Pinus massoniana somatic embryo maturation, mycorrhization of regenerated plantlets and its resistance to Bursaphelenchus xylophilus.

Pine wilt disease, caused by the pine wood nematode (PWN, Bursaphelenchus xylophilus), is a major quarantine forest disease that poses a threat to various pine species, including Pinus massoniana (masson pine), worldwide. Breeding of PWN-resistant pine trees is an important approach to prevent the disease. To expedite the production of PWN-resistant P. massoniana accessions, we investigated the effects of maturation medium treatments on somatic embryo development, germination, survival, and rooting. Furthermore, we evaluated the mycorrhization and nematode resistance of regenerated plantlets. Abscisic acid was identified as the main factor affecting maturation, germination, and rooting of somatic embryos in P. massoniana, resulting in a maximum of 34.9 ± 9.4 somatic embryos per ml, 87.3 ± 9.1% germination rate, and 55.2 ± 29.3% rooting rate. Polyethylene glycol was identified as the main factor affecting the survival rate of somatic embryo plantlets, with a survival rate of up to 59.6 ± 6.8%, followed by abscisic acid. Ectomycorrhizal fungi inoculation with Pisolithus orientalis enhanced the shoot height of plantlets regenerated from embryogenic cell line (ECL) 20-1-7. Ectomycorrhizal fungi inoculation also improved the survival rate of plantlets during the acclimatization stage, with 85% of mycorrhized plantlets surviving four months after acclimatization in the greenhouse, compared with 37% non-mycorrhized plantlets. Following PWN inoculation, the wilting rate and the number of nematodes recovered from ECL 20-1-7 were lower than those recovered from ECL 20-1-4 and 20-1-16. The wilting ratios of mycorrhizal plantlets from all cell lines were significantly lower than those of non-mycorrhizal regenerated plantlets. This plantlet regeneration system and mycorrhization method could be used in the large-scale production of nematode-resistance plantlets and to study the interaction between nematode, pines, and mycorrhizal fungi.

Non-target and suspect-screening analyses of hydroponic soybeans and passive samplers exposed to different watershed irrigation sources.

Water scarcity increases the likelihood of irrigating food crops with municipal wastewater that may pose potential dietary risks of regulated and non-regulated organic chemical uptake to edible plant tissues. Only a few studies have used high resolution mass spectrometry (HRMS) to assess the uptake of chemicals of concern into food crops. This study used non-target and suspect-screening analyses to compare total chemical features, tentatively identified chemicals (TICs), and EPA ToxCast chemicals in soybean plants and passive samplers exposed to five different irrigation sources that were collected from an agricultural watershed during mild drought conditions. Secondary-treated municipal wastewater effluent, two surface waters, two ground waters, and deionized municipal tap water were used for two hydroponic experiments: soybean roots and shoots and Composite Integrative Passive Samplers (CIPS) harvested after fourteen days of exposure and soybeans after fifty-six days. CIPS were sealed in separate glass amber jars to evaluate their efficacy to mimic chemical features, TICs, and ToxCast chemical uptake in plant roots, shoots, and beans. Total soybean biomass and water use were greatest for tap water, municipal wastewater, and surface water downstream of the municipal wastewater facility relative to groundwater samples and surface water collected upstream of the wastewater facility. ToxCast chemicals were ubiquitous across watershed irrigation sources in abundance, chemical use category, and number. Wastewater-exposed soybeans had the fewest extractable TICs in plant tissues of all irrigation sources. More ToxCast chemicals were identified in CIPS than extracted from irrigation sources by solid phase extraction. ToxCast chemicals in beans and CIPS were similar in number, chemical use category, and log Kow range. CIPS appear to serve as a useful surrogate for ToxCast chemical uptake in beans, the edible food product.

Expanded coverage of non-targeted LC-HRMS using atmospheric pressure chemical ionization: a case study with ENTACT mixtures.

