Direct screening and confirmation of benzene, toluene, ethylbenzene and xylenes in water

Modeling Bisolute Adsorption of Aromatic Compounds Based on Adsorbed Solution Theories

A large number of organic contaminants are commonly found in industrial and municipal wastewaters. For proper unit design to remove contaminant mixtures by adsorption, multicomponent adsorption equilibrium models are necessary. The present work examined the applicability of Ideal Adsorbed Solution Theory (IAST), a prevailing thermodynamic model, and its derivatives, i.e., Segregated IAST (SIAST) and Real Adsorbed Solution Theory (RAST), to bisolute adsorption of organic compounds onto a hyper-cross-linked polystyrene resin, MN200. Both IAST and SIAST were found to be less accurate in fitting the experimental bisolute adsorption isotherms than RAST. RAST incorporated with an empirical four-parameter equation developed in this work can fit the adsorbed phase activity coefficients, γ_i, better than RAST combined with the Wilson equation or the Nonrandom two-liquid (NRTL) model. Moreover, two polyparameter linear free energy relationships were developed for the adsorption of a number of solutes at low concentrations in the presence of a major contaminant (4-methylphenol or nitrobenzene). Results show that these relationships have a great potential in predicting γ_i of solutes when the adsorbed amounts are dominated by a major contaminant. To the best of our knowledge, this is the first study predicting γ_i for bisolute adsorption based on molecular descriptors. Overall, our findings have proved a major step forward to accurately modeling multisolute adsorption equilibrium.

Fast identification and quantification of BTEX coupling by Raman spectrometry and chemometrics

Monoaromatic hydrocarbons (MAHs) monitoring is of environmental interest since these chemical pollutants are omnipresent.

Response surface modeling of ultrasound-assisted dispersive liquid-liquid microextraction for determination of benzene, toluene and xylenes in water samples: Box-Behnken design

A simple, fast and effective pre-concentration procedure for the extraction of benzene, toluene and xylenes isomers (BTX) was developed using an ultrasound-assisted dispersive liquid-liquid microextraction coupled with gas chromatography-flame ionization detector in water samples. The effects of different experimental parameters in the extraction step including type and volume of extraction and dispersive solvents, ionic strength, extraction time and sample volume were studied using two techniques, namely one-variable-at-a-time and response surface methodology. The results of "one-variable-at-a-time" showed that the ionic strength and extraction time were not significant on the extraction efficiency. Therefore, a three-factor, three-level Box-Behnken experimental design was employed to optimize the BTX extraction. The optimal conditions were determined to be a volume of extraction solvent (chloroform) of 51 μL, volume of dispersive solvent (methanol) of 514 μL and volume of sample of 12 mL. The enrichment factors of 241.2-305.1, the limit of detections of 205-382 ng L(-1) were obtained for the BTX at the optimum conditions. In addition, the relative standard deviations for 50 μg L(-1) of the BTX in the water samples were found to be in the range of 1.9 %-5.7 % (n = 5). The developed procedure was then applied for the extraction and determination of BTX in the water samples.

Rapid screening of polycyclic aromatic hydrocarbons (PAHs) in waters by directly suspended droplet microextraction-microvolume fluorospectrometry

A rapid and simple screening method for polycyclic aromatic hydrocarbons (PAHs) in water samples is proposed. The method is based on the combination of a miniaturized sample preparation approach, namely, directly suspended droplet microextraction (DSDME), and microvolume fluorospectrometry. Benzo[a]pyrene (BaP) was used as the model compound for screening purposes. Under optimal conditions, a detection limit of 0.024 μg L(-1) and an enrichment factor of 159 were obtained for BaP in 5 min. The repeatability, expressed as relative standard deviation (RSD), was 4.9% (n=8). The unreliability region of the screening method was 0.54-0.67 μg L(-1), by using a cut-off value of 0.6 μg L(-1) of BaP. Finally, the proposed method was applied to the in situ achievement of the binary "yes/no" response for PAHs in different water samples and recovery studies were performed at three different levels, with BaP recoveries in the range of 93-104%.

Multivariate statistical study of seasonal variation of BTEX in the surface water of Savitri River

Volatile organic compounds (VOCs) analysis was carried out for the surface water of the Savitri river during the period of June 2005 to June 2007. BTEX compounds (Benzene, Toluene, Xylene & Ethyl benzene) were analyzed by using micro extraction technique (Purge & Trap). Concentrations of these BTEX compounds were ranging from 0.1 to 1.5 ppm during sampling period. Higher concentrations of BTEX were found at sampling location VI. Concentration of ethyl benzene was very low as compare to other compounds. However, the concentration of benzene was very high. Seasonal variations in conc. of BTEX compounds were observed and higher concentration was detected during the summer season. Salting-out effect had given higher quantification values. In PCA and PFA, the component loading for all the variables are positively correlated. Death of fishes was observed in the river that is indication of severe pollution problem.

