Compounds In Gas Phase Research Articles

Passive Air Sampler (PAS)와 기체/입자 분배모델을 이용한 대기 중 PCB 농도 산정

Polyurethane foam-disk passive air samplers (PAS) were deployed in a southern area of Korea for three months. The target compounds were 12 coplanar polychlorinated biphenyls (PCBs). The congener profiles measured in this study were the same as those in ambient air and emission gas from the incinerator. A gradient of the total PCBs in different regions (industrial>residential>rural) was observed, suggesting the industrial complex may be an important source of coplanar PCBs. In general, only gas-phase compounds are mainly sequestrated by PAS. In order to estimate the concentration of particle-phase PCBs, a gas/particle partition model was used. A combined result (gas+particle-phase PCBs) was compared with previous results, indicating that the level of coplanar PCBs in our study area is comparable to those in other urban sites in the world. The validation of this method for estimating the total concentration is required through additional backup studies.

Assessing the Influence of Meteorological Parameters on the Performance of Polyurethane Foam-Based Passive Air Samplers

Polyurethane foam (PUF) disk passive air samplers were evaluated under field conditionsto assessthe effect of temperature and wind speed on the sampling rate for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and organochlorine pesticides (OCPs). Passive samples integrated over 28-day periods were compared to high-volume air samples collected for 24 h, every 7 days. This provided a large data set of 42 passive sampling events and 168 high-volume samples over a 3-year period, starting in October 2003. Average PUF disk sampling rates for gas-phase chemicals was approximately 7 m3 d(-1) and comparable to previous reports. The high molecular weight PAHs, which are mainly particle-bound, experienced much lower sampling rates of approximately 0.7 m3 d(-1). This small rate was attributed to the ability of the sampling chamber to filter out coarse particles with only the fine/ultrafine fraction capable of penetration and collection on the PUF disk. Passive sampler-derived data were converted to equivalent air volumes (V(EQ), m3) using the high-volume air measurement results. Correlations of V(EQ) against meteorological data collected on-site yielded different behavior for gas- and particle-associated compounds. For gas-phase chemicals, sampling rates varied by about a factor of 2 with temperature and wind speed. The higher sampling rates at colder temperatures were explained bythe wind effecton sampling rates. Temperature and wind were strongly correlated with the greatest winds at coldertemperatures. Mainly particle-phase compounds (namely, the high molecular weight PAHs) had more variable sampling rates. Sampling rates increased greatly atwarmertemperatures as the high molecular weight PAH burden was shifted toward the gas phase and subject to higher gas-phase sampling rates. At colder temperatures, sampling rates were reduced as the partitioning of the high molecular weight PAHs was shifted toward the particle phase. The observed wind effect on sampling for the particle-phase compounds is believed to be tied to this strong temperature dependence on phase partitioning and hence sampling rate. For purposes of comparing passive sampler derived data for persistent organic pollutants, the factor of 2 variability observed for mainly gas-phase compounds is deemed to be acceptable in many instances for semiquantitative analysis. Depuration compounds may be used to improve accuracy and provide site-specific sampling rates, although this adds a level of complexity to the analysis. More research is needed to develop and test passive air samplers for particle-associated chemicals.

X-ray, 1H NMR and DFT study on 5- para-X-benzylidene-thiazolidine derivatives with X = Br, F