Non-targeted analysis (NTA) is a rapidly evolving analytical technique with numerous opportunities to improve and expand instrumental and data analysis methods. In this work, NTA was performed on eight synthetic mixtures containing 1264 unique chemical substances from the U.S. Environmental Protection Agency's Non-Targeted Analysis Collaborative Trial (ENTACT). These mixtures were analyzed by atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) using both positive and negative polarities for a total of four modes. Out of the 1264 ENTACT chemical substances, 1116 were detected in at least one ionization mode, 185 chemicals were detected using all four ionization modes, whereas 148 were not detected. Forty-four chemicals were detected only by APCI, and 181 were detected only by ESI. Molecular descriptors and physicochemical properties were used to assess which ionization type was preferred for a given compound. One ToxPrint substructure (naphthalene group) was found to be enriched in compounds only detected using APCI, and eight ToxPrints (e.g., several alcohol moieties) were enriched in compounds only detected using ESI. Examination of physicochemical parameters for ENTACT chemicals suggests that those with higher aqueous solubility preferentially ionized by ESI-. While ESI typically detects a larger number of compounds, APCI offers chromatograms with less background, fewer co-elutions, and additional chemical space coverage, suggesting both should be considered for broader coverage in future NTA research. Graphical abstract.

Effect of intra-articular administration of superparamagnetic iron oxide nanoparticles (SPIONs) for MRI assessment of the cartilage barrier in a large animal model.

Early diagnosis of cartilage disease at a time when changes are limited to depletion of extracellular matrix components represents an important diagnostic target to reduce patient morbidity. This report is to present proof of concept for nanoparticle dependent cartilage barrier imaging in a large animal model including the use of clinical magnetic resonance imaging (MRI). Conditioned (following matrix depletion) and unconditioned porcine metacarpophalangeal cartilage was evaluated on the basis of fluorophore conjugated 30 nm and 80 nm spherical gold nanoparticle permeation and multiphoton laser scanning and bright field microscopy after autometallographic particle enhancement. Consequently, conditioned and unconditioned joints underwent MRI pre- and post-injection with 12 nm superparamagnetic iron oxide nanoparticles (SPIONs) to evaluate particle permeation in the context of matrix depletion and use of a clinical 1.5 Tesla MRI scanner. To gauge the potential pro-inflammatory effect of intra-articular nanoparticle delivery co-cultures of equine synovium and cartilage tissue were exposed to an escalating dose of SPIONs and IL-6, IL-10, IFN-γ and PGE2 were assessed in culture media. The chemotactic potential of growth media samples was subsequently assessed in transwell migration assays on isolated equine neutrophils. Results demonstrate an increase in MRI signal following conditioning of porcine joints which suggests that nanoparticle dependent compositional cartilage imaging is feasible. Tissue culture and neutrophil migration assays highlight a dose dependent inflammatory response following SPION exposure which at the imaging dose investigated was not different from controls. The preliminary safety and imaging data support the continued investigation of nanoparticle dependent compositional cartilage imaging. To our knowledge, this is the first report in using SPIONs as intra-articular MRI contrast agent for studying cartilage barrier function, which could potentially lead to a new diagnostic technique for early detection of cartilage disease.

Lack of hydroxylated fullerene toxicity after intravenous administration to female Sprague-Dawley rats.

Hydroxylated fullerenes (C60OH(x)) or fullerols are water-soluble carbon nanoparticles that have been explored for potential therapeutic applications. This study assesses acute in vivo tolerance in 8-wk-old female Sprague-Dawley rats to intravenous (iv) administration of 10 mg/kg of well-characterized C60(OH)30. Complete histopathology and clinical chemistries are assessed at 8, 24, and 48 h after dosing. Minor histopathology changes are seen, primarily in one animal. No clinically significant chemistry changes were observed after treatment. These experiments suggest that this fullerol was well tolerated after iv administration to rats.

An index for characterization of nanomaterials in biological systems.