Enhancing Sensitivity in Headspace-Mass Spectrometric Determination of BTEX in Drinking Water

A way to extract useful chemical information from the volatile profile provided by a headspace-mass spectrometer (HS-MS) is developed in order to improve sensitivity in HS-MS analysis. The methodology is based on the selection of a narrow window in the volatile profile where the signal-to-noise ratio was maximal by combining the data acquisition time and scan rate. To test this approach, benzene, toluene, ethylbenzene, and p-xylene (BTEX) as well as their mixtures were quantified in drinking waters. Individual hydrocarbons were determined between 1 and 30 microg/L (mean RSD, 4.0% for 10 microg/L) while mixtures were quantified at a microgram per liter level by using the partial least-squares multivariate algorithm with a relative standard prediction error of under 3.5%. These results indicate that the method proposed is useful as a sensitive and selective tool for the determination of BTEX and surpasses other reported HS-MS alternatives. In addition, the proposed methodology can be extended to others that insert analytes from a sample directly into a MS, such as membrane introduction mass spectrometry among others.

A rapid, sensitive screening test for polycyclic aromatic hydrocarbons applied to Antarctic water

We describe a rapid, sensitive, fluorescence screening test for polycyclic aromatic hydrocarbons in water samples that avoids more costly time-consuming methods. The screening test works by detecting benzo[a]pyrene. It runs without the need for any pre-concentration step, thus rendering it suitable for routine use in water-quality-control laboratories. The test recognizes contaminated samples rapidly (150 s) and inexpensively with a cut-off level of 10 ng l(-1), which is the value that the European Union and World Health Organization (WHO) have laid down in its assessment of the quality of water for human consumption. This was first ascertained by analysing tap and waste-water samples before studying environmental water samples from the Antarctic region. The reliability of the screening test was 2% false positives and 4% false negatives in 200 samples of tap and waste-water. The applicability was confirmed by the fact that the predictions of the screening test coincided exactly with results obtained with gas chromatography-mass spectrometry assays. We also discuss the polluted Antarctic samples and the possible sources of the contamination involved.

Direct screening and confirmation of priority volatile organic pollutants in drinking water

A screening tool was proposed for the rapid detection of eight priority volatile organic pollutants according to European standards in drinking water. The method is based on the direct coupling of a headspace sampler with a mass spectrometer, using a chromatographic column heated to 175 degrees C as an interface. The water sample was subjected to the headspace extraction process and the volatile fraction was introduced directly into the mass spectrometer, without prior chromatographic separation, achieving low detection limits (0.6-1.2 ng/ml) for all compounds. The mass spectrum resulting from the simultaneous ionization and fragmentation of the mixture of molecules constitutes the volatile profile of each sample. An appropriate chemometric treatment of these signals permitted them to be classified, on the basis of their volatile composition, as contaminated or uncontaminated with respect to the legally established concentration levels for these compounds in drinking water, and providing no false negatives. A conventional confirmation method was carried out to analyze positive water samples by using the same instrumental setup as in the screening method, but using an appropriate temperature program in the chromatographic column to separate, identify and quantify each analyte.

Determination of a wide range of volatile and semivolatile organic compounds in snow by use of solid-phase micro-extraction (SPME)

Quantification and transformation of organic compounds are pivotal in understanding atmospheric processes, because such compounds contribute to the oxidative capacity of the atmosphere and drive climate change. It has recently been recognized that chemical reactions in snow play a role in the production or destruction of photolabile volatile organic compounds (VOC). We present an environmentally friendly method for determination of VOC and semi-VOC in snow collected at three sites-remote, urban, and (sub-)arctic. A solid-phase micro-extraction (SPME) procedure was developed and (semi-)VOC were identified by gas chromatography with mass spectrometric detection (GC-MS). A broad spectrum of (semi-)VOC was found in snow samples, including aldehydes, and aromatic and halogenated compounds. Quantification was performed for 12 aromatic and/or oxygenated compounds frequently observed in snow by use of neat standard solutions. The concentrations detected were between 0.12 (styrene and ethylbenzene) and 316 microg L(-1) (toluene) and limits of detection varied between 0.11 (styrene) and 1.93 microg L(-1) (benzaldehyde). These results indicate that the SPME technique presented is a broad but selective, versatile, solvent-free, ecological, economical, and facile method of analysis for (semi-)VOC in natural snow samples.