Fast Determination of Monocyclic Aromatic Hydrocarbons in Ambient Air Using a Portable Gas Chromatography–Photoionization Detector

Many air sampling methods are time consuming and require complex pre-treatment steps. Gas chromatography–photoionization detector (GC–PID) is a rapid method for sampling and analysis. However, although it has been used in a number of studies, its operating conditions and performance parameters have not been optimized systematically. In this study, a GC–PID method for analysis of monocyclic aromatic hydrocarbons in gas samples without pre-concentration or enrichment was developed and optimized. This GC–PID can perform both online and off-line analysis. In online analysis, the sample was pumped directly into a Teflon sample loop (pumped online injection), which resulted in minimal loss of sample. The optimum parameters were as follows: 30-s pumping time, 10 mL min^?1 of carrier gas flow rate, and 40 °C oven temperature. GC–PID was applied to analysis of benzene, toluene and xylene. The calibration curves showed good linearity for online analysis. The results obtained by GC–PID were accurate and reliable, with all the correlation coefficients ≥0.9972 and all the relative standard deviations <3%. A mixture of benzene, toluene, and o-, m-, and p-xylenes was separated satisfactorily in 10 min, except for m- and p-xylene. The performance of the portable GC–PID was compared with that of an ATD–GC–FID for quantification of benzene, toluene and xylene in calibration gas samples, and benzene, toluene, ethylbenzene, and the o-, m-, and p-xylenes in outdoor ambient air. The results indicated that GC–PID with pumped online injection was stable and accurate for analysis of these monocyclic aromatic hydrocarbons.     

A Mixture of Phospho-, Vanadium-, and Molybdo-Heteropolyacids as a Promising Cathode Redox-Mediator for Hybrid Hydrogen–Air Fuel Cells

Russian Journal of Electrochemistry - Hydrogen–air fuel cell is one of the promising types of chemical power sources, it has a variety of applications. However, utilization of the cathodic...     

Molecular Orientation of a Nematic Liquid Crystal Induced by Mixing with Tetraalkylcalix[4]resorcinarenes at the Air–Water Interface

O-Octacarboxymethoxylated tetraalkylcalix[4]resorcinareanes (CRA-CMs) formed stable monolayers on a water surface, whereas their -A isotherms were affected by the length of the alkyl residues. A double-layered structuring was observed for CRA-CM having four undecyl substituents (11CRA-CM) by compression, though CRA-CM with four eicosyl residues formed a stable monomolecular film. 11CRA-CM possessed the ability to form a host–guest monolayer film with liquid crystalline 4,4'-dihexylazobenzene at the air/water interface, leading to perpendicular orientation of C6Azo. The host–guest mixed monolayers displayed a double-layered structuring by compression.     

A New HPLC Method to Determine Carbonyl Compounds in Air

In this paper,a new HPLC method was established to determine the earbonyl compounds in air.As the absorbent,2,4-dinitrophenylhydrazint(2,4-DNPH)reaeted with earbonyls specifieally,which form the corresponding 2,4-dinitrophenylhydrazones,then analyzed by HPLC.The chromatographic conditions,the recovery rate,stability of samples,reagent blank,sampling efficiency were all studied systematically.The results showed that this established method had high sensitivity and good selectivity compared with other analytical methods,and it can detemine ten earbonyl compounds in air in 26 min simultancously.     

Synthesis of Calix[4]arene Derivatives Containing a Nucleobase and their Interaction with Complementary Nucleosides at the Air–Water Interface

Amphiphilic calix[4]arene derivatives with a nucleobase on the lower rim have been synthesized in good yields by the condensation of calix[4]arenediamine {5,11,17,23-tetra-tert-butyl-25,27-bis(2-aminoethoxy)-26,28-dihydroxycalix[4]arene} with uracilo-N-acetic acid, thymino-N-acetic acid and adenino-N-propionic acid in the presence of CDI in DMF. Monolayers of the amphiphilic calix[4]arene-nucleobase derivatives on the surface of pure water, the aqueous subphases containing complementary nucleosides, were studied by film balance measurement and relaxation experiments. LB films deposited from all subphases were investigated by UV spectra and FT-IR spectroscopy. All the results indicate that the interaction between the nucleobases in the headgroup of amphiphilic p-tert-butylcalix[4]arene derivatives and the complementary nucleosides in the subphase takes place through multiple hydrogen bonding and the nucleosides can be transferred to solid substrates along with their monolayers.     

