO2)) in reference to their pristine forms of graphene oxide (GO) and reduced graphene oxide (rGO). The highest adsorption capacities (at 100% breakthrough) were observed as ~23 mg g-1 for both GO-Ni(OH)2 and rGO-SnO2, followed by GO (~19.1 mg g-1) and GO-Co(OH)2 (~18.8 mg g-1). Therefore, the GO-Ni(OH)2 and rGO-SnO2 composites exhibited considerably high capacities to treat streams containing >5 Pa of benzene. However, the lowest adsorption capacity was found for GO-MnO (0.05 mg g-1). Alternately, if expressed in terms of the 10% breakthrough volume (BTV), the five aforementioned materials showed values of 0.50, 0.46, 0.40, 0.44, and 0.39 L g-1, respectively. The experimental data of target sorbents were fitted to linearized Langmuir, Freundlich, Elovich, and Dubinin-Radushkevich isotherm models. Accordingly, the non-linear Langmuir isotherm model revealed the presence of two or more distinct sorption profiles for several of the tested sorbents. Most of the sorbents showed type-III isotherm profiles where the sorption capacity proportional to the loaded volume.

Competitive adsorption of gaseous aromatic hydrocarbons in a binary mixture on nanoporous covalent organic polymers at various partial pressures.

Covalent-organic polymers (COPs) are recognized for their great potential for treating diverse pollutants via adsorption. In this study, the sorption behavior of benzene and toluene was investigated both individually and in a binary mixture against two types of COPs possessing different -NH2 functionalities. Namely, the potential of COPs was tested against benzene and toluene in a low inlet partial pressure range (0.5-20 Pa) using carbonyl-incorporated aromatic polymer (CBAP)-1-based diethylenediamine (EDA) [CD] and ethylenetriamine (DETA) [CE]. The maximum adsorption capacity and breakthrough values of both COPs showed dynamic changes with increases in the partial pressures of benzene and toluene. The maximum adsorption capacities (Amax) of benzene (as the sole component in N2 under atmospheric conditions) on CD and CE were in the range of 24-36 and 33-75 mg g-1, respectively. In contrast, with benzene and toluene in a binary mixture, the benzene Amax decreased more than two-fold (range of 2.7-15 and 6-39 mg g-1, respectively) due to competition with toluene for sorption sites. In contrast, the toluene Amax values remained consistent, reflecting its competitive dominance over benzene. The adsorption behavior of the targeted compounds (i.e., benzene and toluene) was explained by fitting the adsorption data by diverse isotherm models (e.g., Langmuir, Freundlich, Elovich, and Dubinin-Radushkevich). The current research would be helpful for acquiring a better understanding of the factors affecting competitive adsorption between different VOCs in relation to a given sorbent and across varying partial pressures.

The unique features of non-competitive vs. competitive sorption: Tests against single volatile aromatic hydrocarbons and their quaternary mixtures.

The adsorption characteristics of four aromatic hydrocarbons (i.e., benzene, toluene, xylene, and styrene) onto ground-activated carbon were investigated both independently and as a mixture of the four at <10 Pa partial pressures (e.g., 0-100 ppm concentration range). The maximum sorption capacities for benzene, toluene, styrene, and xylene were measured both as a sole component and as a mixture (at 10 Pa). In the former, the values were approximately 123, 184, 272, and 238 mg g-1, respectively. In contrast, the latter values were 5, 52, 222, and 248 mg g-1 respectively, showing dramatic reduction in lighter compounds (below C7) relative to heavier ones (above C8). The mechanistic detail of sorption has been explained in terms of Henry's law and Langmuir, Freundlich, Dubinin-Radushkevich, and Elovich isotherm models. The linearized Langmuir adsorption isotherm analysis showed three sorption pressure regions: low (<1 Pa, retrograde), intermediate (1-4 Pa), and high (4-10 Pa). As such, the outcome of this study offers a unique opportunity to acquire detailed information on the dramatic and dynamic effects of the sorptive interaction between competing sorbates, along with a common sorption process between sorbent and sorbate at 298 K.

