Oil-water Partitioning Research Articles

Incorporating Oil / Water Partitioning in Risk Calculations for PAHs in Petroleum Impacted Soils and Sediments

ABSTRACT Polycyclic aromatic hydrocarbons (PAHs) may drive remediation at impacted soil or sediment sites. Current equations for calculating the PAH concentrations in soil that are protective of underlying groundwater (i.e., soil screening levels, or SSLs) generally assume a three-phase partitioning model, wherein PAHs partition among the soil matrix, porewater, and pore air. This simplified model does not consider the oil phase, and therefore overestimates the dissolved PAH concentration, and consequently, overpredicts the mobility and toxicity of PAHs to receptors especially when the source of PAHs is oil. This results in unnecessarily stringent cleanup goals and adds to the cost of treatment and management of impacted soils. Complicating factors leading to the overestimation of dissolved PAH are that oil weathering (1) decreases to the effective solubility of the lower molecular weight PAHs, and (2) the presence of the oil itself increases PAH retention in the oil phase, thereby reducing aqueous/dissolved PAH concentrations. This is particularly important when oil is both the source and the factor controlling its solubility. In this paper, we have incorporated additional partitioning factors into existing SSL equations to capture the impact of oil weathering on PAH partitioning: The oil-water partitioning coefficient (KOIL ) for crude oils was measured at different stages of weathering using a passive sampling device (PSD). Results confirm that current methods for deriving SSLs are highly conservative and that the aqueous concentrations and mobility of PAHs are lower in soils and sediments that contain weathered oils. Thus, the mobility of PAHs in historically impacted soils is much lower than what is assumed when calculating SSLs for soil-leaching-to-groundwater scenarios.

In Vitro Gastrointestinal Stability of Lipophilic Polyphenols is Dependent on their Oil-Water Partitioning in Emulsions: Studies on Curcumin, Resveratrol, and Quercetin.

Many lipophilic polyphenols have low bioavailability because of their poor solubility and chemical stability within the human gut. The encapsulation of these polyphenols within digestible lipid droplets can improve their solubility and stability. However, there is currently a poor understanding of how the molecular and physicochemical properties of specific polyphenols impact these characteristics. In this study, the factors influencing the solubility and stability of different polyphenols (curcumin, resveratrol, and quercetin) under simulated gastrointestinal conditions were examined when they were delivered in the form of soybean oil-in-water nanoemulsions containing quillaja saponin-coated droplets (d32 ≈ 0.15 μm; ζ = -63 mV; pH 5). The polyphenols were loaded into the lipid droplets using a pH-driven method, which is based on the pH-dependent electrical charge, oil-water partitioning, and water-solubility of these molecules. The encapsulation efficiency of all three polyphenols was relatively high (75-87%). However, their chemical stability under gastrointestinal conditions (i.e., the % remaining after exposure to gastrointestinal conditions) differed considerably: quercetin (44%), curcumin (92%), and resveratrol (100%). This effect was mainly attributed to the lower logD value of quercetin (2.17) than those of resveratrol (3.39) and curcumin (4.12). As a result, a high fraction (>50%) of quercetin was located within the aqueous gastrointestinal fluids, where it would be more prone to chemical degradation or precipitation. The fraction of the polyphenols solubilized in the gastrointestinal fluids (bioaccessibility) followed a different trend: curcumin (57%) < quercetin (73%) < resveratrol (76%). This effect was attributed to the chemical instability and/or binding of curcumin with other molecules in the simulated intestinal conditions. These results provide useful information for designing nanoemulsion-based delivery systems to improve the efficacy of lipophilic polyphenols.

A Single Well Chemical Tracer model that accounts for temperature gradients, pH changes and buffering

