Chemiluminescence determination of chlorinated volatile organic compounds by conversion on nanometer TiO2

A novel method based on conversion of chlorinated volatile organic compounds (CVOCs) to chlorine using a new type of column packed with nanometer TiO2 coupled with chemiluminescence (CL) has been developed for determination of them in workplace air. CVOCs are converted to chlorine by nanometer TiO2 at 220 degrees C. The Cl2 that is produced is selectively enriched on the column and subsequently released from the column at 600 degrees C. The Cl2 that is released is determined using a postcolumn CL detector. The CL intensity was linear with CCl4 in the range of 0.1-380 ppm, and the detection limit was 40 ppb (S/N = 3). Higher sensitivity could be acquired by using a larger volume of enrichment A similar procedure could be used for the determination of other CVOCs. CL intensities of CH2Cl2, CHCl3, and CCl4 at the same concentration increased in the order CH2Cl2 < CHCl3 < CCl4. The method has been successfully applied to the determination of CCl4 in workplace air, where 0.15-150 ppm CCl4 would be detected. The possible mechanism for the long lifetime of the column packed with nanometer TiO2 was tested using Raman spectrometer, X-ray powder diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The results showed that the column packed with nanometer TiO2 could be operated in the reversible mode for determination of CVOCs under the present conditions. The method would be potentially applied to the analysis of other chlorinated compounds in environment, such as persistent organic pollutants.     

Disturbance of laser-induced-fluorescence measurements of NO in methane-air flames containing chlorinated species by photochemical effects induced by 225-nm-laser excitation

Laser-induced fluorescence measurements of NO in CH(4)-air flames seeded with CH(3)Cl and CH(2)Cl(2) are described. The measurements are perturbed by strong photochemical effects characterized by UV emissions. The contribution of these background emissions is taken into account on the basis of an on-line-off-line resonance procedure. First results indicate an important increase of NO in the presence of chlorinated species. Background emissions observed in the range 220-260 nm and at 278 nm are ascribed, respectively, to electronically excited HCl and CCl photofragments. It is shown that C(2)H(3)Cl and CHCl(2) species are responsible for the formation of HCl and CCl, respectively, and a photolytic mechanism for formation of the photofragments is proposed.     

Adsorption dynamics of chlorinated hydrocarbons from multi-component aqueous solution onto activated carbon

The results and a numerical simulation of studies on dynamics of the adsorption from seven-component aqueous solution of light chlorinated hydrocarbons on activated carbon have been presented. Aqueous solution of 1,2-dichloroethane (12DCE), 1,1,2,2-tetrachloroethane (S-TET), chloroform (CHCl(3)), carbon tetrachloride (CCl(4)), 1,1-dichloroethene (VDC), perchloroethene (PER) and 1,1,2-trichloroethene (TRI) was used. Concentrations of chlorohydrocarbons were similar as in wastewater from vinyl chloride plant. A cell model that incorporates the diffusion through a laminar layer of liquid around a particle was used to describe the experimental results. The applied calculation methods, which take kinetics into account, allows to well describe a phenomenon of dynamic adsorption. Mean relative deviations between the experimental and calculated values amounted 17%. The breakthrough curves become steeper along with an increase of the bed height. A consistency of the experimental results with those calculated indicates for a negligible contribution of the axial diffusion on the dynamic adsorption process of light chlorinated hydrocarbons from aqueous solution under the hydrodynamic conditions corresponding to the Reynolds number equal to 1.3. Determined optimal bed height for waste linear flow rate-15 cm/min is in the range 80-120 cm.     

Photocatalytic decomposition of CCl4 on Zr-MCM-41

Photocatalytic decomposition of CCl4 (80 mg L(-1) in H2O) effected by Zr-MCM-41 (Zr incorporated in the amorphous wall of MCM-41) has been studied in the present work. Experimentally, photocatalytic decomposition of CCl4 on Zr-MCM-41 was enhanced by about 1.96 times over that on ZrO2. Photocatalytic decomposition of CCl4 may proceed via a two-electron transfer process that yields mainly CHCl3, Cl- and H2. Since little C2Cl2, C2Cl6 or CH2Cl2 was found, it is unlikely that CHCl3 involved in the secondary photocatalytic degradation process. In addition, photocatalytic splitting of H2O on Zr-MCM-41 was also enhanced. The yield of H2 was 6.5 mmol(gZrO2)(-1). About 68% of this hydrogen (6.5 mmol(gZrO2)(-1)) was consumed in the photocatalytic decomposition of CCl4.     