Experimental methods (NMR spectroscopy and X-ray diffraction) and quantum chemical calculations based on density functional theory (DFT) were used for structural and electronic characterization of two thiazolidine-2-thione-4-one derivatives with antimicrobial activity, namely 5- para-bromo-benzylidene-thiazolidine-2-thione-4-one (5pBr-BTT) and 5- para-fluoro-benzylidene-thiazolidine-2-thione-4-one (5pF-BTT). X-ray diffraction technique indicates that 5pBr-BTT crystallizes with one DMSO solvent molecule, forming a 1:1 5pBr-BTT·DMSO complex, in the triclinic space group P 1 ¯ , with Z = 2 and cell parameters a = 4.4597(7) Å, b = 12.5508(19) Å, c = 13.7270(2) Å, α = 90.75(2)°, β = 96.23(2)° and γ = 97.86(3)°. The linear conformation adopted in the crystalline state is established by intermolecular hydrogen bonds formed between oxygen atoms from DMSO and the thione group. 5pF-BTT crystallizes in the monoclinic space group P2 1/ c with Z = 4 and cell parameters a = 4.9161(4) Å, b = 19.9008(17) Å, c = 10.4934(9) Å and β = 92.90(2)°; these molecules form a wave-like arrangement along the c axis, with direct intermolecular hydrogen bonds (HBs). The lowest energy optimized geometries of the investigated compounds in gas-phase correspond to thionic tautomers and they are consistent with those obtained by X-ray technique. Tautomeric equilibrium between the thione, thiol and enol forms of the two compounds have been considered and analyzed by theoretical methods. While crystal structures correspond to the thione forms, the investigated compounds show thione–thiol tautomerism in DMSO solution, this conclusion being supported by theoretical results obtained by using the PCM solvation model. On the other hand, the continuum PCM solvation model fails to describe the experimental chemical shift associated with the NH proton in the thione form of the two compounds, but a very good correlation between experiment and theory was obtained by taking into account the specific solute–solvent interactions.

THEORETICAL CALCULATION OF BOND DISSOCIATION ENERGIES AND HEATS OF FORMATION FOR ALKYL NITRATE AND NITRITE COMPOUNDS WITH DENSITY FUNCTIONAL THEORY AND COMPLETE BASIS SET METHOD

The N – O bond dissociation energies (BDEs) and the heats of formation (HOFs) of alkyl nitrate and nitrite compounds in gas phase at 298.15 K were theoretically calculated. Density functional theory (B3LYP and PBE1PBE) with 6-311+g** and 6-311g** basis sets was employed. It is found that PBE1PBE functional has an average increased BDE of 4.03 kcal/mol from B3LYP functional. What is more, we find the reverse trend in ab initio approach, which is slightly smaller than PBE1PBE. The B3LYP functional is found to be sufficiently reliable to compute the BDEs of alkyl nitrate compounds without the presence of diffusion functions. The BDEs of alkyl nitrite compounds appear to be a constant. The functionals (B3LYP and PBE1PBE) with 6-311g** and 6-311+g** basis sets and CBS-4M ab initio method can all yield good results with respect to the experimental HOFs with the deviation less than 2.0 kcal/mol. As the number of methylene group increases, the HOFs of alkyl nitrate and nitrite compounds increase. In addition, the conclusion of Ventural et al. (J Phys Chem A105:9912, 2001 and Phys Lett245:488, 1995) is confirmed again by our computational results.

Modeling and simulation of materials synthesis: Chemical vapor deposition and infiltration of pyrolytic carbon

Chemical vapor deposition and infiltration of pyrolytic carbon for the production of carbon fiber reinforced carbon is studied by modeling approaches and computational tools developed recently. Firstly, the development of a gas-phase reaction mechanism of chemical vapor deposition (CVD) of carbon from unsaturated light hydrocarbons (C 2H 4, C 2H 2, and C 3H 6) is presented. The mechanism consisting of 827 reactions among 227 species is based on existing information on elementary reactions and evaluated by comparison of numerically predicted and experimentally determined product compositions taking into account 44 stable gas-phase compounds formed in a tubular flow reactor. Secondly, a model and a computer code for two-dimensional transient simulations of chemical vapor infiltration (CVI) from methane into carbon fiber reinforced carbon are presented. The chemical model is based on a reduced multi-step reaction scheme for pyrolytic carbon deposition, which is derived from a mechanism based on elementary reactions, and a hydrogen inhibition model of pyrolytic carbon deposition. The coupled governing equations of mass transfer, chemical vapor deposition, surface growth, and gas-phase and surface chemical reactions are numerically solved by a finite element method (FEM). The computer code is applied to reveal densification processes of felts with fiber volume fractions of 7.1% and 14.2%. Numerically predicted bulk density distributions agree well with experimental results.

Retention of arsenic and selenium compounds present in coal combustion and gasification flue gases using activated carbons

The emission of potentially toxic compounds of arsenic and selenium present in flue gases from coal combustion and gasification processes has led to the need for gas cleaning systems capable of reducing their content. This work is focused on the capture of these elements in activated carbons which have proven to have good retention capacities for mercury compounds in gas phase. Two commercial activated carbons (Norit RBHG3 and Norit RB3) and a carbon prepared via activation of a pyrolysed coal (CA) were tested in simulated coal combustion and gasification atmospheres in a laboratory scale reactor. Arsenic and selenium compounds were retained to different extents on these carbons, retention efficiency depending mainly on the speciation of the element, which in turn depends on the gas atmosphere. Arsenic retention was similar in both combustion and gasification atmospheres unlike selenium retention. Moreover the retention of arsenic was lower than that of selenium.