We present the first ever Single Well Chemical Tracer (SWCT) model that incorporates temperature gradients and pH-driven ethyl acetate hydrolysis rate changes when buffering by either calcite in the oil-bearing formation or by chemical species in the injected brine are accounted for. The model is applied to four generic cases with SWCT test, rock formation and brine composition data based on published values. An analytical model is used to calculate how the brine injection temperature decreases with time and an axially symmetric numerical model is used to simulate the cooling of the oil-bearing formation, chemical reactions and transport of species in the reservoir. The primary oil-water partitioning tracer ethyl acetate hydrolyses into the secondary water tracer ethanol and acetic acid that lowers the pH and changes the hydrolysis rate. The acid driven pH decrease may be significantly reduced by pH buffering mechanisms. We investigate four different buffer models. Model 1 may represent a sandstone with calcite cement. In Model 2, also with calcite cement, the brine has less calcium but more bicarbonate and initially lower pH than Model 1. Model 3 is a clean sandstone without calcite cement and the brine contains no calcium but much bicarbonate. Model 4 has no buffer capacity neither in the brine nor in the target formation. Although we discuss only four models, they are quite different and represent an important subset of the realistic SWCT test parameter space. A temperature gradient develops across the primary tracer bank in all four models and this causes the secondary tracer to be displaced away from the wellbore relative to the primary tracer. We find that most of the ethyl acetate hydrolysis takes place during shut-in. The residual oil saturation (Sor) is estimated from the synthetic tracer production curves using the simple chromatographic separation equation as well as with the mean residence time correction. The two methods underestimate the true Sor value (22%) by 3–5 and 3–11% (saturation points), respectively. These results demonstrate that the ‘handicap’ created by the temperature gradient together with the pH-driven hydrolysis rate changes should be taken into account in Sor estimates. We suggest that SWCT tests may be used to evaluate the effective wettability of the target formation at a modest extra cost. Using water tracers with very low quantification limits as primary tracers should reduce or even eliminate the problems caused by temperature gradients and pH-driven hydrolysis rate changes since they will travel well ahead of the temperature gradient and the small amount of acid generated will produce only an insignificant reduction in pH.

Partitioning Behavior and Interfacial Activity of Phenolic Acid Derivatives and their Impact on \u03b2-Lactoglobulin at the Oil-Water Interface

Proteins are able to stabilize dispersed food systems due to their amphiphilic nature, acting as emulsifiers. Their interfacial properties can be influenced by different methods, including the formation of protein-phenol nanocomplexes. In this study, the interfacial behavior of phenolic compounds and protein-phenol nanocomplexes was first characterized according to the oil-water partitioning behavior of phenolic acid derivatives according to their molecular structure and its impact on interfacial tension. The influence of the phenolic compounds on protein film formation and its properties by dilatational rheology was then evaluated. The most phenolic acid derivatives are predominantly present in the aqueous phase. Despite their hydrophobic benzene body, weak interfacial activity was observed depending on their chemical structure. This result supports possible protein-phenol nanocomplex formation in the aqueous phase and possible interactions at the oil-water interface. Protein-phenol nanocomplexes showed decreased interfacial adsorption properties and decreased viscoelastic interfacial behavior, depending on the expansion of the delocalized π-electrons in the phenol.

Affinity of small-molecule solutes to hydrophobic, hydrophilic, and chemically patterned interfaces in aqueous solution

Performance of membranes for water purification is highly influenced by the interactions of solvated species with membrane surfaces, including surface adsorption of solutes upon fouling. Current efforts toward fouling-resistant membranes often pursue surface hydrophilization, frequently motivated by macroscopic measures of hydrophilicity, because hydrophobicity is thought to increase solute-surface affinity. While this heuristic has driven diverse membrane functionalization strategies, here we build on advances in the theory of hydrophobicity to critically examine the relevance of macroscopic characterizations of solute-surface affinity. Specifically, we use molecular simulations to quantify the affinities to model hydroxyl- and methyl-functionalized surfaces of small, chemically diverse, charge-neutral solutes represented in produced water. We show that surface affinities correlate poorly with two conventional measures of solute hydrophobicity, gas-phase water solubility and oil-water partitioning. Moreover, we find that all solutes show attraction to the hydrophobic surface and most to the hydrophilic one, in contrast to macroscopically based hydrophobicity heuristics. We explain these results by decomposing affinities into direct solute interaction energies (which dominate on hydroxyl surfaces) and water restructuring penalties (which dominate on methyl surfaces). Finally, we use an inverse design algorithm to show how heterogeneous surfaces, with multiple functional groups, can be patterned to manipulate solute affinity and selectivity. These findings, importantly based on a range of solute and surface chemistries, illustrate that conventional macroscopic hydrophobicity metrics can fail to predict solute-surface affinity, and that molecular-scale surface chemical patterning significantly influences affinity-suggesting design opportunities for water purification membranes and other engineered interfaces involving aqueous solute-surface interactions.