High temperature oxidation of C2Cl4/CH4 mixtures

Experiments on high temperature oxidation of multi-chlorinated hydrocarbons, tetrachloroethylene (C2Cl4), with hydrocarbon fuels, CH4, were performed in a 15 mm i.d. tubular flow reactor. Temperatures ranged from 700 to 850 degrees C, with the average residence time in the range from 0.3 to 1.5s. Three equivalence ratios, phi=0.87 (fuel-lean (FL)), phi=1 (stoichiometry (S)), and phi=1.3 (fuel-rich (FR)), were studied. The global Arrhenius equations for the decomposition of C(2)Cl(4) for each reactant set ratio are: k(lean)=5.77 x 10(15) exp(-30447/RT), k(stoi)=5.15 x 10(15) exp(-30421/RT), and k(rich)=6.32 x 10(14) exp(-28879/RT). The important reactions for destruction of parent C2Cl4 include: C2Cl4 --> C2Cl3 + Cl, C2Cl4 + H--> C2Cl3 + HCl and C2Cl4 + H --> C2HCl3 + Cl. The resulting reactant loss, and intermediate and final product profiles were determined. C2HCl3, C2Cl2, CO, CO2 and HCl are the major products for the reaction of C2Cl4/CH4/O2 mixtures for these three reaction systems. Minor intermediates include C2H3Cl, C2HCl, COCl2, CH3CHCl2, C2H4, C2H6, CCl2CHCH3 , trans-CHClCHCl, cis-CHClCHCl, trans-ClHC=CClCH(3), C6H6, and Cl2. The experimental data showed that as the oxygen concentration increased, the temperature needed to detect the resulting products decreased.     

Dielectric barrier discharge-induced chemiluminescence: potential application as GC detector

Atmospheric pressure dielectric barrier discharge (DBD) plasma can be used to split low molecular weight organic compounds, and the DBD-split/excited species can be swept into luminol solution to induce chemiluminescence (CL) emission. Based on this observation, a novel optical detector was proposed and preliminarily tested as a potential gas chromatographic (GC) detector in this work. The advantages of this new type of detector include the following: direct detection, fast response, high sensitivity, versatility (sensitive to a broad range of volatile organic compounds), simple and easy instrumentation, compactness (3.0 mm i.d. x 4.0 mm o.d. x 20 mm length of the DBD device), and low power (less than 5 W). Twelve volatile organic compounds, including methanol, ethanol, propanol, formaldehyde, acetaldehyde, benzene, dichloromethane, trichloromethane, tetrachloromethane, tetrahydrofuran, carbon bisulfide, and ethyl ether, were tested with this detector, and each of them produced a large signal. It was found that the CL signal was proportional to the analyte concentration and affected by the DBD parameters. Under the optimized experimental conditions, the limits of detection down to the tens of nanogram level were achieved for methanol, ethanol, propanol, formaldehyde, and acetaldehyde. It was then preliminarily tested as a GC detector for the separation of formaldehyde, ethanol, and propanol. This is the new application of DBD in analytical chemistry, and CL was for the first time generated in this way. The new detector can be a potential GC detector suitable for a wide range of volatile organic compounds.     