In a physiological environment, nanoparticles selectively absorb proteins to form 'nanoparticle-protein coronas', a process governed by molecular interactions between chemical groups on the nanoparticle surfaces and the amino-acid residues of the proteins. Here, we propose a biological surface adsorption index to characterize these interactions by quantifying the competitive adsorption of a set of small molecule probes onto the nanoparticles. The adsorption properties of nanomaterials are assumed to be governed by Coulomb forces, London dispersion, hydrogen-bond acidity and basicity, polarizability and lone-pair electrons. Adsorption coefficients of the probe compounds were measured and used to create a set of nanodescriptors representing the contributions and relative strengths of each molecular interaction. The method successfully predicted the adsorption of various small molecules onto carbon nanotubes, and the nanodescriptors were also measured for 12 other nanomaterials. The biological surface adsorption index nanodescriptors can be used to develop pharmacokinetic and safety assessment models for nanomaterials.

Evaluation of perfused porcine skin as a model system to quantitate tissue distribution of fullerene nanoparticles.

Nanomaterials are increasingly playing a role in society for uses ranging from biomedicine to microelectronics, however pharmacokinetic studies, which will be necessary for human health risk assessments, are limited. Tissue distribution, one component of pharmacokinetics, can be assessed by quantifying arterial extraction of materials in an isolated perfused porcine skin flap (IPPSF). The objective of this study was to assess the IPPSF as a model system to quantitate the distribution of fullerene nanoparticles (nC(60)) from the vascular space into tissues. IPPSFs were perfused for 4h with 0.885 microg/mL nC(60) in media with immunoglobulin G present (IgG(+)) or absent (IgG(-)) followed by a 4h perfusion with media only during a washout phase. Arterial and venous concentrations of nC(60) were measured in the media by HPLC-UV/vis chromatography. Steady state differences in the arterial and venous nC(60) concentrations were compared to determine extraction from the vascular space of the IPPSF, and the venous nC(60) concentration versus time profiles were used to calculate compartmental pharmacokinetic parameters. The steady state differences in the arterial and venous concentrations in the IPPSF were small with extraction percentages (mean+/-sd) of 8.2+/-5.7% and 4.2+/-6.7% for IgG(+) and IgG(-) media, respectively, and were not significantly different between the types of media. The venous concentrations of nC(60) in both types of media were best fit with a 2 compartment model with terminal half lives (harmonic mean) of 17.5 and 28.0 min for IgG(+) and IgG(-) media, respectively. The apparent volumes of distribution at steady state were 0.12+/-0.047 and 0.10+/-0.034 L/kg, for IgG(+) and IgG(-) media, respectively. By 4 h following infusion of nC(60), the recovery of nC(60) in the venous effluent was 94+/-5.5% and 97+/-6.8% of the infused nC(60) for IgG(+) and IgG(-) media, respectively. Based on the apparent volume of distribution, the low extraction during the perfusion, and the high percentage recovery following the washout phase, there was limited distribution of nC(60) from the vascular space into the extracellular space and negligible intracellular uptake of nC(60) in this system.

Application of linear solvation energy relationships to a custom-made polyaniline solid-phase microextraction fiber and three commercial fibers.

The term linear solvation energy relationships, LSERs, is considered to be a specific subset of a larger group of thermodynamic relationships called linear free energy relationships. Overall, the LSERs model represents a three-step thermodynamic process. The most recently accepted notation for the LSER equation, proposed by Abraham is given as follows: SP= c+eE+sS+aA+bB+vV where SP is any free energy related property of a solute, such as log K, and each term in the equation represents a specific type of chemical interaction. In this work, LSERs were applied to a custom-made polyaniline (PANI) solid-phase microextraction fiber and three commercial fibers immersed in water in order to aid in the assessment of a diverse series of solutes' partitioning behavior. By experimentally determining the log K for a series of solutes with known solute descriptors (E, S, A, B, and V) and performing multi-linear regression, the unknown system coefficients (e, s, a, b, and v) were obtained. The sign and magnitude of the system coefficients reflect the relative strengths of chemical interactions that affect partitioning between the two phases (fiber and water). The LSER study showed that the system properties having the greatest influence on log K were ease of cavity formation and hydrogen bond donating ability. The differences in dipolarity/polarizability as well as in hydrogen bond accepting ability further showed that all four fibers offer a unique environment for solute partitioning. The PANI fiber may offer greater flexibility in the choice of fibers to use for solid-phase microextraction.