Isolation and Characterization of Naphthenic Acids from a Metal Naphthenate Deposit: Molecular Properties at Oil‐Water and Air‐Water Interfaces

Naphthenic acids from a West African metal naphthenate deposit have been isolated and characterized by infrared (IR), nuclear magnetic resonance (NMR), and Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS). The sample has been shown to comprise a narrow group of 4‐protic naphthenic acids of molecular weight ～1230 Da. The determined mass of 1230.0627 Da suggests a compound with the elemental composition C₈₀H₁₄₂O₈. The NMR data show no sign of carbon‐carbon multiple bonds. Hence, the elemental composition indicates the presence of six saturated hydrocarbon rings. The naphthenic acids have proved to be highly oil‐water (o/w) interfacially active. On elevation of the pH from 5.6 to 9.0, interfacial activity increases gradually due to a higher degree of dissociation of the carboxylic groups. At pH 9.0, the interfacial tension (IFT) between water and toluene‐hexadecane (1–9 vol.) is lowered by ～40 mN/m at concentrations of only 0.0050–0.010 mM naphthenic acid. The time rate of decrease of the IFT (dγ/dt) is also concentration‐dependent, and a well‐defined IFT is attained at long observation periods.

The C₈₀ naphthenic acids form relatively unstable Langmuir monolayers. The stability decreases further with increasing pH as more monomers become dissociated and dissolve into the aqueous phase. The stability is altered upon addition of calcium ions into the subphase due to formation of calcium naphthenate at the surface. In the undissociated state, the acids have a molecular area of ～160 Å²/molecule in the noninteracting region. The high area reflects an extended molecular structure comprising four carboxylic head groups, which are likely to be separated by hydrocarbon chains.     

In situ Observation of the Photochromism in the Langmuir Monolayer of a Non—typical Amphiphilic Spiropyran Derivative at the Air／Water Interface

In situ photochromic process in the monolayer of aphotochromic spiropyran derivative without long alkyl chain,was investigated.The photochromism at the air/water interface under differnet surface pressures was studied by surface pressure-area isotherms,surface pressure-time curves,area-time curves and Brewster angle microscopy.Both forms of the compound were found to form monolayers at the air/water interface althouhg it does not have long alkyl chain.A large area expansion in the monolayer corresponding to a zreo^th order reaction was found at the initial stage of the UV light irradiation.A series of dynamic investigations revealed that at high pressure after phase transition in the monolayer,the surface pressure changes greatly umder alternative irradiation of UV and visible light.An obvious morphological change accompanying with the photochromism was observed in situ.     

Adsorption Kinetics of Alkyl Polyglucoside at the Air—Solution Interface

The air-solution equilibrium tension γe and dynamic surface tension γt,of nonionic surfactant alkyl polyglucoside have been studied. γe was measured by the Wilhelmy method with Rruess K12 tensiometer. The CMC and the surface excesses T were determined from the surface tension vs. concentration curve. The γt decays were measured in the range 0.2-20s using a maximum bubble pressure instrument and analyzed with the Ward and Tordai equation.     