Microplasma source based on a dielectric barrier discharge for the determination of mercury by atomic emission spectrometry

A low-power, atmospheric-pressure microplasma source based on a dielectric barrier discharge (DBD) has been developed for use in atomic emission spectrometry. The small plasma (0.6 mm x 1 mm x 10 mm) is generated within a glass cell by using electrodes that do not contact the plasma. Powered by an inexpensive ozone generator, the discharge ignites spontaneously, can be easily sustained in Ar or He at gas flow rates ranging from 5 to 200 mL min(-1), and requires less than 1 W of power. The effect of operating parameters such as plasma gas identity, plasma gas flow rate, and residual water vapor on the DBD source performance has been investigated. The plasma can be operated without removal of residual water vapor, permitting it to be directly coupled with cold vapor generation sample introduction. The spectral background of the source is quite clean in the range from 200 to 260 nm with low continuum and structured components. The DBD source has been applied to the determination of Hg by continuous-flow, cold vapor generation and offers detection limits from 14 (He-DBD) to 43 pg mL(-1) (Ar-DBD) without removal of the residual moisture. The use of flow injection with the He-DBD permits measurement of Hg with a 7.2 pg limit of detection, and with repetitive injections having an RSD of <2% for a 10 ng mL(-1) standard.     

Sensitive in situ detection of chlorinated hydrocarbons in gas mixtures

We detect chlorinated hydrocarbons (CHC's) in gas mixtures by dissociating the CHC's with a 193-nm laser and measuring the subsequent concentration of the CCl fragmentation by means of laser-induced fluorescence. Sub-ppm detection, where ppm indicates parts in 10(6), is achieved for C(2)H(5)Cl with a 10-mm(3) measurement volume and integration over 50 laser shots. Every other CHC tested is also detectable, with the same or better detection limits. The CCl forms promptly during the fragmentation laser pulse through unimolecular dissociation of the parent CHC's. The technique should be a useful diagnostic for CHC incineration systems.     

Optical restriction of plasma emission light for nanometric sampling depth and depth profiling of multilayered metal samples

Improvement in depth profiling capabilities of laser-induced breakdown spectrometry (LIBS) for multilayered samples has been attempted. For this purpose, in a typical LIBS experiment, an optical restriction consisting of a pinhole placed between the dichroic mirror and the collecting lenses has been used. This new optical approach allows observing only the light emission coming from the central region of the plume. The microplasma was created on the sample by a pulsed Nd:YAG laser operating at 1064 nm with a homogeneous distribution of energy across the beam. Light emitted by the microplasma was detected with an intensified charge-coupled device (iCCD) multichannel detector. The effect of pinhole diameter and the delay time influence on depth analysis have been assessed. An ablation range of only a few nanometers per pulse has been achieved. Depth profiles of various metals (Cr, Ni, Cu) from multilayered samples have been generated by LIBS and depth resolution at different delay times using various pinhole diameters have been calculated and compared.     

Thermal decomposition of 1,1-dichloroethene diluted in hydrogen

The reaction of 1,1-dichloroethene in an excess hydrogen environment with a Cl/H ratio of 0.04 was investigated in an isothermal tubular reactor at a total pressure of 1 atm with residence time of 0.3-2.0 s between 575 and 900 degrees C. C(2)H(3)Cl and HCl are the primary reaction products from the decomposition of CH(2)CCl(2) while the formation of C(2)H(4), C(2)H(2), C(2)H(6), and CH(4) increases as reaction time or temperature increases.Modeling used a detailed chemical mechanism involving 59 species and 202 elementary reactions; the results were compared with experimental observations. Sensitivity analyses were also performed to rank the significance of each reaction in the mechanism. The optimal reaction condition for the C(2) hydrocarbons production from the dechlorination of CH(2)CCl(2) in H(2) environment was also determined.     

