Determination of BTEX in Water Samples with an SPME Hollow Fiber Coated Copper Wire

A piece of copper wire coated with a polypropylene hollow fiber membrane was used as an SPME fiber and its efficiency for extraction of BTEX compounds from the headspace of water samples prior to GC analysis was evaluated. Under optimum extraction conditions, limits of detection for benzene, toluene, ethylbenzene, m-p-xylene, and o-xylene were found to be 0.11, 0.22, 0.26, 0.37, and 0.26 μg L^?1, respectively. Low detection limits, wide linear dynamic ranges, good reproducibility (RSD% <4), high fiber capacity and higher mechanical durability are some of the most important advantages of the new fiber.     

Analysis of gasoline contaminated water samples by means of dopant-assisted atmospheric pressure photoionization differential ion mobility spectrometry

In this study the influence of aromatic dopant benzene on the sensitivity of GC-APPI-DMS to gasoline related aromatic compounds was investigated. This influence was investigated on example of four gasolin related fingerprints (toluene, ethylbenzene, o-xylene, and 1,2,4-trimethylbenzene), which were found in high relative abundance in the water-soluble gasoline fraction. The analysis of calibration curves slopes demonstrats that the GC-APPI-DMS sensitivity to gasoline fingerprints can be improved by up to seven times when benzene concentration in nitrogen carrier gas is less than 10 ppm_v/v. The estimated detection limits (S/N?=?3) for the analyzed in this study compounds were found to be within the range of 33–105 μg L^?1 at benzene concentration in the carrier gas of 2.27 ppm_v/v (10 μL injection volume). These limits of detection may be reduced (at the cost of lower resolution) using the larger injection volumes. For example, increase of injection volume to 100 μL at benzene concentration in the carrier gas of 2.27 ppm_v/v leads to reduction of LOD values for toluene, ethylbenzene, and o-xylene to 11.1, 13.3, and 5.3 μg L^?1, respectively.     

Comparison of SPE-TD-GC-FID with UPLC-PDA and GC-MS Methods for Analysis of Benzene, Toluene and Xylene Isomers in Solid-Liquid Mixing Paints

Three methods were developed for analysis of benzene, toluene, p-xylene, m-xylene and o-xylene (BTX) in a solid-liquid mixing paint. These methods were based on solid phase extraction-thermal desorption-gas chromatography with a flame ionization detector (SPE-TD-GC-FID), ultra performance liquid chromatography-photodiode array detector (UPLC-PDA) and gas chromatography-mass spectrometry (GC-MS). At their optimum conditions of operation, the developed methods were compared in terms of recovery, sensitivity, selectivity and universality. Although the time required for GC-MS analysis was shorter than for GC-FID and UPLC-PDA, it offered relatively poorer recoveries and suffered from matrix interferences. All of the mentioned methods were proven to be ideal for the analysis of targeted analytes; SPE-TD-GC-FID was particularly fit for the determination of trace level BTX residues present in the complex matrix. As one of the sample pretreatment techniques, the novel SPE also showed some selectivity towards BTX and was found to be superior to the conventional SPE.     

Desorption of BTEX from activated charcoal using accelerated solvent extraction: evaluation of occupational exposures

A procedure for the determination of benzene, toluene, ethylbenzene and o-xylene, m-xylene and p-xylene (BTEX) in occupational environments is proposed. These compounds are extracted from activated charcoal using accelerated solvent extraction. Operational parameters are optimized and quantitative recovery is obtained using acetonitrile as the extraction solvent and 1-mL extraction cells, a preheat time of 2 min, a temperature of 160 °C, a pressure of 1,500 psi, a static period of 5 min, a flush volume of 110%, two cycles and a purge time of 90 s. Determination of BTEX compounds is carried out by gas chromatography using a flame ionization detector. The recoveries, obtained for a confidence level of 95%, are 91 ± 4, 100 ± 3, 104 ± 2, 93 ± 4, 99 ± 2 and 99 ± 2% for benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene, respectively. The detection limits are 0.5 μg for benzene, 0.7 μg for toluene and 1.0 μg for the other compounds. The proposed procedure has been applied to real samples collected in several workplaces, like a microbiology laboratory, an analytical chemistry laboratory, a printer’s, a car repair shop and a petrol station. From the results obtained, it can be concluded that the occupational exposures determined are always acceptable because they are lower than the tenth part of the recommended exposure limits (VLA-ED and VLA-EC).     