Atmospheric deposition of nitrogen, sulfur and chloride in Thessaloniki, Greece

In the present study, the wet and dry depositions of particulate NO 3 −, SO 4 2−, Cl − and NH 4 + were measured using a wet/dry sampler as a surrogate surface. Gas phase compounds of nitrogen, sulfur and chloride (HNO 3, NH 3, SO 2 and HCl) were measured by an annular denuder system (ADS) equipped with a back up filter for the collection of particles with diameter ≤ 5 μm. Ambient concentrations of NO, NO 2 and SO 2 were also taken into consideration. Sampling was conducted at an urban site in the center of the city of Thessaloniki, northern Greece. The presence of the aerosol species was examined by cold/warm period and the possible compounds in dry deposits were also considered. Dry deposition fluxes were found to be well correlated with ambient particle concentrations in order to be used for the calculation of particle deposition velocity. Average particulate deposition velocities calculated were 0.36, 0.20, 0.20 and 0.10 cm s − 1 for Cl −, NO 3 −, SO 4 2− and NH 4 +, respectively. Total dry deposition fluxes (gas and particles) were estimated at 3.24 kg ha − 1 year − 1 for chloride (HCl + p-Cl), 9.97 kg ha − 1 year − 1 for nitrogen oxidized (NO + NO 2 + HNO 3 + p-NO 3), 5.32 kg ha − 1 year − 1 for nitrogen reduced (NH 3 + p-NH 4) and 15.77 kg ha − 1 year − 1 for sulfur (SO 2 + p-SO 4). 70–90% total dry deposition was due to gaseous species deposition. The contribution of dry deposition to the total (wet + dry) was at the level of 60–70% for sulfur and nitrogen (oxidized and reduced), whereas dry chloride deposition contributed 35% to the total. The dry-to-wet deposition ratio of all the studied species was found to be significantly associated with the precipitation amount, with nitrogen species being better and higher correlated. Wet, dry and total depositions measured in Thessaloniki, were compared with other countries of Europe, US and Asia.

Bond and site selectivity in dissociative electron attachment to gas phase and condensed phase ethanol and trifluoroethanol

The formation of negative ions following electron impact to ethanol (CH(3)CH(2)OH) and trifluoroethanol (CF(3)CH(2)OH) is studied in the gas phase by means of a crossed electron-molecular beam experiment and in the condensed phase via Electron Stimulated Desorption (ESD) of fragment ions from the corresponding molecular films under UHV conditions. Gas phase ethanol exhibits two pronounced resonances, located at 5.5 eV and 8.2 eV, associated with a remarkable selectivity in the decomposition of the precursor ion. While the low energy resonance exclusively decomposes into O(-), that at higher energy generates OH(-) and a comparatively small signal of [CH(3)CH(2)O](-) due to the loss of a neutral hydrogen. CF(3)CH(2)OH shows a completely different behaviour, as now an intense feature at 1.7 eV appears associated with the loss of a neutral hydrogen atom exclusively occurring at the O site. The H(-) formation from the gas phase compounds is below the detection limit of the present experiment, while in ESD from 3 MonoLayer (ML) films of CH(3)CH(2)OH and CF(3)CH(2)OH the most intense fragment is H(-), appearing from a broad resonant feature between 7 and 12 eV. With CF(3)CH(2)OH, by using the isotopically-labelled analogues CF(3)CD(2)OH and CF(3)CH(2)OD it can be shown that this feature consists of two resonances, one located at 8 eV leading to H(-)/D(-) loss from the O site and a second resonance located at 10 eV leading to the loss of H(-)/D(-) from the CH(2) site.

