Separation of polar and non-polar analytes using dimethyl sulfoxide-modified subcritical water

Separations using methanol–water or acetonitrile–water mixtures at different temperatures have been well investigated in reversed-phase liquid chromatography. However, reversed-phase separation with dimethyl sulfoxide (DMSO)–water mixtures is much less studied. In this work, separations of polyhydroxybenzenes, phenol derivatives, benzene, toluene, ethylbenzene, and xylenes (BTEX), and polycyclic aromatic hydrocarbons (PAHs) with DMSO-modified subcritical water were performed at several temperatures to evaluate the effect of temperature on the elution strength of DMSO–water mixtures. The column efficiency obtained by using DMSO-modified subcritical water was also studied. Finally, the resolution of ethylbenzene and p-xylene was investigated.     

Determination of benzene, toluene, ethylbenzene and xylenes in air by solid phase micro-extraction/gas chromatography/mass spectrometry

The aim of the study was to analyse BTEX compounds (benzene, toluene, ethylbenzene, xylenes) in air by solid phase micro-extraction/gas chromatography/mass spectrometry (SPME/GC/MS), and this article presents the features of the calibration method proposed. Examples of real-world air analysis are given. Standard gaseous mixtures of BTEX in air were generated by dynamic dilution. SPME sampling was carried out under non-equilibrium conditions using a Carboxen/PDMS fibre exposed for 30 min to standard gas mixtures or to ambient air. The behaviour of the analytical response was studied from 0 to 65 g/m³ by adding increasing amounts of BTEX to the air matrix. Detection limits range from 0.05 to 0.1 g/m³ for benzene, depending on the fibre. Inter-fibre relative standard deviations (reproducibility) are larger than 18%, although the repeatability for an individual fibre is better than 10%. Therefore, each fibre should be considered to be a particular sampling device, and characterised individually depending on the required accuracy. Sampling indoor and outdoor air by SPME appears to be a suitable short-delay diagnostic method for volatile organic compounds, taking advantage of short sampling time and simplicity.     

Rapid Removal of Organics and Oil Spills from Waters Using Silicone Rubber “Sponges”

We have developed a simple, robust, and efficient technology utilizing cheap and recoverable materials based on commercially available silicone elastomer networks for removing organic solvents and crude oil from waters. Hydrophobic and oleophilic properties of silicone elastomers endow poly(dimethyl siloxane) (PDMS) with the capacity to absorb a large variety of organics, including benzene (B), toluene (T), ethylbenzene (E), and xylene (X), commonly referred to as BTEX, and also crude oils, while at the same time enabling the organic “sponges” to float on waters, which facilitates straightforward handling. We developed a method for generating PDMS particles with variable sizes (ranging from hundreds nanometers to few millimeters) by drop-wise depositing siloxane/cross-linker mixtures into warm water, a process which leads to the cross-linking of the PDMS components. We have tested the capability of the PDMS particles to remove toluene and benzene from water. We also performed similar experiments by utilizing PDMS sheets. In both instances we observed a rapid sorption of the organic phase into PDMS; the amount of absorbed organic solvent depended on the concentration in water and the total mass (volume) of PDMS and did not depend on the geometry of the PDMS “sponge.” In addition, we have examined the uptake of toluene and benzene from toluene/benzene (T/B) mixtures dissolved in water. Our results indicate that the amount of benzene absorbed from the T/B mixtures into PDMS increases relative to the uptake from pure benzene/water solutions. This behavior is associated with toluene acting as a “surfactant” that effectively replaces the more unfavorable PDMS/B contacts with less costly T/B ones. Finally, a simple experiment demonstrates qualitatively that PDMS is also capable of removing crude oils from oil-contaminated waters.     

Volatile organic compounds in an urban environment: a comparison among Belgium,Vietnam and Ethiopia

The effects of urban and indoor air pollution on human health are a major environmental concern for all, but not much has been researched in the developing world. Specifically, quantitative data on the occurrence of volatile organic compounds (VOCs) – main contributors to air pollution – in Asia and Africa are scarce compared to the availability of data in the developed world. This paper presents one of the first studies focusing on the analysis and occurrence of VOCs in Vietnam and Ethiopia, which constitutes part of the novelty of this work. A spectrum of 34 VOCs was measured at eight different urban sites in Ghent (Belgium), Hanoi (Vietnam), Jimma and Addis Ababa (Ethiopia) during three sampling campaigns from September 2008 to September 2010. Sampling was done in an active way by means of sorbent tubes filled with Tenax TA. The analysis was done by TD-GC-MS using internal standard calibration. Data were interpreted and compared in terms of (i) individual, subgroup and total VOCs concentration (TVOCs), (ii) indoor-to-outdoor (I/O) concentration ratios, (iii) source identification by diagnostic ratio and/or correlation coefficients, and (iv) ozone formation potential (OFP) at outdoor sites based on up-to-date maximum incremental reactivity (MIR). I/O concentration ratios varied between 0.2 and 30, with big differences noticed with respect to the type of VOC(s) considered and the type of outdoor sampling location. The highest TVOC concentrations were measured in street samples with maximum values of 54?µg/m³ in Ghent, 507?µg/m³ in Hanoi and 318?µg/m³ in Addis Ababa illustrating the large difference in ambient air quality levels. This is also reflected in the arithmetic mean OFP values (µg/m³) of 82, 1308 and 596 in Ghent, Hanoi and Addis Ababa, respectively. Results of this study could be helpful to support formulation of national policy with regard to ambient air quality.     