Equilibrium Partitioning of Naphthenic Acid Mixture Part 2: Crude Oil-Extracted Naphthenic Acids

Crude oil naphthenic acids can partition into the water phase during oil production. Variations in production parameters such as temperature, pressure, pH, and water cut affect partitioning. In a previous article, a method was developed to determine the partition ratio for mixtures of naphthenic acids and tested on a commercial acid mixture. In this study, the method is implemented on a naphthenic acid mixture extracted from an acidic crude oil. Compositional analysis of the extracted acid mixture reveals a broad structural distribution consisting mainly of saturated ring structures with 2 to 3 rings. Examination of the GC/MS method revealed a distribution bias toward low molecular weight compounds, and a correction method was explained and applied. The equilibrium partitioning as a function of pH for the acid mixture and molecular mass ranges within the acid mixture was determined by GC/MS. An extracted crude oil acid mixture dissolved in toluene was used as oil phase, and 3.5 wt % NaCl aqueous buffers were used as water phase. Dividing the acid mixture into molecular weight ranges, characterized by a single partition ratio Pwo allowed the oil–water partitioning to be successfully modeled. The variation of the cologarithm of the partition ratio pPwo with naphthenic acid molecular weight was compared with previously published experimental and simulated data. The presence of calcium reduced the partitioning of the acid mixture at high pH for larger acid molecules. Analysis of the resulting oil phase revealed a calcium content consistent with oil-soluble calcium naphthenate in agreement with results found for a commercial acid mixture.

Experimental simulation of crude oil-water partitioning behavior of BTEX compounds during a deep submarine oil spill

The conventional shake flask technique for determining oil-water partition ratios of benzene, toluene, ethylbenzene and xylene (BTEX) cannot accurately assess the extremes of high pressure and low water temperatures found in submarine oil spill conditions. An oil-water partitioning device has been constructed to experimentally simulate the partition behavior of BTEX compounds under submarine oil spill conditions, using simulated live oil (methane-charged), with saline waters over a range of pressure (2–15MPa) and temperature (4–20°C). Within the investigated ranges, the partition ratios of BTEX compounds increase proportionally with an increase in methane charging pressure (oil saturation pressure) and the degree of BTEX alkylation, and decrease with increase in temperature. The variation of the partition ratio values due to changes in system pressure and increasing oil methane concentration, is much more significant than those seen due to change in the temperature over the range studied. This data may be used in near-field and far-field distribution modeling of the environmental fate of highly toxic BTEX compounds, derived from submarine oil spills and their impact on the ecosystem. The parameters will also aid in the prediction of oil migration and dispersion away from the spill thus helping to improve response strategies.

222 Rn as Natural Tracer for LNAPL Recovery in a Crude Oil-Contaminated Aquifer

The objective of this study was to investigate whether 222Rn in groundwater can be used as a tracer for light non-aqueous phase liquid (LNAPL) quantification at a field site treated by dual-phase LNAPL removal. After the break of a pipeline, 5 ha of soil in the nature reserve Coussouls de Crau in southern France was contaminated by 5100 m3 of crude oil. Part of this oil seeped into the underlying gravel aquifer and formed a floating oil body of about 3.9 ha. The remediation consists of plume management by hydraulic groundwater barriers and LNAPL extraction in the source zone. 222Rn measurements were performed in 21 wells in and outside the source zone during 15 months. In uncontaminated groundwater, the radon activity was relatively constant and remained always >11 Bq/L. The variability of radon activity measurements in wells affected by the pump-and-skim system was consistent with the measurements in wells that were not impacted by the system. The mean activities in wells in the source zone were, in general, significantly lower than in wells upgradient of the source zone, owing to partitioning of 222Rn into the oil phase. The lowest activities were found in zones with high non-aqueous phase liquid (NAPL) recovery. LNAPL saturations around each recovery well were furthermore calculated during a period of high groundwater level, using a laboratory-determined crude oil–water partitioning coefficient of 38.5 ± 2.9. This yielded an estimated volume of residual crude oil of 309 ± 93 m3 below the capillary fringe. We find that 222Rn is a useful and cheap groundwater tracer for finding zones of good LNAPL recovery in an aquifer treated by dual-phase LNAPL removal, but that quantification of NAPL saturation using Rn is highly uncertain.

