Determination of distribution coefficients of polycyclic aromatic nitrogen heterocycles using solid-phase microextraction

The possibility and the efficiency of solid-phase microextraction (SPME) for determination of distribution coefficients of polycyclic aromatic nitrogen heterocycles (PANHs) in aqueous samples are presented in this study. Influence of sample extraction conditions, extraction time, stirring rate, pH, salinity and temperature were tested to optimize extraction efficiency. Three types of fibre sorbent layers, PDMS, PDMS/DVB and PA, were tested and fibre/water distribution coefficients, K_{f s} , were calculated. The extraction efficiency for PANHs increased in the order PDMS?<?PA?<?PDMS/DVB. Values of log?K_fs ranged from 0.2 to 2.7 for PDMS, from 0.4 to 3.6 for PA and from 1.4 to 4.4 for PDMS/DVB. The values of log?K_fs were correlated with octanol/water distribution coefficients log?K_ow . The relationship between log?K_fs and log?K_ow shows linear response with regression coefficient in the range of 0.985 and 0.997.     

Determination of oil–water partition coefficients of polar compounds: silicone membrane equilibrator vs. SPME passive sampler

Experimental determination of oil-water partition coefficients often poses difficulties associated with emulsion formation. The aim of this work was to find an appropriate technique for determination of oil–water partition coefficients of polar, nonvolatile compounds. Two different methods were tested. The first method used a “silicone membrane equilibrator.” For the second method, solid-phase microextraction (SPME) fibers with a polyacrylate (PA) coating were used as a passive sampler. With both methods, oil–water partition coefficients for 14 compounds with polar functional groups were determined at 37 °C with good repeatability (standard deviation 0.11 log units or lower). The partition coefficients determined with the silicone membrane equilibrator method ranged from 0.50 to 3.49 log units. The oil–water partition coefficients obtained with the PA-SPME passive sampling approach were significantly higher than those obtained with the silicone membrane equilibrator method for nine of 14 compounds. The differences were up to 0.39 log units (i.e., a factor of 2.5). Additional experiments suggested that this difference occurred because the sorption properties of the PA fibers used were influenced by the surrounding phase, e.g., through swelling of the polymer phase. Therefore, the SPME passive sampling method using PA fibers seems to be less reliable, whereas the silicone membrane equilibrator method was found to be a convenient technique for the determination of oil–water partitioning.     

Improvement in gas separation properties of a polymeric membrane through the incorporation of inorganic nano‐particles

The present work tries to introduce a high‐performance nano‐composite membrane by using polydimethylsiloxane (PDMS) as its main polymer matrix to meet some specific requirements in industrial gas separations. Different nano‐composite membranes were synthesized by incorporating various amounts of nano‐sized silica particles into the PDMS matrix. A uniform dispersion of nano‐particles in the host membranes was obtained. The nano‐composite membranes were characterized morphologically by scanning electron microscopy and atomic force microscopy. Separation properties, permeability, and ideal selectivity of C₃H₈, CH₄, and H₂ through the synthesized nano‐composite membranes with different nano‐particle contents (0.5, 1, 1.5, 2, 2.5, and 3 wt%) were investigated at different pressures (2, 3, 4, 5, 6, and 7 atm) and constant temperature (35°C). It was found out that a 2 wt% loading of nano‐particles into the PDMS matrix is optimal to obtain the best separation performance. Afterwards, sorption experiments for the synthesized nano‐composite membranes were carried out, and diffusion coefficients of the gases were calculated based on solution‐diffusion mechanism. Gas permeation and sorption experiments showed an increase in sorption and a decrease in diffusion coefficients of the gases through the nano‐composite membranes by adding nano‐particles into the host polymer matrix. Copyright © 2011 John Wiley & Sons, Ltd.     

Air/polymer distribution coefficients for polycyclic aromatic hydrocarbons by solid-phase microextraction sampling

Two methods to estimate distribution coefficients (K) between air and poly(dimethylsiloxane) (PDMS) coating of solid-phase microextraction (SPME) fibers for eight low molecular polycyclic aromatic hydrocarbons (PAHs) there are presented. The PDMS phases were used for determination of the coefficients according to equilibrium theory with help of a developed static calibration system (SCS). Another way to estimate the coefficients is based on the use of a linear relationship between the logarithm of the coefficients (log K) and linear temperature-programmed retention indexes (LTPRI) of the compounds without necessity to calibrate. The log K values for both of methods ranged from 5.2 (naphthalene) to 8.9 (pyrene) at 22 degrees C. Relative standard deviation (R.S.D.) of log K for each compound determined by static calibration was no more than 5.3%. R.S.D. of retention times for LTPRI indices did not exceed 0.28% for repeated injection. All experiments were implemented on a GC-MS system.     

