Volatile Organic Species Research Articles

Hygroscopic behavior of partially volatilized coastal marine aerosols using the volatilization and humidification tandem differential mobility analyzer technique

Coastal marine nucleation, Aitken, and accumulation mode aerosol particles with back trajectories indicative of marine origin were examined using a volatilization and humidification tandem differential mobility analyzer (VHTDMA) to reveal the volatilization temperatures of the various component species. The diameter hygroscopic growth factors of the residue particles were continually examined throughout the volatilization process. In each of the three modes the dominant particle type appeared to be composed of the same four physicochemically distinct species though in different ratios. These species exhibited volatility and hygroscopic behavior consistent with combinations of a volatile organic species, sulfuric acid, ammonium sulfate or bisulfate, iodine oxide, and an insoluble nonvolatile residue. The Aitken and accumulation mode aerosols contain large fractions of the insoluble, volatile, organic‐like material, and the volatilization of this species results in a distinct increase in the water volume uptake of the particles. Of the four distinct species, only the sulfuric acid‐like species constituted an increasing volume fraction with decreasing particle size. This finding indicates that nucleation mode particles constitute an acidic seed and as such would undergo acid‐catalyzed secondary organic aerosol growth at a faster rate. The lack of a nonvolatile hygroscopic residue consistent with sea salt in these particles implies that the aerosolization of seawater is not the dominant production mechanism for these submicrometer coastal marine aerosols.

Determination of in situ-generated dimethyldioxirane from an aqueous matrix using selected ion monitoring

There is a growing interest in utilizing in situ-generated dimethyldioxirane (DMDO) as an oxidant for synthetic purposes and bleaching and decontamination applications, but the ability to quantify the organic cyclic peroxide species is often complicated by the presence of other reactive components, peroxymonosulfate and acetone, within the solution matrix. This paper is the first to report the use of a MS method for the quantitation of DMDO from these complex matrices by utilizing an isothermal 30 °C GC program in conjunction with selected ion monitoring (SIM). The volatile organic species is sampled from the headspace of closed batch system vials and quantified by measuring the abundance of m/ z 74. The method achieves a practical quantitation limit (PQL) for DMDO of 0.033 mM, and methyl acetate is identified as a minor decomposition product from the aqueous sample matrix, contributing 9% towards the overall DMDO measurements. The spectroscopic method makes use of common analytical instrumentation and is capable of measuring other in situ-generated dioxiranes, such as those generated from 2-butanone and [ 2H 6]acetone.

Nanoparticle formation by ozonolysis of inducible plant volatiles

Abstract. We present the first laboratory experiments of aerosol formation from oxidation of volatile organic species emitted by living plants, a process which for half a century has been known to take place in the atmosphere. We have treated white cabbage plants with methyl jasmonate in order to induce the production of monoterpenes and certain less-volatile sesqui- and homoterpenes. Ozone was introduced into the growth chamber in which the plants were placed, and the subsequent aerosol formation and growth of aerosols were monitored by measuring the particle size distributions continuously during the experiments. Our observations show similar particle formation rates as in the atmosphere but much higher growth rates. The results indicate that the concentrations of nonvolatile oxidation products of plant released precursors needed to induce the nucleation are roughly an order-of-magnitude higher than their concentrations during atmospheric nucleation events. Our results therefore suggest that if oxidized organics are involved in atmospheric nucleation events, their role is to participate in the growth of pre-existing molecular clusters rather than to form such clusters through homogeneous or ion-induced nucleation.