Device for Raman difference spectroscopy

A new layout of a versatile Raman difference setup is presented. The new device combines the advantages of the rotating cell for exploitation of the resonance Raman enhancement and the high precision of Raman difference spectroscopy together with the multiplex advantages and very high quantum efficiency offered by a CCD detector. While Raman difference spectroscopy is the most accurate method for the detection of very small band shifts, the method requires the strict prevention of any environmental perturbation of one of the two spectra, which are used for the difference spectra calculation. The presented device satisfies this requirement by implementing a double-beam layout, where the simultaneously detected Raman signals of two sample cells are combined within a Y-fiber bundle and imaged together onto the CCD detector. The accuracy of the new apparatus in detecting frequency shifts and minor sample components is greatly increased compared to conventional Raman spectroscopy as shown by studying binary mixtures of CHCl3 and CCl4. Hereby it was possible to resolve a formerly undetected shift of <0.02 cm(-1) of the CCl4 band at 218 cm(-1). The new RDS setup has a very versatile design. The device can take advantage of the high sensitivity and selectivity of the resonance Raman enhancement applying excitation wavelengths from the UV to NIR and can be used for a variety of samples with only minor changes in the optical arrangement. The new device will be of utmost importance for a fast, gentle, sensitive, selective, and precise investigation of biomolecules and their interactions. Some first results are shown concerning the interaction of the antimalarial chloroquine with hematin in a hydrous environment.     

苯乙烯存在下稀土催化合成窄分布高顺式聚丁二烯

采用Nd（P507）3（简称Nd）、氢化二异丁基铝（简称Al）、三氯甲烷（简称Cl）和三氯乙酸乙酯（简称ETCA）催化体系,以环己烷为溶剂,在苯乙烯（St）的存在下,实现丁二烯的选择性聚合。考察了[Al]/[Nd]和[Cl]/[Nd]比、St加入量、聚合温度等对聚合的影响。结果表明,在[Al]/[Nd]比为20、[Cl...     

Surface modification using a commercial triple quadrupole mass spectrometer

We report instrumental modifications to a commercial mass spectrometer that allow surface modification experiments to be performed using low-energy (electronvolt range) mass-selected ion beams. The design of the detector housing allows placement of the surface on the ion optical axis and some distance beyond the off-axis detector. Manipulation of the potentials applied to the final lens, detector housing, conversion dynode, and electron multiplier allow the ions to pass through the detector housing and impinge upon the surface without loss of the normal mode of detector operation. Ex situ analysis of the modified surface is performed using a home-built multisector mass spectrometer. The ability to modify organic thin films is demonstrated by a number of soft landing and surface modification experiments including (i) soft landing of (CH3)2SiNCS+ ions formed from trimethylsilyl isothiocyanate upon a fluorinated self-assembled monolayer (F-SAM) surface, (ii) soft landing and dissociative soft landing of the pseudomolecular cation of triphenylpyrylium tetrafluoroborate, viz. the triphenylpyrylium cation, upon an F-SAM surface, (iii) dissociative soft landing of 35ClCH2(CH3)2SiOSi(CH3)2+ formed from 1,3-bis(chloromethyl)disiloxane upon an F-SAM surface, (iv) surface passivation by reaction of the trimethylsilyl cation, Si(CH3)3+, with a hydroxyl-terminated self-assembled monolayer (OH-SAM), and (v) transhalogenation by reaction of CCl3+ (m/z 119) with an F-SAM surface.     

Atmospheric microplasma jet: spectroscopic database development and analytical results

This paper presents a developed dielectric-barrier-discharge-based "sniffer" that offers unique characteristics not available from other techniques. It is a portable, highly specific, and sensitive detector that operates at atmospheric pressure. It provides both molecular and elemental information on organic and inorganic gases and particulate aerosols. Measurements were made to electrically characterize the plasma and calculate the energy coupled into the plasma. We created a signature database for diverse chemicals based on the atomic and diatomic emission spectrum that serves to classify the compound and ideally recognize it by composition with the optical emission intensity corresponding to concentration. For some operational regimes and species, emission from OH (A(2)Σ(+)-X(2)Π), CH (A(2)Δ-X(2)Π), and often C(2) (d(3)Π(g)-a(3)Π(u); Swan band system) diatomic radicals is produced. Limits of detection extend to parts per billion (ppb) levels for some species such as decane, 2-decanol, and nitrobenzene. Results are presented for differentiation of classes of organic compounds such as alkanes, aromatics, oxygenates, chlorinated, and nitrogen-containing organic compounds.     