Kinetics of the Thermal Decomposition of Magnesium Salicylate Powder in Air

IntroductionThe chelate complexes of salicylic acid with rareearth and alkali earth ions have attracted considerableattention because of their special antibacterial proper-ties[1—3].The study of the thermal degradation of metalsalicylates is of major int…     

GIS-based Analysis of Main Air Pollutants of Changchun City in Summer

To gain a better understanding of the characteristics of air pollution of Changchun city, P. R. China, in summer, the analytical methods of geographical information system（GIS） and statistical analysis software SPSS were applied to the analysis of the monitored concentrations of SO2 , NO2, and O3 in July of 2002 to 2004 in Changchun city. The results obtained show that the average hourly O3 concentrations in July 2002 and 2004 were higher than the firstlevel hourly standard of China. At the same time, the dynamic distribution of the 03 concentration and the relationship between the concentration of 03 and that of NOx were studied. The air quality evaluation result of Changchun city indicates that the southwest of this city was heavily polluted during the monitored period.     

MOF-Mediated Fabrication of a Porous 3D Superstructure of Carbon Nanosheets Decorated with Ultrafine Cobalt Phosphide Nanoparticles for Efficient Electrocatalysis and Zinc–Air Batteries

Superstructures have attracted great interest owing to their potential applications. Herein, we report the first scalable preparation of a porous nickel-foam-templated superstructure of carbon nanosheets decorated with ultrafine cobalt phosphide nanoparticles. Uniform two-dimensional (2D) Co-metal organic framework (MOF) nanosheets (Co-MNS) grow on nickel foam, followed by a MOF-mediated tandem (carbonization/phosphidation) pyrolysis. The resulting superstructure has a porous 3D interconnected network with well-arranged 2D carbon nanosheets on it, in which ultrafine cobalt phosphide nanoparticles are tightly immobilized. A single piece of this superstructure can be directly used as a self-supported electrode for electrocatalysis without any binders. This “one-piece” porous superstructure with excellent mass transport and electron transport properties, and catalytically active cobalt phosphide nanoparticles with ultrasmall size (3–4 nm), shows excellent trifunctional electrocatalytic activities for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR), achieving great performances in water splitting and Zn–air batteries.     

Cleaning of Air Streams from Organic Pollutants by Plasma–Catalytic Oxidation

Oxidative removal of a mixture of chlorinated ethylenes and aromaticcompounds in air in a pulse corona discharge reactor combined with metaloxide catalyst downstream was investigated in a field experiment. Dischargewas initiated by high-voltage pulses of 70–75 kV peak voltage and200 ns risetime. A flow of 60 m³/h was treated at11–12 Wh/m³ with catalyst held at 110°C at a spacevelocity of 6000 h^–1. Removal rates of 70–90% havebeen found with input concentrations in the parts per million and thesubparts per million range. No partially oxidized hydrocarbons could bedetected in cleaned air. A closed carbon balance was confirmed underlaboratory test conditions.     

Dynamic Study of Gemini Surfactant and Single-chain Surfactant at Air／Water Interface

Molecular dynamics (MD) simulation are used to study the properties of gemini surfactant of ethyl-α,ω-bis(dodecyldimethylammonium bromide) (C12C2C12) and dodecyl-trimethylammonium bromide (DTAB) at the air/water interface, respectively. In the two systems,t he surfactant concentrations are both 28 wt.%, and other conditions are also the same. After reaching the thermodynamic equilibrium, the concentration profiles, the radial distributions functions (RDF) and the mean squared displacement (MSD) are investigated. The results reveal that the surface activity of C12C2C12 surfactant is higher than DTAB surfactant.     

Air Pollution Investigation in Vitória Metropolitan Region, ES, Brazil

The application of Mössbauer spectroscopy, X-ray diffractometry, thermogravimetric analysis and PIXE in the characterization of the particulate matter in atmospheric aerosols in Metropolitan Region of Vitória (MRV), Brazil have been investigated. The main sources of particulate matter, natural, industrial and antropogenic from human activities, have been studied to identify its contribution in the atmospheric particles. During the years 1995 to 1999 samples of total suspended particles (TSP, Ø 100 m) were collected from four points within MRV. The inhalable particles (PM₁₀ Ø 10 m) and sedimented particles (SP) were also collected from the same region. A receptor modeling was used for the identification of the source of particulate matter in the collected urban aerosol.     