Volatile organoselenium monitoring in production and gastric digestion processes of selenized yeast by solid‐phase microextraction‐multicapillary gas chromatography coupled microwave‐induced plasma atomic emission spectrometry

AbstractEvolution of volatile organoselenium compounds in the production and gastric digestion of selenized yeast has been monitored. The industrial production of these kinds of material, employed as food supplements, has been simulated in a process of yeast enrichment with inorganic selenium selenium (IV) in different growth media, with variation of the pH value. The in vitro gastric digestion process was carried out with pepsin in an acid and salt mixture. Determination of volatile species of selenium was achieved coupling solid‐phase microextraction (SPME) for preconcentration and sample–matrix separation and microwave‐induced plasma atomic emission spectrometry, in combination with multicapillary (MC) gas chromatography for separation and detection of the selenium species. The MC column was operated at low temperatures (∼30 °C). The method was optimized, using a chemometric approach, with respect to the detection of organoselenium species such as dimethylselenide, diethylselenide and dimethyldiselenide. SPME sampling was carried out in the headspace above the corresponding solutions. Separation is fast, with a chromatogram being obtained in less than 5 min, and the detection limits were at the low parts per billion level for all species investigated. The results of the yeast enrichment process demonstrate inorganic selenium transformation into volatile organic species. The presence of inorganic selenium gave rise to at least five different volatile species after metabolization by yeast, with dimethylselenide and dimethyldiselenide being the predominant species. Commercial pasteurized yeast, containing mainly selenomethionine for use as a food supplement, and tablets were found to be still active under conditions of the simulation of the digestion process, even though producing relatively low amounts of organoselenium compounds. Copyright © 2004 John Wiley & Sons, Ltd.

Probing the microwave degradation mechanism of phenol-containing polymeric compounds by sample pretreatment and GC–MS analysis

We have detected the volatile organic species obtained after microwave digestion of poly(hydroxystyrene) with nitric acid in closed vessels at various reaction temperatures by using headspace solid-phase microextraction (HS–SPME) and gas chromatography/mass spectrometry (GC–MS). We probed the digestion reaction by measuring the response of the detectable species – we detected a total of 20 volatile organic compounds – with respect to the temperature over the range from room temperature to 80 °C. These compounds can be classified into alkane, alkanol, and aromatic species. The alkane species decreased monotonically, whereas the alkanol and aromatic compounds first increased and then decreased, as the digestion temperature increased. We have established the degradation mechanisms, which involve bond scission, recombination, adduct formation, and ring opening, on the basis of product analyses and bond length simulations.

Development of ion drift-chemical ionization mass spectrometry.

An ion drift-chemical ionization mass spectrometry (ID-CIMS) technique has been developed to detect and quantify trace gases, including volatile organic compounds and inorganic species. The trace species are chemically ionized into positive or negative product ions with a well-controlled ion-molecule reaction time. The ID-CIMS method allows for quantification of the trace gases without the necessity of performing calibrations with authentic standards for the trace gases. Demonstrations of the ability of ID-CIMS to accurately quantify isoprene and HNO3 in a laboratory setting are presented. The results illustrate that the ID-CIMS technique facilitates detection and quantification of organic and inorganic species in laboratory kinetic investigations and field measurements.

Variation in the Optical Sensing Responses toward Vapors of a Porphyrin/Phthalocyanine Hybrid Thin Film

Spin-coated layers of zinc(II) tetra-4-(2,4-di-tert-amylphenoxy)phthalocyanine (ZnPctamyl) and copper(II) tetrakis(p-tert-butylphenyl)porphyrin (CuPtphen) have been synthesized and used as solid state chemically interacting materials deposited in thin film form for the detection of alcohols, amines, ketones, alkanes, and pyridines for applications in food quality control. The UV−Vis variations obtained by the exposure of the sensing layers to the mentioned analytes in controlled atmosphere have been analyzed and compared with those deriving by a single thin film obtained by mixing the two metal complexes in an appropriate ratio. A multichannel monitoring of the main bands of the sensing layer due to the interaction with the analyte vapors became the basis to construct a set of independent sensors located on a single sensing element. The effects in the variation of the absorption bands of the blend system are compared with the variations in absorbance observed with the two sensing layers fabricated separately with each single compound. The interaction between some volatile organic compound species and the heterogeneous sensing layer shows a different behavior in the responses with respect to the results obtained with each single compound.