Helium discharge detector for quantitation of volatile organohalogen compounds

A helium discharge has been evaluated as an element-selective, gas chromatographic detector for volatile organohalogen compounds. Absolute limits of detection ranged from 3 pg for chloroform to 29 pg for p-dibromobenzene with a linear response of 10(3)-10(4). The relative response of the detector was determined to be based solely on the mass of the halogen species present. This feature allowed for relatively simple quantitation of chlorinated and brominated haloform species in water samples by the addition of a single internal standard for calibration of the halogen response.     

Aqueous heavy metals removal by adsorption on amine-functionalized mesoporous silica

Amino functional mesoporous silica SBA-15 materials have been prepared to develop efficient adsorbents of heavy metals in wastewater. Functionalization with amino groups has been carried out by using two independent methods, grafting and co-condensation. Three organic moieties have been selected to incorporate the active amino sites: aminopropyl (H(2)N-(CH(2))(3)-), [2-aminoethylamino]-propyl (H(2)N-(CH(2))(2)-NH-(CH(2))(3)-) and [(2-aminoethylamino)-ethylamino]-propyl (H(2)N-(CH(2))(2)-NH-(CH(2))(2)-NH-(CH(2))(3)-). Materials have been characterized by XRD, nitrogen sorption measurements and chemical analysis. We have found that all materials preserve the mesoscopic order and exhibit suitable textural properties and nitrogen contents to act as potential adsorbents. Metal removal from aqueous solution has been examined for Cu(II), Ni(II), Pb(II), Cd(II), and Zn(II); adsorption performances of materials prepared by the two functionalization methods have been compared. In addition, copper adsorption process has been thoroughly studied from both kinetic and equilibrium points of view for some selected materials. Aqueous Cu(II) adsorption rates show that the overall process is fast and the time evolution can be successfully reproduced with a pseudo-second-order kinetic model. Whole copper adsorption isotherms have been obtained at 25 degrees C. Significant maximum adsorption capacities have been found with excellent behavior at low concentration.     

Thermodynamic studies of the solvent effects in chromatography on molecularly imprinted polymers. 3. Nature of the organic mobile phase

Experimental isotherm data of the Fmoc-tryptophan (Fmoc-Trp) enantiomers were measured by frontal analysis on a Fmoc-L-Trp imprinted polymer, using different organic mobile phases, in a wide concentration range. The nonlinear regression of the data and the independent calculation of the affinity energy distributions of the two enantiomers allowed the selection of the isotherm model and the determination of the isotherm parameters. The organic solvents studied were acetonitrile (MeCN), methylene chloride, chloroform, and tetrahydrofuran (THF), all in the presence of the same concentration of acetic acid, used as an organic modifier. It was found that the highest overall affinity and enantiomeric selectivity were obtained in MeCN, which is also the solvent used in the polymerization. In the other solvents, the overall affinity decreases with increasing hydrogen-bonding ability of the solvents but not the enantiomer selectivity. In MeCN, three types of adsorption sites coexist for the two enantiomers on the MIP. The highest energy sites for Fmoc-L-Trp in MeCN are inactive in CH(2)Cl(2), CHCl(3), and THF, and only two types of sites were identified in these solvents. Increasing the acetic acid concentration from 0.2 to 0.9 M causes a large decrease in the association constant of the highest energy sites in CH(2)Cl(2), CHCl(3), and THF but not in MeCN. The overall affinity of Fmoc-L-trp in CH(2)Cl(2), CHCl(3), and THF is dominated by adsorption on the lowest energy sites, the most abundant ones. In contrast, in MeCN, the overall affinity of Fmoc-L-Trp is dominated by adsorption on the highest energy sites, the least abundant sites. In CH(2)Cl(2), CHCl(3), and THF, the number of each type of sites increases with decreasing hydrogen-bonding ability of the solvents while the association constant of the corresponding sites does not change significantly.     