Characterization of room-temperature ionic liquids by the Abraham model with cation-specific and anion-specific equation coefficients

Gas-to-RTIL (room-temperature ionic liquid) partition coefficients have been compiled for 592 different solute-RTIL combinations. These partition coefficients were converted into water-to-RTIL partition coefficients using the corresponding gas-to-water partition coefficients. Both sets of partition coefficients were analyzed using the Abraham solvation parameter model with cation-specific and anion-specific equation coefficients. The derived equations correlated the experimental gas-to-RTIL and water-to-RTIL partition coefficient data to within 0.10 and 0.14 log units, respectively. The 8 sets of calculated cation-specific equation coefficients and 4 sets of calculated anion-specific equation coefficients can be combined to yield expressions capable of predicting the partition coefficients of solutes in 32 different RTILs.     

Sorption thermosiphon apparatus (STA): A novel and accurate system for gas mixtures sorption measurements

One of the main challenges in membrane gas separation is the plasticizing effect that reduces selectivity. For a better understanding of this phenomenon, the knowledge of the sorption behavior of each component of the mixture is necessary. For this purpose, the sorption thermosyphon apparatus (STA), was successfully designed and tested with gas sorption measurements. One of the main advantages of the STA compared to actual other methods is to ensure concentration uniformity at the headspace using a thermosiphon, as pressure decay is recorded. The equilibrium condition is not disturbed during the sampling and allow the obtention of accurate data at the end of the sorption experiment. To validate the novel system, the sorption, diffusion and permeation coefficients of pure CO2 and CH₄, as well as for a CO₂/CH₄ (50/50) mixture, in polydimethylsiloxane (PDMS) were obtained through STA and other experimental techniques showing good agreement with literature data.     

Prediction of cyclohexane-water distribution coefficients for the SAMPL5 data set using molecular dynamics simulations with the OPLS-AA force field

All-atom molecular dynamics simulations were used to predict water-cyclohexane distribution coefficients \(D_{cw}\) of a range of small molecules as part of the SAMPL5 blind prediction challenge. Molecules were parameterized with the transferable all-atom OPLS-AA force field, which required the derivation of new parameters for sulfamides and heterocycles and validation of cyclohexane parameters as a solvent. The distribution coefficient was calculated from the solvation free energies of the compound in water and cyclohexane. Absolute solvation free energies were computed by an established protocol using windowed alchemical free energy perturbation with thermodynamic integration. This protocol resulted in an overall root mean square error in \(\log D_{cw}\) of almost 4 log units and an overall signed error of ?3 compared to experimental data. There was no substantial overall difference in accuracy between simulating in NVT and NPT ensembles. The signed error suggests a systematic error but the experimental \(D_{cw}\) data on their own are insufficient to uncover the source of this error. Preliminary work suggests that the major source of error lies in the hydration free energy calculations.     

Estimating the PDMS-Coated, SPME-Fibre/Water- and Fibre/Gas-Partition Coefficients of Chlorinated Ethenes by Headspace-SPME

In this work, a simple, fast and reproducible method is presented for the determination of fibre/liquid-phase and fibre/gas-phase partition coefficients of five chlorinated ethenes on a poly-(dimethylsiloxane), PDMS-coated, solid-phase microextraction fibre, by employing a headspace HS-SPME coupled with gas chromatography. The partition coefficients were estimated by a numerical method using a Level-I fugacity method coupled with parameter-estimation software. Dimensionless partition coefficients between SPME fibre and liquid as well as gas phases were obtained at temperatures of 10 °C, 25 °C and 30 °C. The partition coefficients of the fibre and the gas phase, K _fg, increase with decreasing temperature by a factor of ≈2 to 6, and they are directly proportional to the linear slope of the regression line. The same tendency is observed for the partition coefficient of the fibre and liquid phase, K _fw, in a factor ≈1.2 to 2.0. The sorption enthalpy is higher in the gas phase; therefore, the sorption onto the fibre is favoured at lower temperatures. The correlation of the log K _ow versus log K _fw and log K _oa versus log K _fg shows a linear relationship with the number of chlorine atoms in the C = C molecule. Long-term experiments resulted in sorption to Teflon surfaces and possible losses in 43 mL vials, not observed in 250 mL Boston bottles.     

Abraham model correlations describing the solubilising ability of peanut oil

Experimental data have been compiled from the published literature for the logarithm of the gas-to-peanut oil partition coefficient, log K, and for the logarithm of the water-to-peanut oil partition coefficient, log P, for a series of 93 solutes having a wide range of solute polarities and hydrogen-bonding character. The two sets of partition coefficients were correlated with the Abraham solvation parameter model. The derived Abraham model correlations described the experimental log K and log P values within standard deviations of 0.13 and 0.14 log units, respectively. Principal component analysis was used to compare the solvent properties of peanut oil to four other natural oils (olive oil, soybean oil, triolein and oleyl alcohol). Peanut oil was found to be close to olive oil and soybean oil, and quite far away from triolein and oleyl alcohol.     