Volatile organo-selenium speciation in biological matter by solid phase microextraction–moderate temperature multicapillary gas chromatography with microwave induced plasma atomic emission spectrometry detection

Microwave induced plasma atomic emission spectrometry (MIP-AES) in combination with multicapillary (MC) gas chromatography could be proven to be useful for element specific detection of volatile species. Solid phase microextraction (SPME) was used for preconcentration and sample-matrix separation. The fiber desorption unit as well as the heating control for the MC column were in-house developed and multicapillary column was operated at moderate temperatures (30–100 °C). The method was optimized for organo-selenium species (dimethylselenide (DMSe), diethylselenide (DEtSe) and dimethyldiselenide (DMDSe)), using a chemometric approach. Stationary phases for the separation column were optimized using a conventional GC and contrasted with the results obtained with the MC. Application was focussed on selenium accumulating biological matter, such as lupine, yeast, Indian mustard and garlic. These samples were grown in hydroponic solution containing inorganic selenium (Na 2SeO 3 and Na 2SeO 4). SPME sampling was carried out in fixed volume flow boxes in headspace above the living plants and in vials using treated samples. Results demonstrate inorganic selenium transformation into volatile organic species during metabolism. Separation is fast, a chromatogram can be obtained in less than 3 min and detection limits were at sub-ppb level for all investigated species. The system is independent from the use of a conventional gas chromatographic oven and can be used as a versatile alternative to highly cost intensive methods such as GC–ICP-MS.

Microbial participation in iodine volatilization from soils.

The roles of microorganisms in iodine volatilization from soils were studied. Soils were incubated with iodide ion (I-), and volatile organic iodine species were determined with a gas chromatograph. Iodine was emitted mainly as methyl iodide (CH3I), and CH3I emission was sometimes enhanced by the addition of glucose. Soils were then incubated with a radioactive iodine tracer (125I), and radioiodine emitted from soils was determined. The emission of iodine was enhanced in the presence of yeast extract but was inhibited by autoclaving of soils. The addition of streptomycin and tetracycline, antibiotics that inhibit bacterial growth, strongly inhibited iodine emission, while a fungal inhibitor cycloheximide caused little effect. Forty bacterial strains were randomly isolated from soils, and their capacities for volatilizing iodine were determined. Among these, 14 strains volatilized significant amounts of iodine when they were cultivated with iodide ion. Phylogenetic analysis based on 16S ribosomal DNA sequences showed thatthese bacteria are widely distributed through the bacterial domain. Our results suggest that iodine in soils is methylated and volatilized as CH3I by the action of soil bacteria and that iodine-volatilizing bacteria are ubiquitous in soil environments. The pathway of iodine volatilization by soil bacteria should be important for understanding the biogeochemical cycling of iodine as well as for the assessment of long-lived radioactive iodine (129I) in the environment.

Catalytic combustion of methane in the presence of organic and inorganic compounds over La0.9Ce0.1CoO3 catalyst

The catalytic combustion of the emission from coke ovens containing various volatile organic compounds (VOCs) and inorganic species over a La0.9Ce0.1CoO3 catalyst is investigated in an integral fixed reactor through several steps. (1) Combustion of a mixture of VOC reveals that the kinetics of total oxidation of methane determines the total VOC conversion. (2) The conversion of methane, in the case of sulfur-free feed is inhibited by H2O and CO2.