Utilization of activated carbon as an effective replacement for a commercialized three-bed sorbent (Carbopack) to quantitate aromatic hydrocarbons in ambient air.

The potential use of activated carbon (AC) as an inexpensive and effective alternative sorbent material in thermal desorption is presented and validated for the analysis of aromatic volatile organic compounds (VOCs) such as benzene, toluene, m-xylene, and styrene (BTXS) in air. The optimum desorption conditions of an AC sampling tube (2 mg AC bed) were determined and compared with a commercial three-bed (Carbopack; C + B + X) tube sampler as a reference. The AC sampler exhibited good linearity (R2 > 0.99) and reproducibility (RSE of 2.38 ±â€¯0.21%) for BTXS analysis. The AC tube sampler showed good storability (up to 3 d) and excellent recyclability (up to 50 cycles). An analysis of BTXS in ambient air showed excellent agreement between AC and CBX (bias < 5%). The 1% breakthrough volume values for 2 mg AC, when tested at 100 ppb of benzene as a sole component or in a BTXS mixture, were 10,000 or 5000 L g-1, respectively. The results of this study support the performance of AC as a suitable medium for sampling VOCs as reliable as high-cost commercial sorbent products.

The effect of flavor content in e-liquids on e-cigarette emissions of carbonyl compounds.

The effect of flavors on carbonyl compound (CC) emission factors (EF) from electronic cigarettes (ECs) vaping was investigated at the default vaping (voltage) setting in all experiments using a total of 21 lab-made e-liquid samples (five different types of retail flavorant bases: beverage/dessert/fruit/mint/tobacco). Each flavorant base was added to a separate unflavored base composed of a 1:1 mixture of propylene glycol/vegetable glycerol (PG/VG) at four levels (5/10/30/50% (v/v)). The e-liquid CC levels increased linearly with flavorant base content, 1.3-10.5 times (R2: 0.762-0.999). The vaping CC EFs increased linearly with flavorant base content (if ≥ 10%) from 1.0 to 92 times (R2: 0.431-0.998). For flavorant base content of 0%, 5%, and 10%, the EFs ranged from undetected to 0.11 µg puff-1 (acetone). The 40-year cancer risk due to formaldehyde (70 kg EC user inhaling 5% flavorant base content e-liquid: 120 puffs day-1) is estimated to be 2.0E-06 (highest) compared to 1.0E-06 for the 1:1 PG:VG base. Most formaldehyde vaped from the fruit flavored e-liquid was the flavorant base. The CC concentrations in EC liquids (before vaping) were approximately linear with e-liquid flavorant base content. Retail e-liquid product information labels should be guided to provide a complete list of all ingredients, their concentrations, and carbonyl compound EFs.

Airborne volatile aromatic hydrocarbons at an urban monitoring station in Korea from 2013 to 2015.

The concentrations of C6-C10 volatile aromatic hydrocarbons (AHCs) in air were measured at an urban air quality monitoring station in Jong-Ro, Seoul, Korea, between 2013 and 2015. Their temporal patterns (e.g., diurnal, intraweek, daily) were assessed individually and collectively as groups of benzene, toluene, ethylbenzene, styrene, and xylene (BTESX); total aliphatic hydrocarbon (TALHC: C2-C12); total aromatic hydrocarbon (TARHC: C6-C10); and total hydrocarbon (THC: C2-C12). The highest mean AHC concentrations over the 3-year study (in ppb (v/v)) were observed for toluene (6.0 ±â€¯4.3), followed by the xylenes (1.5 ±â€¯1.3), ethylbenzene (0.85 ±â€¯0.93), benzene (0.73 ±â€¯0.77), and styrene (0.16 ±â€¯0.30) nL/L. The mean ppbC ((v/v), nL∙atm∙C/nL∙atm) values for BTESX, TALHC, TARHC, and THC were 65.8, 113, 77.7, and 191 ppbC, respectively. For most AHC species (e.g., toluene, styrene, and BTESX), only weak seasonal trends were observed in contrast to temporally varying species like nitric oxide (NO) (e.g., 26.3 ppb (January-February) vs. 8.5 ppb (July-August) during weekdays in 2013). Furthermore, toluene and NO concentrations were much higher (up to a factor 3) on weekdays than on Sunday for most weeks. This might reflect reduced anthropogenic activities on Sunday.