Multiscale Modeling of Mass Transfer and Adsorption in Liquid–Liquid Dispersions. 2. Application to Calcium Naphthenate Precipitation in Oils Containing Mono- and Tetracarboxylic Acids

A dynamic multicomponent mass transport model is constructed and solved to determine the interfacial composition and bulk phase concentrations of surfactant mixtures containing a synthetic tetracarboxylic acid (BP10) and decanoic acid (DA) for water droplets dispersed in oil. The transport model employs a molecular mixed monolayer adsorption model that was parametrized by MD simulation and interfacial tension experiments in part 1 [Kovalchuk, K.Riccardi, E.Grimes, B. A. Ind. Eng. Chem. Res. 2014, 10.1021/ie501295k]. The model accounts for oil–water partitioning, the pH determined dissociation state of the acids, and micelle formation in the water phase. Since the interfacial concentration of tetracarboxylic acids in crude oil emulsions is hypothesized to influence the extent of fouling by calcium naphthenate precipitation, trends for the amount of calcium naphthenate precipitate formed in the system can be predicted as a function of the water volume fraction for various BP10:DA concentration ratios and dr...

Chronic toxicity of heavy fuel oils to fish embryos using multiple exposure scenarios

The chronic toxicity to rainbow trout (Oncorhynchus mykiss) embryos of heavy fuel oil (HFO) 6303, weathered HFO 6303, HFO 7102, and medium South American (MESA) crude oil was assessed by different exposure regimes. These included water accommodated fractions (WAF; water in contact with floating oil), chemically enhanced WAF (CEWAF; oil dispersed with Corexit 9500), and effluent from columns of gravel coated with stranded oil. Heavy fuel oil WAF was nontoxic and did not contain detectable concentrations of hydrocarbons, likely because the high density and viscosity of HFO prevented droplet formation. In contrast, chemically dispersed HFO and effluent from columns of stranded HFO contained measurable concentrations of alkyl polycyclic aromatic hydrocarbons (PAH), coincident with embryo toxicity. These exposure regimes enhanced the surface area of oil in contact with water, facilitating oil-water partitioning of hydrocarbons. Heavy fuel oil was consistently more toxic to fish than crude oil and the rank order of alkyl PAH concentrations in whole oil were sufficient to explain the rank order of toxicity, regardless of exposure method. Thus, the propensity of HFO to sink and strand in spawning shoals creates a long-term risk to developing fish because of the sustained release of PAHs from HFO to interstitial waters. Further, PAH monitoring is key to accurate risk assessment.

Breaking of the Bancroft rule for multiple emulsions stabilized by a single stimulable polymer.

We investigated emulsions of water and toluene stabilized by (co)polymers consisting of styrene (S) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) monomer units with different compositions and structures such as a PDMAEMA homopolymer, a P(S-co-DMAEMA) random copolymer and various PS-b-PDMAEMA and PS-b-(S-co-DMAEMA) block copolymers. The model system is used to study the fundamental conditions under which the different kinds of polymer-stabilized emulsions (direct oil in water, inverse water in oil and multiple emulsions) are stabilized or destabilized by pH change (at constant temperature). Polymer properties like chain conformation at the toluene-water interface as probed by SANS and neutron reflectivity at the liquid-liquid interface, the oil-water partitioning of the polymer chains (Bancroft's rule of thumb) as determined by UV spectroscopy and interfacial tensions measured by the rising and spinning drop techniques are determined. Overall, results evidence that the curvature sign, as defined by positive and negative values as the chain segments occupy preferentially the water and toluene sides of the interface respectively, reliably predicts the emulsion kind. In contrast, the Bancroft rule failed at foreseeing the emulsion type. In the region of near zero curvature the crossover from direct to inverse emulsions occurs through the formation of either unstable coexisting direct and inverse emulsions (i) or multiple emulsions (ii). The high compact adsorption of the chains at the interface as shown by low interfacial tension values does not allow to discriminate between both cases. However, the toluene-water partitioning of the polymeric emulsifier is still a key factor driving the formation of (i) or (ii) emulsions. Interestingly, the stabilization of the multiple emulsions can be tuned to a large extent as the toluene-water polymer partitioning can be adjusted using quite a large number of physico-chemical parameters linked to polymer architecture like diblock length ratio or polymer total molar mass, for example. Moreover, we show that monitoring the oil-water partitioning aspect of the emulsion system can also be used to lower the interfacial tension at low pH to values slightly higher than 0.01 mN m(-1), irrespective of the curvature sign.