Combustion toxicity of fire retarded EVA

A Purser furnace has been used to investigate the combustion toxicity of ethylene-vinyl acetate copolymer (EVA) with and without fire retardants, under different fire conditions. Steady state flaming combustion has been studied at equivalence ratios φ varying from 0.5 to 1.5 by driving the materials through the furnace at 750 °C. Yields of CO and CO 2 for EVA containing 27% vinyl acetate, and its fire retarded composites, containing fire retardant fillers are presented. The materials contained 30% EVA and 70% hydrated aluminium oxide (ATH), or 65% ATH and 5% zinc hydroxystannate (ZS), or 5% magnesium borate (MgB) or 5% zinc borate (ZB). In each case the same mass of EVA was used in the determination. The yields of CO per g of polymer from the EVA-fire retardant composite samples showed very similar yields of CO under well ventilated conditions to the pure EVA, but generally higher CO yields than the base polymer under the most toxic fuel rich conditions. The exception to this was the sample containing ATH and zinc borate, which did not take up all the available oxygen under fuel rich conditions, and gave a much lower CO yield, corresponding to an eight-fold reduction in the combustion toxicity. Under fuel rich conditions for EVA, 60% of the carbon was lost as volatile organic species other than CO and CO 2. For the sample containing zinc borate, this was 50% and for the remaining samples it varied from 20 to 38%. Evidence is presented which indicates that organic material trapped in the solid alumina residue is oxidised to CO, except in the presence of zinc borate, when it appears to be lost as organic carbon.

Plasma treatment of polycarbonate for improved adhesion

The deposition of silicon alloys for protective and optical coatings on polymers is of increasing interest. The understanding of the plasma polymer interaction is of prime importance here. In this work, we report a study of the influence of N2, H2, and O2 plasma treatments on pure and commercial grade polycarbonate (PC) in order to enhance the adhesion of plasma deposited silica films. Treatments and depositions were carried out in a low pressure (1 mTorr range) integrated distributed 2.45 GHz microwave electron cyclotron resonance reactor, which allows the deposition of dense stoechiometric silica at room temperature. The plasma–polymer interaction is studied by in situ UV-visible spectroscopic ellipsometry on thin spin-coated PC films. The absorption in the PC layer was found to increase in the UV which was attributed to the different reaction products of photo-Fries rearrangements, especially for pure PC. Gel permeation chromatography measurements showed that the major influence of plasma treatment on pure polycarbonate is chain scission opposed to crosslinking in the case of commercial grade PC, indicating that additives present in commercial grade PC play a major role in the crosslinking mechanisms. The plasma treatment modifies the top 330 nm/homogeneously and no indication of a high index surface layer (50–200 nm) or gradient was found. This is attributed to the low pressure of the plasma treatment, which makes a redeposition of volatile organic species unlikely.

Complex effects arising in smoke plume simulations due to inclusion of direct emissions of oxygenated organic species from biomass combustion

Oxygenated volatile organic species (oxygenates), including HCOOH, H2CO, CH3OH, HOCH2CHO (hydroxyacetaldehyde), CH3COOH, and C6H5OH, have recently been identified by Fourier transform infrared measurements as a significant component of the direct emissions from biomass combustion. These oxygenates have not generally been included in the hydrocarbon‐based initial emission profiles used in previous photochemical simulations of biomass combustion smoke plumes. We explore the effects of oxygenates on this photochemistry by using an established initial emission hydrocarbon profile and comparing simulation results obtained both with and without addition of the above six oxygenates. Simulations are started at noon and carried out for 30 hours in an expanding Lagrangian plume. After an initial transient period during which [NOx] falls rapidly, conditions within the oxygenated smoke plume are found to be strongly NOx‐sensitive, and the simulated final species profile is thus strongly dependent upon the Δ[NO]/Δ[CO] initial emission profile. Oxygenate addition results in very significant and complex effects on net O3production, as well as on the relative amounts of long‐lived HOxand NOxreservoir species (H2O2, organic hydroperoxides, HNO3, and peroxyacetyl nitrate (PAN)) that are mixed into the surrounding atmosphere. Oxygenates may either increase or decrease net O3production (depending upon the initial Δ[NO]/Δ[CO]). However, they always increase H2O2and organic hydroperoxide production as a result of increased rates of radical + radical reactions. These effects spring largely from accelerated removal of NOxfrom the smoke plume due to increased radical concentrations resulting both from photolysis of oxygenates (mainly CH2O) and from their relatively high reactivity. Predicted concentrations of H2O2, Δ[O3]/Δ[CO], Δ[NH3]/Δ[CO], and Δ[HCOOH]/Δ[CO] are compared with some available measured values.