Determination of carbonyl compounds in electronic cigarette refill solutions and aerosols through liquid-phase dinitrophenyl hydrazine derivatization.

In this study, we report a 2,4-dinitrophenylhydrazine (DNPH) derivatization HPLC/UV method to quantify carbonyl compounds (CCs) either in electronic cigarette (EC) refill solutions or in vaped aerosols. Vaped aerosol samples were entrained in a 1 L atm min-1 ambient lab air stream and pulled through an impinger containing a DNPH solution for derivatization. The mass change tracking (MCT) approach was used to check mass balance. Refill solution samples were diluted (2, 4, and 10 times) in a DNPH/acetonitrile solution for derivatization. EC vaping samples were collected for 5, 10, or 15 puffs (2-s puff duration) with a 10-s interpuff interval. The DNPH derivatization method was used successfully for the estimation of both EC liquid CCs concentrations and vaping emission factors. The results for formaldehyde (FA), acetaldehyde (AA), and butyraldehyde (BA) were determined as 10.4 ± 3.10 µg mL-1 (27.6 ± 7.43 ng puff-1), 1.9 ± 0.83 µg mL-1 (4.4 ± 1.98 ng puff-1), and 4.4 ± 2.82 µg mL-1 (12.0 ± 7.43 ng puff-1), respectively.

The micro-environmental impact of volatile organic compound emissions from large-scale assemblies of people in a confined space.

Large-scale assemblies of people in a confined space can exert significant impacts on the local air chemistry due to human emissions of volatile organics. Variations of air-quality in such small scale can be studied by quantifying fingerprint volatile organic compounds (VOCs) such as acetone, toluene, and isoprene produced during concerts, movie screenings, and sport events (like the Olympics and the World Cup). This review summarizes the extent of VOC accumulation resulting from a large population in a confined area or in a small open area during sporting and other recreational activities. Apart from VOCs emitted directly from human bodies (e.g., perspiration and exhaled breath), those released indirectly from other related sources (e.g., smoking, waste disposal, discharge of food-waste, and use of personal-care products) are also discussed. Although direct and indirect emissions of VOCs from human may constitute <1% of the global atmospheric VOCs budget, unique spatiotemporal variations in VOCs species within a confined space can have unforeseen impacts on the local atmosphere to lead to acute human exposure to harmful pollutants.

Insights into the adsorption capacity and breakthrough properties of a synthetic zeolite against a mixture of various sulfur species at low ppb levels.

The sorptive removal properties of a synthetic A4 zeolite were evaluated against sulfur dioxide (SO2) and four reference reduced sulfur compounds (RSC: hydrogen sulfide (H2S), methanethiol (CH3SH), dimethyl sulfide (DMS, (CH3)2S), and dimethyl disulfide (DMDS, CH3SSCH3). To this end, a sorbent bed of untreated (as-received) A4 zeolite was loaded with gaseous standards at four concentration levels (10-100 part-per-billion (ppb (v/v)) at four different volumes (0.1, 0.2, 0.5, and 1 L increments) in both increasing (IO: 0.1-1.0 L) and decreasing volume order (DO: 1.0 to 0.1 L). Morphological properties were characterized by PXRD, FTIR, and BET analysis. The removal efficiency of SO2 decreased from 100% for all concentrations at 0.1 L (initial sample volume) to ∼82% (100 ppb) or ∼96% (10 ppb) at 3.6 L. In contrast, removal efficiency of RSC was near 100% at small loading volumes but then fell sharply, irrespective of concentration (10-100 ppb) (e.g., 32% (DMS) to 52% (H2S) at 100 ppb). The adsorption capacity of zeolite, if expressed in terms of solid-gas partition coefficient (e.g., similar to the Henry's law constant (mmol kg(-1) Pa(-1))), showed moderate variabilities with the standard concentration levels and S compound types such as the minimum of 2.03 for CH3SH (at 20 ppb) to the maximum of 13.9 for SO2 (at 10 ppb). It clearly demonstrated a notable distinction in the removal efficiency of A4 zeolite among the different S species in a mixture with enhanced removal efficiency of SO2 compared to the RSCs.