Binding of Serotonin to Lipid Membranes

Serotonin (5-hydroxytryptamine, 5-HT) is a prevalent neurotransmitter throughout the animal kingdom. It exerts its effect through the specific binding to the serotonin receptor, but recent research has suggested that neural transmission may also be affected by its nonspecific interactions with the lipid matrix of the synaptic membrane. However, membrane-5-HT interactions remain controversial and superficially investigated. Fundamental knowledge of this interaction appears vital in discussions of putative roles of 5-HT, and we have addressed this by thermodynamic measurements and molecular dynamics (MD) simulations. 5-HT was found to interact strongly with lipid bilayers (partitioning coefficient ~1200 in mole fraction units), and this is highly unusual for a hydrophilic solute like 5-HT which has a bulk, oil-water partitioning coefficient well below unity. It follows that membrane affinity must rely on specific interactions, and the MD simulations identified the salt-bridge between the primary amine of 5-HT and the lipid phosphate group as the most important interaction. This interaction anchored cationic 5-HT in the membrane interface with the aromatic ring system pointing inward and a prevailing residence between the phosphate and the carbonyl groups of the lipid. The unprotonated form of 5-HT shows the opposite orientation, with the primary amine pointing toward the membrane core. Partitioning of 5-HT was found to decrease lipid chain order. These distinctive interactions of 5-HT and model membranes could be related to nonspecific effects of this neurotransmitter.

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.

Oil-Water Partitioning of a Synthetic Tetracarboxylic Acid as a Function of pH

The oil-water partitioning of a synthetic tetraacid acting as a model compound for indigenous C80-C82 ARN acids has been studied as a function of pH, ionic strength and type of monovalent counterion. Experimental data obtained with ultraviolet-visible and HPLC/UV analyses have been fitted to thermodynamic models based on one, two or four dissociation steps to obtain o/w partition coefficients (K wo ) of the fully protonated acid between chloroform and aqueous solutions, and its apparent acidity constant(s), pK a. As the study is conducted above the CMC of the tetraacid, in general high apparent acidity constants were obtained in the range from 6 to 8 resulting from micellization equilibria. K wo values were obtained in the range from 10−3 to 10−4, and decreasing with increasing salinity. At 50 mM K+, no conclusions could be made regarding the number of distinguishable dissociation steps, while at higher ionic strength (184 mM and 452 mM K+) and at 184 mM Na+ a model with two dissociation steps provided good fits to the experimental data. The first step was found to be given by a pK a ≈ 6.6–6.8 and the second dissociation step at pK a values ≈ 7.8–8.3. The two-step mechanism supports previous results obtained by potentiometric titrations. No significant difference in the o/w behavior was observed when changing the counterion from potassium to sodium. The main partitioning of the tetraacid in the aqueous phase occurred above pH 8, where the fully deprotonated acid was formed.

Inhibition of citral degradation in model beverage emulsions using micelles and reverse micelles

Citral is a flavour component that is widely used in the beverage, food, and fragrance industries. Citral chemically degrades over time in aqueous solutions due to acid catalysed and oxidative reactions, leading to loss of desirable flavour and the formation of off-flavours. We examined the influence of surfactant micelles (Tween 80) in the aqueous phase and reverse micelles (polyglycerol polyricinoleate, PGPR) in the oil phase on the oil–water partitioning and chemical degradation of citral in medium chain triglyceride oil-in-water emulsions. The percentage of citral in the aqueous phase of the emulsions increased with increasing Tween 80 concentration, which was attributed to its incorporation within surfactant micelles. The rate of citral degradation decreased as the Tween 80 concentration was increased from 1% to 5% w/w in both aqueous solutions and in emulsions, suggesting that citral was protected from degradation once it was incorporated into micelles. The presence of reverse micelles (5% or 10% w/w PGPR) in the oil droplets decreased the percentage of citral present within the aqueous phase of the emulsions, suggesting that citral was preferentially incorporated into the reverse micelles. In addition, the presence of reverse micelles increased the chemical stability of citral, possibly because a greater fraction remained within the oil droplets. These results show that micelle or reverse-micelle structures may be used to improve the chemical stability of citral in beverage emulsions.