Reactivity of NH 3 and HCN during low-grade fuel combustion in a swirling flow burner

The experimentally measured major gas species profiles in the near-burner region provide insight on flame structure and pollutant formation mechanisms during pilot-scale biomass, coal, and biomass-coal cofiring tests. All tests involved separately metered but jointly fed coal and biomass in a variable-swirl burner. Locally fuel-rich regions form under overall fuel-lean conditions, as is typical of such flames, although there are no regions of the combustor that indicate average oxygen concentration reaches zero. The data strongly suggest that instantaneous oxygen concentrations reach zero, so the average finite values are indicative of turbulent intermittency between fuel-rich and fuel-lean eddies. Such intermittency impacts the entire flame structure in these and many previously published flames, though this feature may not be widely appreciated. Detectable HCN concentrations appear in the fuel-rich eddies in the coal-dominated flames with little or no detectable NH 3 whereas NH 3 appears in the biomass-dominated flames with little or no detectable HCN. These data indicate that biomass predominantly forms NH 3 whereas coal predominantly forms HCN as stable, fuel-rich, gas-phase compounds. Kinetics calculations demonstrate that NH 3 has higher thermal stability and is more reactive within the flame front than HCN. Both species have similar conversion to NO at the same temperatures. The results confirm that NO x precursor formation depends on the parent fuel and form of nitrogen, at least for the coal and biomass fuels investigated here.

Cross flow ion mobility spectrometry: Theory and initial prototype testing

By marrying the concepts behind ion mobility spectrometry (IMS) and differential mobility analysis (DMA), a new instrument, the Cross Flow Ion Mobility Spectrometer (CF-IMS) (patent pending), was constructed and tested. CF-IMS is a light-weight, low cost instrument that can analyze the composition of the gas phase continuously and with high mobility resolution. In this paper, we report the theory behind CF-IMS and measurements with a low resolution prototype. Reduced mobility of acetone, benzene, and pyridine at 473.15K and 101.3kPa were measured to be 2.35×10−4, 2.32×10−4, and 2.18×10−4, m2V−1s−1, respectively, in agreement with linear IMS measurements. CF-IMS could be used to analyze gas phase compounds or volatile particle phase compounds when used in conjunction with appropriate preconditioners.

Analysis of gas phase compounds in chemical vapor deposition of carbon from light hydrocarbons

Product distributions in the pyrolysis of ethylene, acetylene, and propylene are studied to obtain an experimental database for a detailed kinetic modeling of gas phase reactions in chemical vapor deposition of carbon from these light hydrocarbons. Experiments were performed with a vertical flow reactor at 900 °C and pressures from 2 to 15 kPa. Gas phase components were analyzed by both on-line and off-line gas chromatography. More than 40 compounds from hydrogen to coronene were identified and quantitatively determined as a function of the residence time varied up to 1.6 s. Product recoveries were generally more than 90%. Analysis of the kinetics of the conversion of the hydrocarbons resulted in global reaction orders of 1.2 (ethylene), 2.7 (acetylene), and 1.5 (propylene). First order dehydrogenation reactions and third order trimerization reactions leading to benzene are decisive reactions for ethylene and acetylene, respectively. Conversion of propylene should also be based on two simultaneous reactions, a first order dissociation reaction, and second order reactions such as bimolecular reaction of propylene resulting an allyl and a propyl radical. These insights should be useful to develop a reaction mechanism based on elementary reactions in forthcoming studies.

The estimation of reaction enthalpy for complex molecules using Benson groups

Estimation methods developed over years by S. W. Benson and co-workers for calculation the thermodynamic properties of organic compounds in the gas phase are applied to a pharmaceutical real process with all type of non-idealities. The different strategies used to calculate the reaction enthalpy of a chemical process, in the absence of data for complex molecules, using the Benson group additivity method are presented and also compared with the experimental value of reaction enthalpy obtained using reaction calorimetry (Mettler-Toledo, RC1®). We demonstrate that there are some strategies that can be followed to obtain a good estimation of the reaction enthalpy in order to begin the safety assessment of a chemical reaction. This work is part of an industrial project [1] in which the main objective was the risk assessment of chemical real and complex processes using the commonly available tools for the SMEs (with limited resources).