Ultrasound irradiation effect on morphological and adsorptive properties of a nanoscale 3D Zn-coordination polymer and derived oxide

In this work, Zn-based coordination polymer [Zn₂(1,3-bdc)bzim₂]_n was successfully synthesized by the sonochemical method using a 13 mm probe-type ultrasound operating at 20 kHz and amplitudes of 30, 40 and 50% corresponding to an acoustic power of 5.5, 8.6, and 10.3 W, respectively. Additionally, a sample was prepared by the slow-diffusion method for comparison. The samples were characterized by FTIR, PXRD, SEM, and BET techniques. The influence of the time and sonication amplitude on the yield of the reaction, crystallite size, and morphology were also studied. It was found that the sonochemical method provided the desired product in 83.9% within 20 min of sonication using the highest level of sonication amplitude. Moreover, this approach resulted in regular, controlled morphology, smaller particles, and higher surface area of the Zn-sample and derived oxide, than the slow diffusion method. The samples prepared by different methodologies were tested for the adsorption of BTEX (benzene, toluene, ethylbenzene, and xylenes) components in six different systems, and the uptakes were quantified by ¹³C NMR spectroscopy. Both samples showed excellent adsorption of benzene, 119.8 mmol/g, and 88.1 mmol/g, for the coordination polymers prepared via the sonochemical and slow-diffusion methods, respectively, corresponding to 63.9%, and 46.9%. These results are in agreement with the non-polar surface of these samples.     

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 .     

Comparative analysis of bias in the collection of airborne pollutants: Tests on major aromatic VOC using three types of sorbent-based methods

This study was undertaken to establish one of the most reliable sampling methods and to precisely evaluate the bias involved in the collection of airborne pollutant samples. For the purpose of our study, we investigated the performance of three different types of sampling techniques by measuring major aromatic volatile organic compounds (VOC) in outdoor air; the target analytes specifically include benzene, toluene, ethylbenzene, and xylene (commonly called BTEX). As the first step of our approach, we designed and developed a multi-channel sampling system consisting of a six-port mass flow controller (SJU-MFC) system. Because this system allowed the collection of up to six replicate samples, our measurement results were analyzed and screened statistically for the derivation of high-quality BTEX data. The feasibility of this sampling system was further tested through a comparison with concurrent measurement data sets obtained by two additional, but independent, sampling techniques: (1) automatic continuous sampler (ACS) and (2) on-line GC (O-GC) system. Based on the data sets collected concurrently by three different sampling methods, we attempted to evaluate the compatibility of sampling techniques. Although the results obtained by SJU-MFC system were not statistically different from those of the O-GC system, they were moderately distinguishable from those of ACS. Such patterns were seen consistently, when examined by correlation analysis. The overall results of our study thus generally point out that the compatibility of data sets, when the proper caution is taken, improve significantly among different sampling methodologies.     

Preparation and application of the titania sol-gel coated anodized aluminum fibers for headspace solid phase microextraction of aromatic hydrocarbons from water samples

A novel titania sol-gel coating, including tetrabutyl orthototitanat (TBOT) as initial alkoxide, triethanolamine (TEA) as stabilizer, nitric acid as acid catalyst, and polyethylene glycol (PEG, 6000) as binder was prepared for the first time on an anodized aluminium wire and subsequently applied to headspace solid phase microextraction (HS-SPME) of benzene, toluene, ethylbenzene and xylenes (BTEX) with gas chromatography flame ionization detection (GC-FID). The analytical characteristics of the proposed porous titania sol-gel derived TBOT/PEG/TEA (41.6:16.0:42.4) fiber were comparable with reported fibers. The extraction temperature, extraction time, effect of salt addition, desorption temperature and desorption time were optimized. Under the optimized conditions and for all BTEX components, the linearity was from 20 to 800 μg L⁻¹, the RSD was below 8.2% and limit of detections (LODs) were between 5.4 and 14.8 μg L⁻¹. The recovery values were from 86.7% to 94.2% in water samples. The proposed HS-SPME-GC-FID method was successfully applied for the analysis of BTEX compounds from petrochemical wastewater samples.     

Quantitative Determination of BTEX and Total Aromatic Compounds in Gasoline by Comprehensive Two-Dimensional Gas Chromatography (GC×GC)

Comprehensive two-dimensional gas chromatography (GC×GC) has been applied to the quantitative analysis of benzene, toluene, ethylbenzene, xylenes (BTEX), and all heavier aromatic compounds in gasoline. The two-dimensional chromatographic separation used volatility selection on the first-dimension column and polarity selection on the second-dimension column. In the resulting GC×GC chromatogram, aromatic species were resolved from other compound classes. Moreover, structurally related aromatics were grouped in a manner that facilitated identification and integration. The response of a flame ionization detector to each major aromatic group in gasoline was calibrated using internal standards. Quantitation produced results directly comparable with ASTM standard methods. The present GC×GC method can be expanded to analyze other gasoline components.