Quantification of chemical mixture interactions modulating dermal absorption using a multiple membrane fiber array.

Dermal exposures to chemical mixtures can potentially increase or decrease systemic bioavailability of toxicants in the mixture. Changes in dermal permeability can be attributed to changes in physicochemical interactions between the mixture, the skin, and the solute of interest. These physicochemical interactions can be described as changes in system coefficients associated with molecular descriptors described by Abraham's linear solvation energy relationship (LSER). This study evaluated the effects of chemical mixtures containing either a solvent (ethanol) or a surfactant (sodium lauryl sulfate, SLS) on solute permeability and partitioning by quantifying changes in system coefficients in skin and a three-membrane-coated fiber (MCF) system, respectively. Regression analysis demonstrated that changes in system coefficients in skin were strongly correlated ( R2 = 0.89-0.98) to changes in system coefficients in the three-membrane MCF array with mixtures containing either 1% SLS or 50% ethanol. The PDMS fiber appeared to play a significant role (R2 = 0.84-0.85) in the MCF array in predicting changes in solute permeability, while the WAX fiber appeared to contribute less (R2 = 0.59-0.77) to the array than the other two fibers. On the basis of changes in system coefficients that are part of a LSER, these experiments were able to link physicochemical interactions in the MCF with those interactions in skin when either system is exposed to 1% SLS or 50% ethanol. These experiments further demonstrated the utility of a MCF array to adequately predict changes in dermal permeability when skin is exposed to mixtures containing either a surfactant or a solvent and provide some insight into the nature of the physiochemical interactions that modulate dermal absorptions.

Partitioning behavior of aromatic components in jet fuel into diverse membrane-coated fibers.

Jet fuel components are known to partition into skin and produce occupational irritant contact dermatitis (OICD) and potentially adverse systemic effects. The purpose of this study was to determine how jet fuel components partition (1) from solvent mixtures into diverse membrane-coated fibers (MCFs) and (2) from biological media into MCFs to predict tissue distribution. Three diverse MCFs, polydimethylsiloxane (PDMS, lipophilic), polyacrylate (PA, polarizable), and carbowax (CAR, polar), were selected to simulate the physicochemical properties of skin in vivo. Following an appropriate equilibrium time between the MCF and dosing solutions, the MCF was injected directly into a gas chromatograph/mass spectrometer (GC-MS) to quantify the amount that partitioned into the membrane. Three vehicles (water, 50% ethanol-water, and albumin-containing media solution) were studied for selected jet fuel components. The more hydrophobic the component, the greater was the partitioning into the membranes across all MCF types, especially from water. The presence of ethanol as a surrogate solvent resulted in significantly reduced partitioning into the MCFs with discernible differences across the three fibers based on their chemistries. The presence of a plasma substitute (media) also reduced partitioning into the MCF, with the CAR MCF system being better correlated to the predicted partitioning of aromatic components into skin. This study demonstrated that a single or multiple set of MCF fibers may be used as a surrogate for octanol/water systems and skin to assess partitioning behavior of nine aromatic components frequently formulated with jet fuels. These diverse inert fibers were able to assess solute partitioning from a blood substitute such as media into a membrane possessing physicochemical properties similar to human skin. This information may be incorporated into physiologically based pharmacokinetic (PBPK) models to provide a more accurate assessment of tissue dosimetry of related toxicants.

Membrane-coated fiber array approach for predicting skin permeability of chemical mixtures from different vehicles.