On the Hygroscopic Behavior of Atmospheric Organic Aerosols

The vapor−liquid equilibrium of organic species and water determines the partitioning of volatile organic species between the gas and aerosol phases in the atmosphere. Essential properties that govern this partitioning are the compounds' vapor pressures and the liquid-phase activity coefficients of the organic species. Key issues include (1) the amount of water absorbed by organic particles, both single-component and multicomponent, as a function of relative humidity and (2) how organic and water partitioning is altered as the relative humidity changes, for a fixed total (gas plus particle) quantity of each organic component. We present here calculations relating to each of these issues for organic molecules that are characteristic of those that have been identified in ambient aerosols. Uncertainties exist in knowledge of vapor pressures of atmospheric organics and in activity coefficients, which are calculated by the UNIFAC method. These uncertainties, the level of which is difficult to estimate because of a lack of appropriate thermodynamic data, can lead to significant uncertainty in predicted gas−aerosol partitioning. Current theories for estimating both vapor pressures and activity coefficients are likely to be improved eventually, but the methods discussed here will probably remain the procedures of choice for the immediate future.

Separation methods for environmental technologies

AbstractMuch of the environmental damage in air, soil, sediment, surface and groundwater can be repaired, and further damage prevented through the use of efficient separation technologies. Such technologies should typically achieve higher degrees of species separation. Environmental contamination requires remediation separation technologies especially suited for very low concentrations. This paper highlights the separation and recovery of volatile organic compounds and toxic metal species. Conventional separation technologies are currently inefficient and costly. In this paper, the scope of separation science and technologies in environmental areas will be outlined, and several promising emerging ideas in the areas of sorption and membranes are discussed. The authors view high surface area membrane‐based sorption as a common approach that shows significant promise for tackling these difficult problems by improving technical capability, operability, and process economics.

Coupling Pervaporation-Gas Chromatography for Speciation of Volatile Forms of Selenium in Sediments

A method for speciation of dimethylselenide (DMeSe), dimethyldiselenide (DMeDSe) and diethylselenide (DEtSe) in sediments based on a coupling between a pervaporation module, a preconcentration sorptive trap and a gas chromatograph-mass spectrometer is reported. The coupling is performed through a high pressure injection valve which allows two different operational modes: (a) analysis without preconcentration, in which analytes are directly driven from the pervaporation chamber to the injection port of the chromatograph, and (b) analysis with preconcentration in a trap, in which the analytes from the pervaporation chamber are first trapped on a Tenax minicolumn and then thermally desorbed and driven to the GC. This second approach improves the sensitivity compared to the direct coupling, reaching estimated absolute detection limits lower than 0.6 ng Se for each tested species. The method is applied to the determination of volatile organic selenium species in several sediments collected from different areas in the Southwest of Spain.

Radioanalytical Determination of Biogenic Volatile Iodine Emitted from Aqueous Environmental Samples

A reliable method using 125I tracer for direct determination of volatile iodine formed in aqueous environmental samples was established. Soil solution, seawater and bacterial cell suspension were selected as model samples, and incubated with 125I−. Volatile inorganic and organic iodine species produced during incubation were collected in silver wool and activated charcoal traps, separately the efficiency of the traps, the storage conditions of 125I− stock solution and the procedures to expel the dissolved volatile iodine from the sample solutions were examined. Formation of biological volatile iodine was observed in all samples, and the dominant iodine species was found to be organic iodine. The advantages of this method are its simplicity, low cost and low detection limit.