Gas sorption,diffusion, and permeation in poly(dimethylsiloxane)

The permeability of poly(dimethylsiloxane) [PDMS] to H₂, O₂, N₂, CO₂, CH₄, C₂H₆, C₃H₈, CF₄, C₂F₆, and C₃F₈, and solubility of these penetrants were determined as a function of pressure at 35 °C. Permeability coefficients of perfluorinated penetrants (CF₄, C₂F₆, and C₃F₈) are approximately an order of magnitude lower than those of their hydrocarbon analogs (CH₄, C₂H₆, and C₃H₈), and the perfluorocarbon permeabilities are significantly lower than even permanent gas permeability coefficients. This result is ascribed to very low perfluorocarbon solubilities in hydrocarbon‐based PDMS coupled with low diffusion coefficients relative to those of their hydrocarbon analogs. The perfluorocarbons are sparingly soluble in PDMS and exhibit linear sorption isotherms. The Flory–Huggins interaction parameters for perfluorocarbon penetrants are substantially greater than those of their hydrocarbon analogs, indicating less favorable energetics of mixing perfluorocarbons with PDMS. Based on the sorption results and conventional lattice solution theory with a coordination number of 10, the formation of a single C₃F₈/PDMS segment pair requires 460 J/mol more energy than the formation of a C₃H₈/PDMS pair. A breakdown in the geometric mean approximation of the interaction energy between fluorocarbons and hydrocarbons was observed. These results are consistent with the solubility behavior of hydrocarbon–fluorocarbon liquid mixtures and hydrocarbon and fluorocarbon gas solubility in hydrocarbon liquids. From the permeability and sorption data, diffusion coefficients were determined as a function of penetrant concentration. Perfluorocarbon diffusion coefficients are lower than those of their hydrocarbon analogs, consistent with the larger size of the fluorocarbons. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 415–434, 2000     

Development of Abraham model IL-specific correlations for N-triethyl(octyl)ammonium bis(fluorosulfonyl)imide and 1-butyl-3-methylpyrrolidinium bis(fluorosulfonyl)imide

ABSTRACT

Abraham model correlations are derived for describing gas-to-ionic liquid and water-to-ionic liquid partition coefficients from published experimental data for solutes dissolved in both N-triethyl(octyl)ammonium bis(fluorosulfonyl)imide and 1-butyl-3-methyl-pyrrolidinium bis(fluorosulfonyl)imide. Derived Abraham model correlations describe the observed partition coefficient data to within 0.13 log units. As part of the current study the existing equation coefficients for the N-triethyl(octyl)ammonium cation were updated and reported for the first time were equation coefficients for the bis(trifluorosulfonyl)imide anion.     

Sorption and diffusion of VOCs in DAY zeolite and silicalite-filled PDMS membranes

The sorption and diffusion properties of ethanol, 1,1,1-trichloroethane (TCA) and trichloroethylene (TCE) were determined in silicalite-filled and dealuminized-Y-zeolite (DAY)-filled poly[dimethylsiloxane] (PDMS) membranes at 25, 100 and 150°C. Zeolite filling results in increased solubility coefficients (S) for polar solvents like ethanol over pure PDMS. No significant increase in S is observed in case of TCA and TCE which act as good solvents for PDMS. However, at higher temperatures, the sorption is higher in zeolite-filled membranes even for the good solvents. The VOC diffusivity decreases with increasing degree of zeolite filling because of higher characteristic diffusion time in zeolites (for ethanol) and increasing tortuosity of the diffusion path (for TCA). Due to the presence of carbon=carbon double bond, TCE exhibits marginal diffusivity drop in zeolite-filled membranes. The specific zeolite-polymer interactions, that is, tendency of zeolite pore blocking by polymer chains or the formation of voids on zeolite-polymer interface are influenced by the zeolite pore size and type of VOC permeating through the composite membrane. The variation in experimentally observed ethanol permeability due to zeolite filling could be qualitatively estimated from the sorption-diffusion data.     

The solution and transport of gases in poly(N-butyl methacrylate) in the glass transition region. I. Absorption-desorption measurements

Solubility coefficients, S, and diffusion coefficients, D, have been determined for ethane and n-butane in poly(n-butyl methacrylate) (PnBMA) by the microbalance technique in the temperature range from ?14 to 50°C, which encompasses the glass transition of the polymer (22–35°C). S and D for ethane were found to be independent of penetrant pressure and concentration at all temperatures studied No transition to “dual-mode” sorption behavior, as reported for a number of penetrants in glassy polymers, was observed with ethane, even at the lowest experimental temperature. Plots of log S and log D versus 1-T, the reciprocal absolute temperature, were linear for the ethane-PnBMA system and did not exhibit discontinuities in the glass transition region. The above results suggest that the same mechanism of solution and transport of ethane in PnBMA is operative both above and below the glass transition of the polymer under the experimental conditions. This behavior is attributed to the low “excess” free volume of glassy PnBMA, as indicated by the small difference between the coefficients of thermal expansion of this polymer in its rubbery and glassy states. Possible conditions for the appearance of dual-mode gas sorption are discussed. A similar study with the n-butane-PnBMA system showed that the polymer was plasticized by the penetrant below 20°C, due to the higher solubility of n-butane compared with that of ethane in PnBMA.     

