Partition Coefficients Of Volatile Organic Compounds Research Articles

Development of an in situ equilibrium polydimethylsiloxane passive sampler for measuring volatile organic compounds in soil vapor

An equilibrium passive sampler made of polydimethylsiloxane (PDMS) fiber was developed to measure volatile organic compounds (VOCs) in soil vapor. Expanded polytetrafluoroethylene (ePTFE) was used to protect PDMS from pollution and direct contact with soil components. For all tested VOCs, equilibrium was reached after 7 days at 5 °C. The equilibrium partition coefficients of VOCs between PDMS, gas, and water were measured at three different temperatures. The analyte concentrations in PDMS exposed to gas and water separately were almost the same, which suggests that Cgas and Cwater in soil pores can be accurately deduced from CPDMS after equilibrium at various temperatures. To evaluate the passive sampler, active sampling measurements were performed simultaneously. Concentrations of VOCs deduced from the passive sampler were consistent with the concentrations measured by active sampling near the 1:1 line. Tests with artificial soils were conducted to observe the effects of soil components on passive sampling. The results suggest that the effect of water saturation can be ignored; in other words, the developed passive sampler can be applied in the vadose zone, which has fluctuating water saturation. With a holder for the sampler made of stainless steel, the developed in situ passive sampler can measure VOCs in contaminated soil vapor. The developed passive sampler was proven to be an alternative for measuring VOCs in soil vapor, which can be helpful for soil risk assessment and for observing the diffusion of VOCs in contaminated sites.

Air pollution: new bio-based ionic liquids absorb both hydrophobic and hydrophilic volatile organic compounds with high efficiency

Emission of volatile organic compounds (VOCs) in the atmosphere is a major health concern for the World Health Organization (WHO). For instance, more than 4 million premature deaths are attributed yearly to outdoor air pollution, thus calling for advanced remediation techniques. Absorption systems using solvents are commonly used to remove air pollutants, yet efficiency is limited by a solvent property, which is either hydrophilic or hydrophobic. As a consequence, classical solvents are not able to capture both hydrophilic and hydrophobic contaminants. Therefore, we synthesized the following ionic liquids from choline chloride and fatty acids: hexylcholinium levulinate, octylcholinium levulinate, hexylcholinium lactate and octylcholinium lactate. Ionic liquids were then tested for absorption of toluene, dichloromethane (CH2Cl2) and methyl ethyl ketone. Ionic liquids were characterized by 1H and 13C NMR, infrared spectroscopy, differential scanning calorimetry and thermal gravimetric analysis, density, viscosity and polarity. Vapor–liquid partition coefficients of VOC were determined for ionic liquids. We found that solvents were able to solubilize both hydrophobic and hydrophilic VOC. Moreover, no saturation was detected up to an initial VOC concentration of 3000 g/m3, whereas classical absorption processes usually involve gas streams containing VOC concentrations up to 1000 g/m3. Moreover, the solvent can be successfully recycled with unchanged capacity during five absorption–desorption cycles. Overall, our solvents appear promising for the treatment of industrial gaseous effluents.

A method to measure the partitioning coefficient of volatile organic compounds in nanoparticles

The partitioning behavior of volatile organic compounds (VOCs) into nanoparticles is less studied compared to those of semivolatile organic compounds (SVOCs) because of the lower concentration of the VOCs that is expected to partition into particles. One challenge in measuring the accurate partition coefficient of VOCs is quantifying their low mass fraction that sorbed on nanoparticles and differentiating them from the high VOC concentrations present in the gas-phase. Systematically characterizing the partitioning coefficient at a specific environmental condition is also difficult when sampling in the field. During field sampling, thermal and non-thermal issues such as sampling artifacts and non-equilibrium conditions because of a dynamic environment often result in considerable variability in the measured partition coefficients. In this study, we developed a bench-scale system that can achieve precise control of the experimental condition (e.g., relative humidity, temperature, and particle composition) and allow us to measure the low concentration of 1,2-dichlorobenzene in the particles. A similar set up can be used to study the low mass fraction of other VOCs partitioning in nanoparticles. The detailed but uncomplicated system setup may assist other researchers that investigate the global fate and transport and health effects of VOCs.•A bench-scale system was built in the laboratory to study the gas-to-particle partitioning•Experimental conditions can be controlled and easily varied•The system enables the systematic study of a single environmental factor on the partitioning process

Dynamic—static Chamber Method for Simultaneous Measurement of the Diffusion and Partition Coefficients of VOCs in Barrier Layers of Building Materials

Barrier layers on the surface of building materials play an important role in reducing the emission of volatile organic compounds (VOCs), but there is little data about their transport properties such as the solid-phase diffusion coefficient (D) and the solid/air partition coefficient (K). This paper develops a dynamic—static chamber (DSC) method for determining the D and K for VOCs in barrier layers. The developed method has the following advantages: (1) it can simultaneously but separately determine D and K for a VOC mixture with controllable concentration in a single test and (2) it requires a relatively shorter experimental time (e.g., less than 1 h for the testing of VOCs in the barrier layers). Using this method, the two key parameters for formaldehyde in three commonly used barrier layers were measured. The uncertainty and sensitivity of the measured parameters were analysed. The results indicated the feasibility of simultaneous estimation of the two parameters (D and K) by the present method. Finally, the impact of the tested barrier layers on VOC emissions from building materials was investigated based on a multilayer mass transfer model. It is found that barrier layers can greatly reduce the indoor VOC concentration. The measured D and K values of barrier layers are useful for predicting VOC emissions from building materials and in the design of low-emission building materials.