Vapour–liquid equilibria of butyl acetate with aromatic hydrocarbons at 298.15 K

Vapour pressures of butyl acetate?+?benzene or toluene or o- or m- or p-xylene were measured by static method at 298.15?±?0.01?K over the entire composition range. The activity coefficients and excess molar Gibb's free energies of mixing (G ^E) for these binary mixtures were calculated by fitting vapour pressure data to the Redlich–Kister equation using Barker's method of minimizing the residual pressure. The G ^E values for the binary mixtures containing benzene are positive; while these are negative for toluene, ortho, meta and para xylene system over the whole composition range. The G ^E values of an equimolar mixture for these systems vary in the order: benzene?>?m-xylene?>?o-xylene?>?p-xylene?>?toluene     

Infrared spectroscopic and gravimetric studies on the cyclopropylaminemetal(II) tetracyanonickellate(II) host–aromatic guest systems

The host complexes M(Cyclopropylamine)₂Ni(CN)₄ (M = Co or Cd) have been prepared in powder form. The spectral data suggest that the structures of these compounds are similar to those of the Hofmann-type hosts. The absorption and the liberation processes of the aromatic guests (benzene, toluene, 1,2-dichlorobenzene, o-xylene, m-xylene and p-xylene) in these hosts have been examined at room temperature by gravimetric and spectroscopic measurements. The desorption of the benzene guest against time has been measured. The host structures do not change on inclusion and liberation of the guest. The host compounds have been suggested as sorbents for isomeric separations.     

Sorption of trifluoromethane in activated carbon

Sorption isotherms for trifluoromethane (R-23) in activated carbon have been measured at ca. 298 and 323 K using a gravimetric microbalance. High-resolution TEM images of the activated carbon show a very uniform microstructure with no evidence of any contaminants. The adsorption in the activated carbon reaches about 22.8 mol kg^?1 at 2.0 MPa and 298 K or 17.6 mol kg^?1 at 2.0 MPa and 323 K. Three different adsorption models (Langmuir, multi-site Langmuir, and BET equations) have been used to analyze the activated carbon sorption data, with a particular interest in the heat of adsorption (?ΔH). The heat of adsorption for R-23 in the activated carbon was about 29.78 ± 0.04 kJ mol^?1 based on the multi-site Langmuir model and is within the range of typical physical adsorption. According to the IUPAC classification, the activated carbon exhibits Type I adsorption behavior and was completely reversible. Compared with our previous work for the sorption of R-23 in zeolites (5A (Ca,Na-A), 13X (Na-X), Na,K-LSX, Na-Y, K,H-Y, Rb,Na-Y) and ionic liquids ([omim][TFES] and [emim][Tf₂N]) the activated carbon had the highest adsorption capacity. The adsorption process in the activated carbon also took less time than in the zeolites or the ionic liquids to reach thermodynamic equilibrium.     

Excess volumes of mixing of 1,2-dichloroethane and aromatic hydrocarbons

Excess volumes of mixing, V^E, for binary mixtures of 1,2-dichloroethane with benzene, toluene, o^?, m^?, and p-xylenes have been determined at 308.15 K over the complete composition range. V^E is positive for all these mixtures and varies in the order m-xylene >o-xylene >p-xylene > benzene > toluene. The experimental data have been analyzed in terms of the Prigogine's average potential cell model coupled with Balescu's theory. The calculated V^E values do not agree with the corresponding experimental values.     