INS and IR study of intermolecular interactions at the fumed silica-polydimethylsiloxane interphase, Part I. Polydimethylsiloxane models

A vibration spectra study of the interphase of fumed silica andpolydimethylsiloxane (PDMS) particles highlights the microscopic interactionmechamisms in the system. This study in general involves an extendedexamination of free silica and PDMS components as well as their absorptioncomplexes. Part 1, the present paper, deals with vibration analysis of freePDMS oligomer molecules. The results provide a basis for assignment ofvibration frequencies not only for PDMS polymers but also for silica andsilica-PDMS adsorption complexes and give the reference spectra of species atthe fumed silica-PDMS interphase. Vibrations have been investigated involvingboth experimental and computational approaches. Experiments were performed inthe framework of infrared (FTIR) and inelastic neutron scattering (INS andAWDS) techniques. Spectra interpretation was carried out on the basis ofquantum chemical (QCh) semiempirical calculations using AM1 and PM3parameterisation and application of an original software for spectra analysisCOSPECO involving direct and inverse spectral problem solution and spectraassignment.     

Sorption and partitioning parameters of benzotriazole compounds

Benzotriazole compounds have major commercial applications as anticorrosive agents in automotive antifreeze and airplane deicer fluids. This study assesses the sorption of benzotriazole (BT), 5-methylbenzotriazole (MBT), and 5-chlorobenzotriazole (CBT) from aqueous solutions to four top soils. The concentration range of 10-500 mg l⁻¹ was used with soils differing in total organic carbon content from 0.27 to 1.72%. Batch systems facilitated the equilibrium sorption with analysis by HPLC. The sorption of these compounds was as much as 60% by mass to a soil with 0.33% Org. C. The log octanol-water partition coefficients (log K_ow) were determined to be 1.23 for BT, 1.89 for MBT, and 2.17 for CBT. The relationship between the log of the sorption partition coefficient, log K_oc and log K_ow differed from previous correlations because hydrophobicity was not the only factor affecting sorption. These compounds have substantial permanent dipole moments as well as being hydrophobic. At high pH where CBT molecules approach their pK_a, sorption was approximately 50% less (by mass) than that of relatively non-ionized CBT molecules.     

Infinite dilution activity coefficients and gas-to-liquid partition coefficients of organic solutes dissolved in 1-sec-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and in 1-tert-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Inverse gas chromatography was used to measure infinite dilution activity coefficients and gas-to-liquid partition coefficients for 48 organic solute probes in either 1-sec-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-tert-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide in the temperature range from 323.15 to 373.15 K. Partial molar excess enthalpies of solution were calculated from the variation of the infinite dilution activity coefficients with temperature. Abraham model correlations were also derived from the experimental partition coefficient data. The derived Abraham model correlations describe the observed partition coefficients to within 0.11 log units.     

Chromatographic models for the sorption of neutral organic compounds by soil from water and air.

The solvation parameter model is used to construct models for the estimation of the soil-water and soil-air distribution constants and to characterize the contribution of fundamental intermolecular interactions to the underlying sorption processes. Wet soil is shown to be quite cohesive and polar but relatively non-selective for dipole-type, lone-pair electron and hydrogen-bond interactions. Using a comparison of system constant ratios chromatographic systems employing reversed-phase liquid chromatography on polar bonded phases are shown to provide suitable models for estimating soil-water distribution constants. No suitable gas chromatographic models were found for the soil-air distribution constant but the requirements for such a system are indicated. Models are also provided for adsorption at the air-water interface. Estimation methods based on either the solvation parameter model or chromatographic model reproduce experimental distribution constants for a wide variety of compounds with a similar error (0.2-0.3 log units) to that expected in the experimental data.     

On the influence of the resonance and inductive effects on the hydrophobicity of the isomeric methylquinolones analyzed by means of RP-HPLC

Summary Hydrophobicity of methylquinolines was compared with their retention data measured on two stationary phases by reversed-phase HPLC, and with the experimental partition coefficients (log P). The influence of the substituent position on the hydrophobicity is discussed and a two-parameter correlation equation is proposed permitting the prediction of the log k values with help of the inductive and resonance effects.