A membrane-coated fiber (MCF) array approach was developed for quantitative assessment of skin absorption from chemical mixtures, which was based on the similarity in the absorption mechanisms of the MCF membrane and the stratum corneum of the skin. A set of probe compounds were used to detect the relative molecular interaction strengths of chemicals with the vehicle and the membranes, which provided a linkage between the skin permeability (log k) and MCF partition coefficients (log KF). A predictive model was established via multiple linear regression analysis of the data matrix of experimentally measured log k value and log KFm values; log k=a0+a1 log KF1+a2 log KF2+...+an log KFm, where m is the number of diverse MCFs. Twenty-five probe compounds and three MCFs (polydimethylsiloxane for lipophilic, polyacrylate for polarizable, and CarboWax for polar interactions) were used to demonstrate the model development processes in the MCF array approach. The skin permeability of the probe compounds was measured with conventional diffusion cell experiments using dermatomed porcine skin. Three predictive models were established for skin permeability prediction from chemical mixtures in water, 50% ethanol, and 1% sodium lauryl sulfate (SLS) with R2 values of 93, 91, and 83, respectively. The log k and log KF values were considerably altered by the addition of ethanol or SLS into the dose vehicle; however, their correlations to skin permeability remained strong under various conditions. These results suggested that the experimentally based MCF array approach can be used to predict skin absorption from chemical mixtures in different vehicles or formulations.

An experimentally based approach for predicting skin permeability of chemicals and drugs using a membrane-coated fiber array.

A membrane-coated fiber (MCF) array approach is proposed for predicting the percutaneous absorption of chemicals and drugs from chemical or biological mixtures. Multiple MCFs were used to determine the partition coefficients of compounds (logK(MCF)). We hypothesized that one MCF will characterize one pattern of molecular interactions and therefore the skin absorption process can be simulated by a multiple MCF array having diverse patterns of molecular interactions. Three MCFs, polydimethylsiloxane (PDMS), polyacrylate (PA) and CarboWax (Wax), were used to determine the logK(MCF) values for a set of calibration compounds. The skin permeability log(kp) of the compounds was measured by diffusion experiments using porcine skin. The feasibility of the MCF array approach for predicting skin permeability was demonstrated with the three MCFs. A mathematical model was established by multiple linear regression analysis of the log(kp) and logK(MCF) data set: log(kp)=-2.34-0.124 logK(pdms)+1.91 logK(pa)-1.17 logK(wax) (n=25, R(2)=0.93). The MCF array approach is an alternative animal model for skin permeability measurement. It is an experimentally based, high throughput approach that provides high prediction confidence and does not require literature data nor molecular structure information in contrast to the existing predictive models.

Regression method of the hydrophobicity ruler approach for determining octanol/water partition coefficients of very hydrophobic compounds.

A regression method was developed for the hydrophobicity ruler approach, which is an indirect method for determining the octanol/water partition coefficients of very hydrophobic compounds. Two constants introduced into the mathematical model were obtained by regression of the absorption data sampled before the partition equilibrium. A water miscible organic solvent was used to increase the solubility of the very hydrophobic compounds in the aqueous solution so that the hydrophobicity scale was reduced and the equilibration was accelerated. Polydimethylsiloxane/methanol aqueous solution and a series of 21 polychlorinated biphenyls (PCBs) were used to demonstrate the regression method. The PCB compounds with known experimental logK(o/w) values served as reference compounds, while the PCB compounds without known logK(o/w) values were determined. The distribution coefficients (logK(p/s)), uptake and elimination rate constants were obtained from the two regression constants for each compound (reference or unknown). The correlation of the logK(p/s) values of the reference PCB compounds with their logK(o/w) values was linear (logK(o/w)=2.69logK(p/s)+0.76, R(2)=0.97). The logK(o/w) values were compared with literature values and suggested that some values from the literature far off the calibration line could be inaccurate. The critical experimental factors, the merits of the regression method were discussed.

Trace analysis of fullerenes in biological samples by simplified liquid-liquid extraction and high-performance liquid chromatography.