An Intensive Study of the Size and Composition of Submicron Atmospheric Aerosols at a Rural Site in Ontario, Canada

Atmospheric sampling was conducted at a rural site near Egbert, about 70 km north of Toronto, Ontario, Canada from March 27 to May 8, 2003 to characterize the physical and chemical properties of the ambient aerosol in near real-time. The instrumentation included a tapered element oscillating microbalance (TEOM), an ultrafine condensation particle counter (UCPC), a scanning mobility particle sizer (SMPS), an aerodynamic particle sizer (APS), an aerosol mass spectrometer (AMS), and a particulate nitrate monitor (R&P 8400N) for aerosol measurements. Gas-phase non-methane hydrocarbon compounds (NMHCs) were measured by gas chromatograph-flame ionization detection (GC-FID). Filter samples were also collected for analysis of inorganic ions by ion chromatography (IC). Aerosol properties varied considerably depending upon meteorological conditions and airmass histories. For example, urban and industrial emissions advected from the south strongly influenced the site occasionally, resulting in higher particulate mas...

Schmücke hill cap cloud and valley stations aerosol characterisation during FEBUKO (II): Organic compounds

An extensive speciation of organic compounds was conducted during the FEBUKO cloud experiments in autumn 2001 and 2002. Three measurement sites were chosen at the Schmücke mountain in the Thüringer Wald region, Germany, which allowed to characterise air masses chemically before, during, and after their passage of a hill cap cloud. Concentrations of 33 organic carbonyl compounds, 5 monocarboxylic acids (MCAs), and 10 dicarboxylic acids (DCAs) are reported for different atmospheric phases at the three sites. Some of them were determined for the first time in cloud water. The concentration levels of the compounds were usually low, consistent with the rural sampling region. The identified fraction of dissolved organic carbon in the cloud water was 17.3%, 14.7%, and 10.1%, on average, for three independent cloud events. For the gas phase compounds the phase partitioning between liquid phase and interstitial gas phase inside the cloud was determined and compared to the theoretically expected values considering thermodynamic equilibrium conditions (Henry's law). For relatively polar organic carbonyl compounds (with a high Henry constant and a high effective water solubility), the ratio of measured to calculated liquid phase fractions was close to 1 (0.6–3.4). For the more hydrophobic compounds, however, a significant liquid phase supersaturation with respect to the gas phase concentrations was observed (ratios of 45–912). For the MCAs, only small deviations from Henry's law were determined, comparable to the ones of the polar carbonyl compounds. The scavenging efficiency of the particulate DCAs inside of the cloud was close to 100%. Concentrations of both particulate and gas phase organic compounds were usually lower at the downwind site than at the upwind site. This was most likely due to physical sink processes during the passage of the air parcel over the forested Schmücke mountain.

DFT investigation of sites of protonation of antitumor of 2‐(4‐aminophenyl)benzazoles in the gas phase and in solution

AbstractThe proton affinity on each of the possible sites in the antitumor 2‐(4‐aminophenyl)benzazoles has been calculated at the B3LYP/6‐311G** level of theory in the gas phase and in solution. The N3‐site of protonation is found to be strongly favored over the NH2‐site for the studied compounds both in gas phase and in solution. The stability of N3‐protonated species is explained by the resonance interaction of the NH2‐group with the heterocyclic ring. The potential energy surface (PES) for the protonation process was studied at the density functional theory (DFT)/B3LYP/6‐311++G** level of theory. Solvent effects on the PES were also examined using two models: Onsager self‐consistent field and polarizable continuum model (PCM). © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Interface formation during the yttrium oxide deposition on Si by pulsed liquid-injection plasma enhanced metal-organic chemical vapor deposition

In this article, we investigate the main mechanisms of interfacial SiO2 and silicate formation during yttrium oxide deposition on Si substrates by plasma-enhanced metal-organic chemical vapor deposition using a pulsed-liquid injection delivery source. The precursor supplier system is based on a sequential injection of Y-precursor diluted in an organic solvent. A detailed study of interface thickness and chemical nature is carried out combining angle-resolved x-ray photoelectron spectroscopy, transmission electron microscopy, and electron energy loss spectroscopy. We found that the flow rate of injected reactive species, controlled by the injection frequency, has a strong effect on the plasma gas phase and plays a key role in the SiO2 and silicate formation. For a 1Hz injection frequency deposition, a silicate layer is formed on a thick SiO2 interface [Si∕SiO2(∼3.6nm)∕SixOyYz], whereas deposition at 5Hz induces an oxidized yttrium layer with an interfacial layer composed of a SiO2 and Y-silicate mixture [Si∕SiO2+SixOyYz(∼2nm)∕YxOyCz]. To understand the actual SiO2 origin, the effect of the oxygen plasma on the silicon oxidation was investigated. According to our results, the silicon oxidation by the oxygen O* species from the plasma is strongly enhanced by the presence of organic compounds in the plasma gas phase from reactions between the solvent molecule and the oxygen. This reaction is mostly favored at a low solvent flow rate, which can explain the thicker SiO2 layer observed for the 1Hz sample compared to the 5Hz. When introducing yttrium precursor in addition to the solvent, a Y-based silicate is formed via consumption of the SiO2 by yttrium. The silicate formation is enhanced when a large quantity of SiO2 is available, which is the case for the 1Hz sample. According to this study, a high flow of reactive species is preferred to reduce the interface layer thickness.