A review on the role of organic inputs in maintaining the soil carbon pool of the terrestrial ecosystem.

Among the numerous sources of greenhouse gases, emissions of CO2 are considerably affected by changes in the extent and type of land use, e.g., intensive agriculture, deforestation, urbanization, soil erosion, or wetland drainage. As a feasible option to control emissions from the terrestrial ecosystems, the scientific community has explored the possibility of enhancing soil carbon (C) storage capacity. Thus, restoration of damaged lands through conservation tillage, crop rotation, cover cropping, reforestation, sub-soiling of compacted lands, sustainable water management practices, and organic manuring are the major antidotes against attenuation of soil organic C (SOC) stocks. In this research, we focused on the effect of various man-made activities on soil biotic organics (e.g., green-, farm-yard manure, and composts) to understand how C fluxes from various sources contribute to the establishment of a new equilibrium in the terrestrial ecosystems. Although such inputs substitute a portion of chemical fertilizers, they all undergo activities that augment the rate and extent of decay to deplete the SOC bank. Here, we provide perspectives on the balancing factors that control the mineralization rate of organic matter. Our arguments are placed in the background of different land use types and their impacts on forests, agriculture, urbanization, soil erosion, and wetland destruction.

Development of the detection threshold concept from a close look at sorption occurrence inside a glass vial based on the in-vial vaporization of semivolatile fatty acids.

Headspace (HS) analysis has been recommended as one of the most optimal methods for extracting and analyzing volatile organic compounds from samples in diverse media such as soil and water. Short-chain volatile fatty acids (VFA, C3-C7) with strong adsorptivity were selected as the target compounds to assess the basic characteristics of the HS analysis through simulation of HS conditions by in-vial vaporization of liquid-phase standards (VL) in 25 mL glass vials. The reliability of the VL approach was assessed by apportioning the in-vial VFA mass into three classes: (1) vaporized fraction, (2) dynamic adsorption on the vial walls (intermediate stage between vaporization and irreversible absorption), and (3) irreversible absorptive loss (on the vial wall). The dynamic adsorption partitioning inside the vial increased with n-VFA carbon number, e.g., 43% (C2: acetic acid, extrapolated value), 65% (C3: propanoic acid), and 98% (C7: heptanoic acid). The maximum irreversible losses for the studied n-VFAs exhibited a quadratic relationship with carbon number. If the detection threshold limit (DTL: the onset of mass detection after attaining the maximum irreversible loss) is estimated, the DTL values for target VFAs were in the range of 101 ng for i-valeric acid to 616 ng for propionic acid, which are larger than the method detection limit by about 3 orders of magnitude. Consequently, quantitation of VFAs using the VL approach should be critically assessed by simultaneously considering the DTL criterion and the initial VFA masses loaded into the vial.

Efficient injection of low-mass ions into high magnetic field Fourier transform ion cyclotron resonance mass spectrometers.