Fluorophilic ionophores for potentiometric pH determinations with fluorous membranes of exceptional selectivity

Ionophore-doped sensor membranes exhibit greater selectivities and wider measuring ranges when they are prepared with noncoordinating matrixes. Since fluorous phases are the least polar and least polarizable liquid phases known, a fluorous phase was used for this work as the membrane matrix for a series of ionophore-based sensors to explore the ultimate limit of selectivity. Fluorous pH electrode membranes, each comprised of perfluoroperhydrophenanthrene, sodium tetrakis[3,5-bis(perfluorohexyl)phenyl]borate, and one of four fluorophilic H(+)-selective ionophores were prepared. All the ionophores are highly fluorinated trialkylamines containing three electron withdrawing perfluoroalkyl groups shielded from the central nitrogen by alkyl spacers of varying lengths: [CF(3)(CF(2))(7)(CH(2))(3)](2)[CF(3)(CF(2))(6)CH(2)]N, [CF(3)(CF(2))(7)(CH(2))(3)](2)(CF(3)CH(2))N, [CF(3)(CF(2))(7)(CH(2))(3)](3)N, and [CF(3)(CF(2))(7)(CH(2))(5)](3)N. Their pKa values in the fluorous matrix are as high as 15.4 +/- 0.3, and the corresponding electrodes exhibit logarithmic selectivity coefficients for H(+) over K(+) as low as <-12.8. The pKa and selectivity follow the trends expected from the degree of shielding and the length of the perfluoroalkyl chains of the ionophores. These electrodes are the first fluorous ionophore-based sensors described in the literature. The selectivities of the sensor containing [CF(3)(CF(2))(7)(CH(2))(5)](3)N are not only greater than those of analogous sensors with nonfluorous membranes but were of the same magnitude as the best ionophore-based pH sensors ever reported.     

Strategies for formaldehyde detection in flames and engines using a single-mode Nd:YAG/OPO laser system

This paper presents technical developments for the detection of formaldehyde (CH2O) using laser-induced fluorescence. The easily accessible third harmonic of the Nd:YAG laser at 355 nm was used for excitation of formaldehyde. In order to investigate potential background fluorescence, e.g., from large molecules such as polyaromatic hydrocarbons, special attention was paid to investigating the possibility of scanning the wavelength of a single-mode Nd:YAG laser under the gain profile, approximately 3 cm(-1), on and off resonance. Furthermore, a technique for simultaneous detection of formaldehyde and OH using one laser system is presented. The single-mode Nd: YAG laser at 355 nm in combination with an optical parametric oscillator (OPO) laser tuned to 283 nm was used for simultaneous two-dimensional imaging of both species using one charge-coupled device (CCD) detector equipped with a dual filter image separator. The techniques are demonstrated with measurements in laboratory flames and the combined measurements are also demonstrated in an engine.     

Medusa: a sample preconcentration and GC/MS detector system for in situ measurements of atmospheric trace halocarbons, hydrocarbons, and sulfur compounds

Significant changes have occurred in the anthropogenic emissions of many compounds related to the Kyoto and Montreal Protocols within the past 20 years and many of their atmospheric abundances have responded dramatically. Additionally, there are a number of related natural compounds with underdetermined source or sink budgets. A new instrument, Medusa, was developed to make the high frequency in situ measurements required for the determination of the atmospheric lifetimes and emissions of these compounds. This automated system measures a wide range of halocarbons, hydrocarbons, and sulfur compounds involved in ozone depletion and/or climate forcing, from the very volatile perfluorocarbons (PFCs, e.g., CF(4) and CH(3)CF(3)) and hydrofluorocarbons (HFCs, e.g., CH(3)CF(3)) to the higher-boiling point solvents (such as CH(3)Cl(3) and CCl(2)=CCl(2)) and CHBr(3). A network of Medusa systems worldwide provides 12 in situ ambient air measurements per day of more than 38 compounds of part per trillion mole fractions and precisions up to 0.1% RSD at the five remote field stations operated by the Advanced Global Atmospheric Gases Experiment (AGAGE). This custom system couples gas chromatography/mass spectrometry (GC/MSD) with a novel scheme for cryogen-free low-temperature preconcentration (-165 degrees C) of analytes from 2 L samples in a two-trap process using HayeSep D adsorbent.