Hydrogen-bonding-driven self-assembly nonporous adaptive crystals for the separation of benzene from BTX and cyclohexane

Benzene is a volatile organic compound that can seriously harm human health, while it can serve as a precursor to produce chemicals of more complex structures in chemical industry. Capturing benzene using adsorbents is of great importance for human health, when the separation of hydrocarbons including benzene from crude oil was referred to as one of the “seven chemical separations to change the world”. In this work, we reported the efficient and selective separation of benzene from BTX and cyclohexane by hydrogen bonding self-assembly nonporous adaptive crystals AdaOH for the first time under mild and user-friendly conditions. Separation of benzene and cyclohexane (v/v = 1:1) can be achieved by AdaOH with a purity of benzene up to 96.8%. Separation of BTX (v/v; benzene:toluene:o-xylene:m-xylene:p-xylene= 1:1:1:1:1) can be achieved by AdaOH with a purity of benzene increased from 20% to 82.9%. Our results suggest that separation of benzene using the activated AdaOH as a non-porous adaptive crystal for selectively and efficiently capturing benzene can solve the challenge in separation of benzene from other chemicals such as cyclohexane in chemical industry, and can be helpful for removal of benzene that is released from the vehicles to air. The advantages of commercially availability, easy preparation, high separation efficiency and selectivity for benzene might endow this material with enormous potential for practical uses in areas like petrochemical industry.     

Isothermal Phase Equilibrium Studies on the Binary Mixtures of some Alkylbenzenes

Abstract

The gas chromatographic method proposed by us for simple and accurate measurement of isothermal phase equilibria has been applied to the binary mixtures formed by alkylbenzenes amongst themselves. Results on the binary mixtures of: benzene - toluene, toluene + o-xylene, toluene + p-xylene, toluene + ethylbenzene, ethylbenzene + o-xylene and ethylbenzene + p-xylene are presented in this paper. The present measurements on benzene + toluene system at 40°C are in good agreement with the isothermal phase equilibrium data available in the literature.     

Comparative study on lanthanum(III) sorption onto Lewatit TP 207 and Lewatit TP 260

Batch experiments are carried out for the sorption of La(III) onto commercial macroporous resins containing iminodiacetic (Lewatit TP 207) and aminomethylphosphonic acid groups (Lewatit TP 260). The operating variables studied are initial La(III) concentration, pH, temperature and contact time. Since the extraction kinetics were fast, with a mixture of 0.1 g of resin and 5 mL of lanthanum ions 0.5 × 10^?3 mol L^?1 solution, extraction equilibrium was reached within 30 min of mixing. The optimum pH values level for quantitative sorption were between 1.5 and 4.6 with Lewatit 207 and about 5.2 with Lewatit TP 260. The sorption capacities of Lewatit TP 207 and Lewatit TP 260 resins are 114.7 and 106.7 mg g^?1, respectively. Adsorption equilibrium data were calculated for Langmuir and Freundlich isotherms. It was found that the sorption of La(III) on Lewatit TP 207 was better suited to the Langmuir adsorption model while Freundlich adsorption model fitted better sorption on Lewatit TP 260. Thermodynamics data leads to endothermic and spontaneous process. ΔG° decreases with increasing temperature indicating that sorption process of La(III) on both Lewatit TP 207 and Lewatit TP 260 was more favored at high temperature.     

Preparation of a Carbon-Coated SPME Fiber and Application to the Analysis of BTEX and Halocarbons in Water

A carbon-coated fiber for solid-phase microextraction (SPME) has been prepared from powdered activated carbon (PAC) and a fused-silica fiber. Scanning electron microscopy of the coating revealed the carbon particles were uniformly distributed on the surface of the fiber substrate. Efficient extraction of BTEX (benzene, toluene, ethylbenzene, p-xylene, and o-xylene) and halocarbons (chloroform, trichloroethylene, and carbon tetrachloride), with short extraction and desorption times, was achieved by use of the coated fiber. The maximum working temperature of the coated fiber was 300 °C and the lifetime was over 140 desorption operations at 260 °C. Limits of quantification (LOQ) of the SPME method for the eight analytes ranged from 0.01 to 0.94 μg L⁻¹, and relative standard deviations (RSD) were below 7.2% (n=6). Recoveries were 87.9–113.4% when the method was applied to the analysis of BTEX and the halocarbons in real aqueous samples. An erratum to this article is available at .     