Stability of Citral in Oil-in-Water Emulsions Prepared with Medium-Chain Triacylglycerols and Triacetin

Citral is widely used in the beverage, food, and fragrance industries for its characteristic flavor profile. However, it chemically degrades over time in aqueous solutions due to an acid-catalyzed reaction, which leads to loss of desirable flavor notes and formation of off-flavor notes. The objective of this research was to examine the impact of organic phase composition [triacetin and medium-chain triacylglycerols (MCT)] on the oil-water partitioning and chemical degradation of citral in oil-in-water emulsions. MCT was present as emulsion droplets (d approximately 900 nm), whereas triacetin was present as microemulsion droplets (d approximately 10 nm). In the absence of organic phase, the rate of citral degradation increased as the aqueous phase pH was reduced from 7 to 3. The percentage of citral within the aqueous phase increased with increasing triacetin concentration at both pH 3 and 7, which was attributed to a reduction in MCT droplet concentration. There was no significant change in the particle size distribution of the emulsions during storage, independent of triacetin concentration and pH, which indicated that they were physically stable. Both 5 wt % MCT as emulsion droplets and 5 wt % triacetin as microemulsion droplets were able to appreciably slow citral degradation at pH 3. These results may have important implications for understanding and improving the chemical stability of citral in beverage emulsions.

Enhanced reductive dechlorination in columns treated with edible oil emulsion

The effect of edible oil emulsion treatment on enhanced reductive dechlorination was evaluated in a 14 month laboratory column study. Experimental treatments included: (1) emulsified soybean oil and dilute HCl to inhibit biological activity; (2) emulsified oil only; (3) emulsified oil and anaerobic digester sludge; and (4) continuously feeding soluble substrate. A single application of emulsified oil was effective in generating strongly reducing, anaerobic conditions for over 14 months. PCE was rapidly reduced to cis-DCE in all three live columns. Bioaugmentation with a halorespiring enrichment culture resulted in complete dechlorination of PCE to ethene in the soluble substrate column (yeast extract and lactate). However, an additional treatment with a pulse of yeast extract and bioaugmentation culture was required to stimulate complete dechlorination in the emulsion treated columns. Once the dechlorinating population was established, the emulsion only column degraded PCE from 90–120 μM to below detection with concurrent ethene production in a 33 day contact time. The lower biodegradation rates in the emulsion treated columns compared to the soluble substrate column suggest that emulsified oil barriers may require a somewhat longer contact time for effective treatment. In the HCl inhibited column, partitioning of PCE to the retained oil substantially delayed PCE breakthrough. However, reduction of PCE to more soluble degradation products ( cis-DCE, VC and ethene) greatly reduced the impact of oil–water partitioning in live columns. There was only a small decline in the hydraulic conductivity ( K) of column #1 (low pH + emulsion, K final/ K initial = 0.57) and column #2 (live + emulsion, K final/ K initial = 0.73) indicating emulsion injection did not result in appreciable clogging of the clayey sand. However, K loss was greater in column #3 (sludge +emulsion, K final/ K initial = 0.12) and column #4 (soluble substrate, K final/ K initial = 0.03) indicating clogging due to biomass and/or gas production can be significant.

Use of solid-phase microextraction for measuring oil–water partition coefficients and correlation with high-performance liquid chromatographic methods for lipophilicity

For flavour compounds, lipophilicity is often estimated by the partition coefficient between oil and water (log K oil–water), which is highly relevant to food. A modification of the shake-flask method is reported here where compounds are quantified in the two phases using solid-phase microextraction (SPME). SPME’s highly sensitivity to non-polar compounds facilitates quantification in the water phase. Twelve flavour compounds representing a broad range of lipophilicities and functional groups were analysed by two methods. Their log K oil–water was determined using SPME quantitation and their log k w using a reversed-phase HPLC methodology. The isocratic capacity factor at 60% methanol and predicted log P value also showed high correlation factors with other methods. The octadecyl silylated surface of the HPLC column provides a matrix that interacts with lipophilic compounds where the retention time is the indication of lipophilicity. Both methods gave reproducible results (median 3% and 4% RSD) and similar but not identical values for lipophilicity. The relationship between the two methods is log k w=0.85 log K oil–water+0.48 with a correlation coefficient of 0.94. The new SPME detection method, with the ability to quantify limonene and 2-pentylfuran at 1 ppm in the water phase, is preferred for flavour compound analysis due to the applicability of oil–water partitioning in food.