Characterization of PM2.5 and selected gas-phase compounds at multiple indoor and outdoor sites in Mira Loma, California

Fine particulate matter (PM2.5) and gas-phase carbonyls are categories of atmospheric pollutants that have components known to adversely affect human health.This work describes the chemical characterization of PM 2.5 and 13 carbonyl compounds measured inside 20 residences and 7 schoolrooms in Mira Loma, western Riverside County, California.Median PM 2.5 concentrations were 32.2 and 13.2m gm � 3 , while median total carbonyl concentrations were 50.8 and 62.9m gm � 3 inside the residences and schoolrooms, respectively.Organic carbon was typically the largest contributor to indoor PM2.5 concentrations, while formaldehyde, acetaldehyde and acetone were the largest contributors to gas-phase carbonyl concentrations.Indoor/outdoor ratios for PM 2.5 were greater for residences than for schoolrooms, while the reverse was true for these ratios for gas-phase carbonyls.These results are likely due to effective PM2.5 removal by filtration on the HVAC and the presence of more significant indoor carbonyl sources within the schoolrooms.Regression analysis of indoor and outdoor pollutant concentrations showed that for PM 2.5, sulfate and nitrate were the best- and worst-correlated species, respectively.This suggests that nitrate is a poor tracer for outdoor-to-indoor PM2.5 transfer.In addition, no significant correlations were observed for any of the carbonyl compounds measured.This further suggests the presence of indoor carbonyl sources inside the schoolrooms, and that indoor air quality especially in terms of carbonyl concentrations may be substantially poorer than outdoor air quality. r 2004 Elsevier Ltd.All rights reserved.

Chemical characterization of outdoor PM2.5 and gas-phase compounds in Mira Loma, California

Outdoor fine particulate matter (PM2.5) andgas-phase compound s were investigatedin Mira Loma, a semi-rural community in southern California, between September 2001 andJanuary 2002. Outdoor PM 2.5 concentrations for the study duration averaged 41.8m gm � 3 , with nitrate andorganic carbon being the major contributors ( � 26% each). Higher PM2.5 concentrations were observed during the first half of the study relative to the second half, corresponding with actinic flux calculations. Gas-phase ammonia concentrations were 6–7 times greater than nitric acid concentrations, while formaldehyde and acetaldehyde concentrations were consistent with Air Resources Board results. Use of a back trajectory model together with PM2.5 chemical composition data showed distinct differences in nitrate andtrace element concentrations for back trajectories originating from Los Angeles andOrange counties versus those originating from Nevada. Source apportionment using a chemical mass balance model helped demonstrate that the total contribution of secondary aerosol (56%) was greater than the total primary vehicular exhaust contribution to PM2.5 by a factor of 5. These results highlight the importance of region-wide secondary sources to the local air quality in this semi-rural area. r 2004 Elsevier Ltd. All rights reserved.

Characterization of urban and rural organic particulate in the Lower Fraser Valley using two Aerodyne Aerosol Mass Spectrometers