Multimedia Analysis of Radon in 10 mL of Air for in-Laboratory Quality Assurance

A new, simple, reliable and self-consistent procedure has been developed to produce, handle and measure radon in 10mL of air in the three media air, water and charcoal simultaneously. Equal and low activities of radon (200Bq, 4ag) are transferred with a 10mL gas syringe from a 3.8L natural, harmless and constant radon source to three receivers: a 48L Peli case with outdoor air, an 0.5L bottle with tap water, and a 22mL tube with activated charcoal. Concentrations, i.e. activities in the three media are measured with different methods providing independent results. Hence, in-laboratory cross-method calibration and traceability to a certified standard is available for radon in air and in water for the first time and with minimum effort.     

Analysis of Phthalate Esters in Air,Soil and Plants in Plastic Film Greenhouse

The phthalate esters such as MDP,DEP,BDP and DEHP in air,soil and plant smples in plastic film greenhouse were clean up with fine silica gel column and determined with HPLC.It was found that the concentrations of PEs in ari and soil samples in plastic film greenhouse are much higher than those of contrast samples. But concentration of PEs in plants in plastic film greenhouse are not remarkably affected by the pollution of air and soil.     

Voltammetric Probing of Molecular Assemblies of Ubiquinone-10 at the Air–Water Interfaces

The redox properties of ubiquinone 10 (UQ10) placed at the air–water interface were studied using the horizontal touching method with a thin mercury film (TMFE) working electrode and cyclic voltammetry. Changes of pH of the subphase affected the formal potential of the ubiquinone/ubiquinol system exhibiting the participation of protons in the overall reduction of UQ10. The protonation of the semiquinone transition product was found to be the rate determining step. This explains the dependence of the rate constant value on pH. The highest values of rate constants were found at pH over 13. Under these conditions the mechanism of the process is different. The concentration of protons is small, and the availability of the counter ions (i.e., K⁺) becomes crucial for the kinetics of reduction. Their role is to neutralize the negative charge of the redox group following its reduction. The logarithm of rate constants was found to decrease linearly with the increase of surface concentration of ubiquinone. This reflects the influence of intermolecular interactions in the monolayer on the kinetics of the electrode process.     

Is Chromatography a Science, a Process, a Method, or a Scientific Discipline?

In the controversy over an article entitled Chromatography as a Scientific Discipline by V.G. Berezkin, it was pointed out that the subdivision of chromatographic processes into sorption–sieve chromatography and field nonsorption chromatography is inadmissible. It was demonstrated that all chromatographic processes, including flow fractionation in a transverse force field, are in principle two-phase (or polyphase) processes. It was illustrated that a longitudinal field in a flow cannot introduce a chromatographic component into the system. An additional definition of chromatography as a phenomenon was proposed on the basis of key points revealed by Professor Berezkin.     

Air–water interfacial behavior of amphiphilic peptide analogs of synthetic chloride ion transporters

A family of heptapeptide-based chloride transporters (called synthetic anion transporters, SATs) were designed to insert into phospholipid membrane bilayers and form pores. Many of these compounds have proved to be chloride selective transporters. The transporters were designed to incorporate hydrophilic heptapeptides that could serves as headgroups and hydrocarbon tails that could serve as hydrophobic membrane anchors. Insertion of the SAT molecules into a bilayer requires approach to and insertion at the aqueous-membrane surface. The studies reported here were conducted to model and understand this process by studying SAT behavior at the air–water interface. A Langmuir trough was used to obtain surface pressure–area isotherm data. These data for amphiphilic SATs were augmented by Brewster angle microscopy (BAM), molecular modeling, and calculations of the hydrophobicity parameter log P. The analyses showed that the heptapeptide (hydrophilic) module of the SAT molecule rested on the water surface while the dialkyl (hydrophobic) tails oriented themselves in the air, perpendicular to the water surface. Brewster angle microscopy visually confirmed a high order of molecular organization. Results from these studies are consistent with the previously proposed mechanism of SAT membrane insertion and pore formation.