An improved extraction method to determine the initial emittable concentration and the partition coefficient of VOCs in dry building materials

Based on the extraction method presented by Smith et al. (2008), this paper proposes an improved method, the multi-emission/flush regression method, to simultaneously determine the initial emittable concentration and the partition coefficient. Compared to the extraction method, the proposed method has the following advantages: (1) it is unnecessary for the target volatile organic compounds (VOCs) to emit completely from the material, thus greatly reducing experimental time; (2) it provides a simpler way to obtain the partition coefficients of VOCs for tested materials and can avoid the measurement uncertainties at low VOC concentrations which often occur during the last few cycles of the extraction method; (3) it does not require grinding the building material into powders thus making this method more convenient to use. Comparisons were made between the initial emittable VOC concentrations determined by the original extraction method and the proposed method. Results show good agreements between these two methods. To further validate the proposed method, the type of static chamber developed by Wang et al. (2006) was used to conduct the experiment for a type of medium density board, and formaldehyde was selected as the target compound. Based on the initial emittable concentration and partition coefficient obtained using the proposed method, and the diffusion coefficient obtained by the mercury intruding porosimetry, the chamber formaldehyde concentration was predicted and compared with the experimental measurements. Results show that the predicted chamber VOC concentration using the measured parameters agree well with the experimental data.

Correlation between the solid/air partition coefficient and liquid molar volume for VOCs in building materials

A correlation between partition coefficients, K, of dry building material and liquid molar volume of volatile organic compounds (VOCs) in it, v l, is presented. Experiment for determining the partition coefficients of the target VOCs including benzene, toluene, ethylbenzene for two kinds of building materials was conducted by a method developed by us. The experimental data verified the correlation. Also the correlation was supported well by the experimental data in the literature. It is found that the correlation can predict the partition coefficients of VOCs with similar structure in the same building material.

Impacts of environmental conditions on the sorption of volatile organic compounds onto tire powder

A series of batch tests were performed and the impacts of environmental conditions and phase change on the sorption of volatile organic compounds (VOCs) were investigated. Benzene, trichloroethylene, tetrachloroethylene, and ethylbenzene were selected as target VOCs. Sorption of VOCs onto tire powder was well demonstrated by a linear-partitioning model. Water–tire partition coefficients of VOCs (not tested in this study) could be estimated using a logarithmic relationship between observed water–tire partition coefficients and octanol–water partition coefficients of the VOCs tested. The target VOCs did not seem to compete with other VOCs significantly when sorbed onto the tire powder for the range of concentrations tested. The influence of environmental conditions, such as pH and ionic strength also did not seem to be significant. Water–tire partition coefficients of benzene, trichloroethylene, tetrachloroethylene, and ethylbenzene decreased as the sorbent dosage increased. However, they showed stable values when the sorbent dosage was greater than 10 g/L. Air–tire partition coefficient could be extrapolated from Henry's law constants and water–tire partition coefficient of VOCs.

Determining diffusion and partition coefficients of VOCs in cement using one FLEC

The diffusion and partition coefficients of eight volatile organic compounds (VOCs) in cement slabs were experimentally determined using a field and laboratory emission cell (FLEC) system based on the method developed in a previous study on the water vapor diffusion. A cement slab planted with a mixture of eight VOCs was placed in an one-FLEC system to undergo the mass diffusion in the slab and the emission to air flowing through the FLEC. The concentration of each VOC in the air flowing out of the FLEC was measured according to the EPA Method TO-17 using sorbent tube-automatic thermal desorption (ATD) and the gas chromatography-mass spectrum detector (GC-MSD) system. The diffusion and partition coefficients were then obtained by solving the inverse problem of the one-dimensional unsteady mass diffusion equations in the cement slab. And, the partition coefficient was also obtained from the total mass transfer estimated from the VOC concentration measurements and air flowrate, which was equivalent to the headspace concentration-weighting method.

Empirical Relations Predicting Human and Rat Tissue:Air Partition Coefficients of Volatile Organic Compounds

Based on the hypothesis that tissue partitioning of volatile organic compounds (VOCs) is due to lipophilic and hydrophilic interactions with tissue components, empirical relations are established between olive oil (Poil:air), saline (Psaline:air), and tissue partition coefficients (Ptissue:air) for human and rat tissues. Reported values of partition coefficients of a wide range of VOCs with distinct chemical structures (n = 137) have been compiled from the literature. Bilinear regression analysis shows that partition coefficients of VOCs in human blood, brain, fat, liver, kidney, and muscle tissues are well described by a linear combination of Poil:air and Psaline:air with tissue-specific regression coefficients. The regression coefficient associated with the hydrophilic component of VOC partitioning in rat tissues is systematically higher than that of human tissues. For the human model, tissue concentrations calculated from predicted partition coefficients are generally within a factor 4 of tissue concentrations calculated from experimentally observed partition coefficients. These results demonstrate that, without prior knowledge of tissue composition, it is possible to obtain estimates of human tissue partition coefficients of VOCs with an accuracy that is in the same range as that commonly used in risk assessment.