Two Aerodyne AerosolMass Spectrometers (AMS) were depl oyed at three sites representing urban, semi-ruraland rural areas during the Pacific 2001 experiment in the Lower Fraser Valley (LFV), British Columbia, Canada in August 2001. The AMS provides on-line quantitative measurements of the size and chemical composition of the non-refractory fraction of submicron aerosol particles. A significant accumulation mode with a peak around 400–500 nm was observed at all sites that was principally composed of sulphate, organics, ammonium and some nitrate. Another significant mode with a peak below 200 nm was also observed at the urban site and when urban plumes affected the other sites. This paper focuses on the variability of the organic particulate composition and size distribution as a function of location and photochemical activity with a particular emphasis on the urban and rural areas. The small organic mode at the urban site was well correlated with gas phase CO, 1,3-butadiene, benzene and toluene with Pearson’s r values of 0.76, 0.71, 0.79 and 0.69, respectively, suggesting that combustion-related emissions are likely to be the main source of the small organic mode at this site. The mass spectra of the urban organic particulate are similar to those of internal combustion engine lubricating oil, and of diesel exhaust aerosol particles, implying that they were composed of a mixture of n-alkanes, branched alkanes, cycloalkanes, and aromatics. In contrast, organic particulate at the rural site was dominated by shorter chain oxidized organic compounds. Correlations between the two organic modes and gas phase compounds at the ruralsite indicated that a significant part of the smal lmode originated from combustion sources, while the large accumulation organic mode appeared to be the result of photochemical processing. Processing

Langmuir–Blodgett Films as Efficient Modifiers of Piezoelectric Sensors

Piezoelectric microweighing is a promising highlysensitive method for quantification of compounds ingaseous and liquid phases; however, its low selectivitysharply restricts the scope of applicability of thismethod in analytical chemistry [1, 2]. The key tech-nique for increasing the selectivity is deposition of sor-bents on the electrodes of the piezoelectric resonator. Mostoften, polymers are used to modify the electrodes [2].Modern procedures for application of the modifieronto the resonator surface (immersion into a solution,spraying, coating, etc.) suffer from various drawbacks.The films obtained in this way have poor adhesion, aninhomogeneous surface, uncontrollable thickness, andlow stability, resulting in poor reproducibility of theresults. All these drawbacks influence the analyticalcharacteristics of piezoelectric sensors [3, 4].We propose using the Langmuir–Blodgett (LB)technology, which involves repeated transfer of mono-molecular layers from the surface of a liquid subphaseonto a solid substrate, for the formation of the sensitivelayer of the piezoelectric resonator [5]. The mostimportant advantages of sensor layers created by meansof the LB technique are as follows:(i) high uniformity of the film combined withmutual orientation of the molecules and functionalgroups composing the film;(ii) the possibility of controlling the film thicknessto an accuracy of a single molecule;(iii) a high ratio of the active surface area of themolecular layers to the film volume;(iv) similarity of the microheterogeneous medium inthe film to the active sites of enzymes and cell mem-branes;(v) the possibility of determining the optimum num-ber of monolayers that ensures the highest analyticaleffect (signal intensity);(vi) the possibility of varying the chemical nature ofthe film by varying the nature of the amphiphile or bycreating mixed monolayers.For the formation of Langmuir–Blodgett films, var-ious amphiphilic compounds were used, namely,arachic acid, which is a traditional compound for thistechnique, and specially prepared alkylatedcalix[4]resorcinarene (CRA) and β -cyclodextrin (CD)[6], which are receptor molecules able to provide addi-tional selectivity through host–guest interaction.The formation of monolayers of amphiphilic sub-stances and their transfer onto the surface of piezoelec-tric resonators (AT-cut, 8 MHz) were carried out on anupdated UNM-2 setup (NIOPIK, Russia). To prepare amonolayer, an amphiphilic substance in a volatileorganic solvent immiscible with water was poured ontothe surface of a liquid subphase (doubly distilledwater). Then the system was held for 20 min; duringthis period, the solvent completely evaporated and themolecules of the amphiphilic substance spread uni-formly over the water surface.The optimal parameters for application of the Lang-muir–Blodgett films were chosen using π –A isothermsthat reflect the sequence of phase transitions takingplace in the monolayer upon compression. The pressurefor the monolayer transfer from the liquid subphasesurface onto the solid substrate was chosen on the basisof the required structural ordering of the film. By suc-cessive transfer of monolayers onto the piezoelectricresonator surface, the thickness of the coating was con-trolled to an accuracy of a single molecule.It was found that the dependence of the frequency ofthe piezoelectric resonator on the number of appliedmonolayers is linear for all the amphiphiles studied,which is indicative of high quality of the resulting films(Fig. 1). The high quality of films is also confirmed byinvariability of the transfer coefficients of the monolay-ers, which are close to unity.