Monitoring 60Co activity for the characterization of the sorption process of Co2+ ions in municipal activated sludge

In large volumes produced activated sludges from wastewater treatment plants (WWTPs) with low concentrations of heavy metals can be utilized as agricultural fertilizers and soil conditioners. Increased contents of toxic xenobiotics are limiting factors that affect the utilization of these heterogeneous wastes. The main aim of our paper was to show the utilization of dried activated sludge (DAS) from municipal WWTP as potential Co²⁺ ions sorbent i.e. for non-agricultural purposes. The radio indicator method by radionuclide ⁶⁰Co and γ-spectrometry for characterization DAS sorption properties was used. DAS soluble and solid fractions were characterized by biochemical, ETAAS and CEC analysis. The sorption of Co²⁺ ions by DAS was rapid process and equilibrium was reached within 2 h. Sorption capacity of DAS (Q) increased with the initial concentration of CoCl₂ in the range from 100 to 4,000 μmol l^?1, reaching 20 and 160 μmol g^?1. Obtained Q values were depent on pH value from 2.0 to 8.0. The maximum sorption capacity (Q _max) of DAS at pH 6 calculated from mathematical model of Langmuir adsorption isotherm was 175 ± 9 μmol g^?1. FT-IR analyses showed the crucial role of carboxyl functional groups of DAS surfaces on cobalt uptake. For confirmation ion-exchange mechanism in sorption process of Co²⁺ ions by DAS scanning electron microscopy and EDX analysis were used.     

Determination of BTEX Compounds in Solid–Liquid Mixing Paint Using the Combination of Solid Phase Extraction,Thermal Desorption and GC-FID

A novel method was developed and validated for determination of benzene, toluene, p-xylene, m-xylene, o-xylene (BTEX) in a solid–liquid mixing matrix. It makes use of solid phase extraction and thermal desorption (SPE-TD), followed by gas chromatographic flame ionization detector analysis (GC-FID). The trapped BTEX can be measured directly after thermal desorption onto the stainless-steel packed chromatographic column. The effect of tailing area of solvent was removed with the use of SPE-TD technique, and the result shows good reproducibility with very little matrix dependency. The study also supports that the lifetime of the Tenax adsorption tube could be extended over 150 desorption operation at 200 °C, which enables performing excellent stability and reproducibility of BTEX analysis.

     

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.     

Rate constants for the gas-phase reactions of the OH radical with a series of aromatic hydrocarbons at 296 ± 2 K

Using a relative rate method, rate constants have been determined at 296 ± 2 K for the gas-phase reactions of the OH radical with toluene, the xylenes, and the trimethylbenzenes. Using the recommended literature rate constant for the reaction of OH radicals with propene of (2.66 ± 0.40) × 10^?11 cm³ molecule^?1 s^?1, the following rate constants (in units of 10^?12 cm³ molecule^?1 s^?1) were obtained: toluene, 5.48 ± 0.84; o-xylene, 12.2 ± 1.9; m-xylene, 23.0 ± 3.5; p-xylene, 13.0 ± 2.0; 1,2,3-trimethylbenzene, 32.7 ± 5.3; 1,2,4-trimethylbenzene, 32.5 ± 5.0; and 1,3,5-trimethylbenzene, 57.5 ± 9.2. These data are compared with the literature values.     