Nonanesthetic volatile drugs obey the Meyer-Overton correlation in two molecular protein site models.

Nonanesthetic volatile compounds fail to inhibit movement in response to noxious stimulation at concentrations predicted to induce anesthesia from their oil-water partitioning. Thus they represent tools to determine whether molecular models behave like the targets that mediate in vivo anesthetic actions. The effects of volatile anesthetics and nonanesthetics were examined in two experimental models in which anesthetics interact directly with proteins: the pore of the nicotinic acetylcholine receptor and human serum albumin. Wild-type mouse muscle nicotinic receptors and receptors containing pore mutations (alphaS252I + betaT263I) were studied electrophysiologically in membrane patches from Xenopus oocytes. Patch currents evoked by brief pulses of acetylcholine were measured in the presence of enflurane and two nonanesthetics, 1,2-dichlorohexafluorocyclobutane and 2,3-dichlorooctafluorobutane. Nonanesthetic interactions with human serum album were assessed by quenching of intrinsic protein fluorescence. Both anesthetic and nonanesthetic volatile compounds inhibited wild-type and alphaS252I + betaT263I mutant nicotinic channels but displayed different selectivity for open versus resting receptor states. Median inhibitory concentrations (IC50s) in wild-type nicotinic receptors were 870+/-20 microM for enflurane, 37+/-3 microM for 1,2-dichlorohexafluorocylcobutane, and 11.3+/-5.6 microM for 2,3-dichlorooctafluorobutane. For all three drugs, ratios of wild-type IC50s to mutant IC50mut ranged from 7-10, and ratios of wild-type IC50s to predicted anesthetic median effective concentrations (EC50s) ranged from 1.8-2.3. 1,2-Dichlorohexafluorocyclobutane quenched human serum albumin with an apparent dissociation constant (Kd) of 160+/-11 microM. The ratios of dissociation constants to predicted EC50s for the nonanesthetics were within a factor of two of the dissociation constant:EC50 ratios calculated for halothane and chloroform from previous published results. In two models in which anesthetics bind to protein sites, both anesthetic and nonanesthetic volatile drugs cause similar steady state effects with potencies that are predicted by hydrophobicity. These protein sites do not sterically discriminate between anesthetic and nonanesthetic drugs. However, differential state-selective actions on ion channel targets may underlie the distinct in vivo effects of anesthetics and nonanesthetics.

Pharmacokinetics of sparfloxacin in the serum and vitreous humor of rabbits: physicochemical properties that regulate penetration of quinolone antimicrobials.

We have used a recently described animal model to characterize the ocular pharmacokinetics of sparfloxacin in vitreous humor of uninfected albino rabbits following systemic administration and direct intraocular injection. The relationships of lipophilicity, protein binding, and molecular weight to the penetration and elimination of sparfloxacin were compared to those of ciprofloxacin, fleroxacin, and ofloxacin. To determine whether elimination was active, elimination rates following direct injection with and without probenecid or heat-killed bacteria were compared. Sparfloxacin concentrations were measured in the serum and vitreous humor by a biological assay. Protein binding and lipophilicity were determined, respectively, by ultrafiltration and oil-water partitioning. Pharmacokinetic parameters were characterized with RSTRIP, an iterative, nonlinear, weighted, least-squares-regression program. The relationship between each independent variable and mean quinolone concentration or elimination rate in the vitreous humor was determined by multiple linear regression. The mean concentration of sparfloxacin in the vitreous humor was 59.4% +/- 12.2% of that in serum. Penetration of sparfloxacin, ciprofloxacin, fleroxacin, and ofloxacin into, and elimination from, the vitreous humor correlated with lipophilicity (r2 > 0.999). The linear-regression equation describing this relationship was not improved by including the inverse of the square root of the molecular weight and/or the degree of protein binding. Elimination rates for each quinolone were decreased by the intraocular administration of probenecid. Heat-killed Staphylococcus epidermidis decreased the rate of elimination of fleroxacin. Penetration of sparfloxacin into the noninflamed vitreous humor was greater than that of any quinolone previously examined. There was an excellent correlation between lipophilicity and vitreous entry or elimination for sparfloxacin as well as ciprofloxacin, fleroxacin, and ofloxacin. There are two modes of quinolone translocation into and out of the vitreous humor: diffusion into the eye and both diffusion and carrier-mediated elimination out of the vitreous humor.