RATIONALE: Low-mass cut-off restrictions for injecting ions from external ion sources into high magnetic fields impose limitations for wide mass range analyses with Fourier transform ion cyclotron resonance (FTICR) instruments. Radio-frequency (RF)-only quadrupole ion guides (QIGs) with higher frequencies can be used to overcome low-mass cut-off in FTICR instruments. METHODS: RF signals (1.0 MHz to 10.0 MHz) were applied to QIGs to transfer externally generated ions from either electron ionization (EI) or electrospray ionization (ESI) sources into ICR cells of 9.4 T FTICR mass spectrometers. Efficiencies of QIGs were evaluated using externally generated ions from: EI of acetone, air, and perfluorotributylamine mixture, EI of gas chromatography (GC)-separated components of a standard sample mixture, and ESI of complex mixtures such as petroleum and fulvic acid samples. RESULTS: We were able to transfer ions with m/z as low as 26 from an external EI source into the ICR cell of a 9.4 T FTICR mass spectrometer and extend the operational low-mass range for ESI-FTICR analyses. High mass resolving power and mass measurement accuracy of GC/FTICR mass spectrometry were utilized to discriminate between oxygenated and non-oxygenated compounds in a 'Grob' sample. Ion losses based on SIMION ion trajectory predictions were consistent with experimental findings. CONCLUSIONS: We demonstrated that the use of high-frequency QIGs can extend the operational lower m/z range for both external EI- and ESI-FTICR mass spectrometers. By considering both ICR and Mathieu equations of motions to describe ion trajectories, theoretical ion ejection thresholds (consistent with our experimental findings) could be predicted.

An assessment of the liquid-gas partitioning behavior of major wastewater odorants using two comparative experimental approaches: liquid sample-based vaporization vs. impinger-based dynamic headspace extraction into sorbent tubes.

The gas-liquid partitioning behavior of major odorants (acetic acid, propionic acid, isobutyric acid, n-butyric acid, i-valeric acid, n-valeric acid, hexanoic acid, phenol, p-cresol, indole, skatole, and toluene (as a reference)) commonly found in microbially digested wastewaters was investigated by two experimental approaches. Firstly, a simple vaporization method was applied to measure the target odorants dissolved in liquid samples with the aid of sorbent tube/thermal desorption/gas chromatography/mass spectrometry. As an alternative method, an impinger-based dynamic headspace sampling method was also explored to measure the partitioning of target odorants between the gas and liquid phases with the same detection system. The relative extraction efficiency (in percent) of the odorants by dynamic headspace sampling was estimated against the calibration results derived by the vaporization method. Finally, the concentrations of the major odorants in real digested wastewater samples were also analyzed using both analytical approaches. Through a parallel application of the two experimental methods, we intended to develop an experimental approach to be able to assess the liquid-to-gas phase partitioning behavior of major odorants in a complex wastewater system. The relative sensitivity of the two methods expressed in terms of response factor ratios (RFvap/RFimp) of liquid standard calibration between vaporization and impinger-based calibrations varied widely from 981 (skatole) to 6,022 (acetic acid). Comparison of this relative sensitivity thus highlights the rather low extraction efficiency of the highly soluble and more acidic odorants from wastewater samples in dynamic headspace sampling.

An exploration on the suitability of airborne carbonyl compounds analysis in relation to differences in instrumentation (GC-MS versus HPLC-UV) and standard phases (gas versus liquid).

The relative performance figure of merits was investigated for the two most common analytical methods employed for carbonyl compounds (CC), for example, between high performance liquid chromatography (HPLC)-UV detector (with 2,4-dinitrophenylhydrazine (DNPH) derivatization) and thermal desorption (TD)-gas chromatography (GC)-mass spectrometry (MS) (without derivatization). To this end, the suitability of each method is assessed by computing the relative recovery (RR) between the gas- and liquid-phase standards containing a suite of CC such as formaldehyde (FA), acetaldehyde (AA), propionaldehyde (PA), butyraldehyde (BA), isovaleraldehyde (IA), and valeraldehyde (VA) along with benzene (B) as a recovery reference for the GC method. The results confirm that a TD-GC-MS is advantageous to attain the maximum recovery for the heavier CCs (i.e., with molecular weights (MW) above BA-MW ≥ 74). On the other hand, the HPLC-UV is favorable for the lighter CCs (like FA and AA) with the least bias. Such compound-specific responses for each platform are validated by relative ordering of CCs as a function of response factor (RF), method detection limit (MDL), and recovery pattern. It is thus desirable to understand the advantages and limitations of each method to attain the CC data with the least experimental bias.