Analysis of BTEX and chlorinated solvents in meconium by headspace-solid-phase microextraction gas chromatography coupled with mass spectrometry

Meconium is the earliest stool of newborns, and is a complex matrix that reflects the degree of exposure of the fetus to xenobiotics. To investigate fetal exposure to volatile organic compounds, an analytical method was developed to identify and quantify BTEX (benzene, toluene, ethylbenzene, and o,m,p-xylene) and two chlorinated solvents (trichloroethylene and tetrachloroethylene) in meconium. Headspace-solid-phase microextraction coupled with gas chromatography–mass spectrometry was selected because it is simple, sensitive, can be automated, and requires no extensive sample preparation. Several extraction variables were optimized (fiber type, incubation time, temperature of fiber, and use of salt). Because meconium is a complex matrix, quantification by SPME was considered carefully because of potential interference, for example competitive adsorption. Calibration in water was compared with calibration in meconium using external and internal methods (with isotope-labeled compounds). In meconium, limits of quantification were determined to be in the range 0.064–0.096 ng g^?1 for the investigated compounds. All target compounds were determined in “real-case” meconium samples.     

Study of the gadolinium sorption on the C100 ion-exchange resin for the development of the antineutrino detector targets

Adsorption of the gadolinium from H₂O and HCl solutions on the ion-exchange resin C100 is investigated. The experiments were carried out by varying the acidity of the liquid phase, the amount of sorbent, and the temperature. The maximal sorption of the ions Gd³⁺ is observed from the solution 0–0.2 M HCl under optimal conditions, the sorption reaches more than 99.5%. Sorption of Gd³⁺ on C100 from H₂O solution occurs most intensively during the first 3 min then for 30 min the system smoothly comes to equilibrium. The maximal sorption capacity of the resin C100 amounted to 1.2 ± 0.1 mmol g^?1. The thermodynamic parameters of sorption: ΔG = ? 24.20 kJ mol^?1, ΔS = ? 90.27 J mol^?1 K^?1, ?H = ? 50.93 kJ mol^?1 were evaluated. It is shown that the sorption of gadolinium on the ion-exchange resin C100 is described by models of kinetically pseudo-first and pseudo-second order. It is established that the Gd³⁺ sorption on the C100 resin is reversible second order chemical reaction.     

Synthesis and identification of bromofullerenes C70Br8 and C70Br10 and their solubility in some aromatic solvents

Bromofullerenes C₇₀Br₈ and C₇₀Br₁₀ were synthesized and identified by electronic absorption and infrared spectroscopy. Their solubility in aromatic solvents (benzene, toluene, o-xylene, and o-dichlorobenzene) was studied in the temperature range from 20 to 60°C.     

Adsorption of UO2 2+ on poly(N,N-diethylacrylamide-co-acrylic acid): effects of pH, ionic strength, initial uranyl concentration, and temperature

We prepared poly(N,N-diethylacrylamide-co-acrylic acid) (P(DEA-co-AA)) microgels which could efficiently remove UO₂ ²⁺ from aqueous solutions. In this study, the effect of adsorption parameters such as pH value, adsorbent dose, shaking time, and temperature has investigated. It is found that the pseudo-second-order model is more suitable for our experiment. The adsorption kinetic data indicated that the chemical adsorption was the swiftness processes, the adsorption equilibrium could be achieved within 30 min. And there are very good correlation coefficients of linearized equations for Langmuir isotherm model, which indicated that the sorption isotherm of the hydrogel for UO₂ ²⁺ can be fitted to the Langmuir isotherm model. The adsorption process was spontaneous (?G ⁰ < 0) and exothermic (?H ⁰ < 0). The adsorbed UO₂ ²⁺ can be desorbed effectively by 0.1 M HNO₃ and the adsorption capacity is not significantly reduced after five cycles. Present study suggests that this P(DEA-co-AA) can be used as a potential adsorbent for sorption UO₂ ²⁺ and also provide a simple, fast separation method for removal of UO₂ ²⁺ ions from aqueous solution.