Stability and Storage Problems in Selenium Speciation from Environmental Samples

The stability of selenite and selenate at 0.3 and 100 μg L−1 concentrations, preserved at different pH values (pH 2, 4 and 8) and stored in different containers (Teflon, polypropylene and polyethylene) at various temperatures (from −20 to 40°C) was studied for one year period. Both species were stable in acidified samples at pH 2 with HCl at −20°C in Teflon containers for the twelve months tested. However, losses of selenite were observed after 6 months in river and tap water samples. Selenate was more stable than selenite and higher concentrations were more stable than lower concentrations. The order of decreasing stability was Teflon > polyethylene > polypropylene, pH 2 > pH 4 > pH 8 and −20°C > 4°C > 25°C > 40°C. The stability of four volatile organic selenium species in seawater spiked at concentrations of 50 μg L−1 for both DMSe and DESe and at concentrations of 0.50 μg L−1 for both DMDSe and DEDSe, stored at two temperatures (4°C and −20°C) in three different container materials (Teflon, polyethylene and polystyrene) was studied. The four species were only stable for 24 h. The order of decreasing stability was DMDSe > DESe > DEDSe > DMSe, Teflon > polyethylene > polystyrene and −20°C > 4°C.

Speciation of volatile forms of selenium and inorganic selenium in sediments by gas chromatography–mass spectrometry

Methods are presented for the speciation of both inorganic and organic compounds of selenium, including selenite, selenate, dimethylselenide (DMSe), dimethyldiselenide (DMDSe), diethyselenide (DESe) and diethyldiselenide (DEDSe). Parameters affecting the extraction efficiency from sediments are discussed and the performance of the methods is described. Inorganic selenium species are quantitatively leached from sediments using alkaline solutions. Separation of selenite and selenate is carried out using anion-exchange phases packed in cartridges. Selenite is analysed as piaselenol derivative using GC–MS. Selenate is determined after conversion into selenite. The detection limit achieved using the proposed method is 0.6 ng of Se g −1 (wet mass basis) for both selenite and selenate using sample portions of 1 g. Volatile selenium species are desorbed from sediments using a dynamic headspace desorption method with active carbon as sorptive trap. The species are eluted with carbon disulphide. The four organic selenium species are directly analysed by GC–MS but sensitivity of the method is improved for dialkyldiselenides after derivatization with 1-fluoro-2,4-dinitrobenzene followed by extraction into ethyl acetate and evaporation to dryness under a N 2 stream. Extraction recoveries obtained by this method are higher than 75% for all the species considered in the present work. Estimated detection limits for DMSe, DMDSe, DESe and DEDSe using portions of 20 g of wet sediments are 33, 1.0, 22 and 2.3 ng of Se g −1 (wet mass basis). The methods were applied to the determination of inorganic and volatile organic selenium species in several sediments collected from different areas in the Southwest of Spain. Finally, incubation experiments were performed at two temperatures for 15 days on sediments and a raw sewage sludge collected from Ayamonte city. Only from this latter were both DMDSe and DESe generated.

Plasma-deposited silicon oxide and silicon nitride films on poly(ethylene terephthalate): A multitechnique study of the interphase regions

The “interphase” region between the deposited layer [e.g., plasma-enhanced chemically vapor deposited (PECVD) SiO2 or SiN] and the poly(ethylene terephthalate) (PET) substrate has been investigated and compared to physical vapor deposited (PVD) (electron beam evaporated) SiO2. Composition profiles determined by time-of-flight elastic recoil detection, electron microprobe analysis, and x-ray photoelectron spectroscopy all show an extended interphase region more than 50 nm in width, while the profile of the PVD SiO2 is narrower. However, since these analytical techniques are invasive and prone to artifacts, we have also examined ultrathin (about 10 and 20 nm) SiO2 and SiN PECVD layers on 50 nm spin-coated PET substrates by nondestructive infrared (IR) techniques. The IR spectra confirm that the thin PECVD deposits also comprise an organosilicon phase with Si–CHx bonds. We explain these observations in terms of a fragmentation/redeposition mechanism: During the earliest stage of PECVD, interaction between the plasma and the polymer surface produces volatile organic species, which intermix with the reagent gas feed, thus giving rise to the observed organosilicon-like deposit with gradually decreasing carbon content.