Fullerene (C60) has several potential biomedical and industrial applications. While pure fullerene is not soluble in water, nanoparticles of the fullerene aggregates (nano-C60) can be prepared in water solutions. The concentration of nano-C(60) in biological media after systemic exposure could be very low and requires trace analytical methods to be developed for the toxicological and pharmacokinetic studies of the nanomaterial. A serious drop in extraction efficiency was observed when the concentration was under 0.5 microg/mL using traditional liquid-liquid extraction (LLE) protocols. The evaporation of the solvent extract to dryness was found to be the main reason for the efficiency drop and an improved evaporation method was proposed to overcome this problem. Optimal proportion of glacial acetic acid (GAA) was used to solublize the proteins and surfactants in the biological samples, so that the emulsion problem was eliminated during LLE. Magnesium perchlorate was used to destabilize the nano-C60 particles in the water solution and promoted the solvent extraction. A simplified LLE method was developed for high throughput while preserved the advantages of the traditional LLE. The developed method was used for trace analysis of fullerenes in protein containing media and tape-stripped skin samples. Under optimal experimental conditions, the detection limit was 0.34 ng/mL and the recovery was in the range of 94-100% (n=5) at a concentration of 10 ng/mL nano-C60 in the biological media.

Novel hydrophobicity ruler approach for determining the octanol/water partition coefficients of very hydrophobic compounds via their polymer/solvent solution distribution coefficients.

A novel hydrophobicity ruler approach for determining the octanol/water partition coefficients of very hydrophobic compounds is proposed, which is an indirect method that measures the polymer/solvent solution distribution coefficients (log Kp/s) of reference and unknown compounds. The log Kp/s values of the unknown compounds can be calibrated to their log Ko/w values via the correlation of the log Kp/s values of the reference compounds with their log Ko/w values. An organic solvent was used to increase the solubility of the very hydrophobic compounds in the aqueous solution, so that their concentrations and absorption amounts were high enough to be measured precisely. The solvent also reduced the hydrophobicity scale of the very hydrophobic compounds and controlled the amounts absorbed into the polymer phase, so that compounds spanning a very wide range of log Ko/w values could be measured in a single measurement and the coexisting compounds would not interfere each other. Poly(dimethylsiloxane) (PDMS), aqueous methanol solutions, and a series of 21 PCB (polychlorinated biphenyl) compounds were used to demonstrate the principle of the hydrophobicity ruler approach. The PCB compounds with known experimental log Ko/w values served as reference compounds, whereas the PCB compounds without known log Ko/w values were determined. The log Ko/w values determined for PCB126, PCB187, PCB197, PCB180, PCB170, and PCB195 were 6.94, 7.84, 8.33, 8.17, 7.92, and 8.49, respectively. The correlation of the log Kp/s values of the reference PCB compounds with their log Ko/w values was linear (log Ko/w=2.56 log Kp/s+1.08, R2=0.95). The hydrophobicity ruler approach is also a valuable tool for validating the experimental and theoretical log Ko/w values and identifying outliers in log Ko/w databases.

Determination of the partition coefficients and absorption kinetic parameters of chemicals in a lipophilic membrane/water system by using a membrane-coated fiber technique.

The absorption kinetics of chemicals in a lipophilic membrane/water system was studied with a membrane-coated fiber (MCF) technique, in which the partition coefficient, membrane diffusivity and boundary layer adjacent to the membrane were taken into account. The cumulative amount permeated into the membrane was expressed as a function of absorption time in an exponential equation. Two constants were introduced into the model. Both of them were clearly defined by the physiochemical parameters of the system and were obtained by regression of the experimental data sampled over a limited time. The partition and diffusion coefficients, as well as the thickness of the boundary layer, were calculated from the two constants. The kinetic model adequately described the absorption kinetics of the MCF technique. All of the theoretical predictions were supported by the experimental results. The measured partition coefficients correlated well with the published octanol/water partition coefficient (R(2)=0.91). The thickness of the boundary layer was 5.2 microm in a solution stirred at 400 rpm. An inference of the kinetic model revealed that the contribution of the boundary layer to the absorption kinetics is significant for lipophilic chemicals by a lipophilic membrane. It suggested that the absorption rate of a very lipophilic compound could be controlled by the boundary layer even though the diffusivity of the compound in the membrane is lower than that in the solution. It was demonstrated that the MCF technique could be used to determine the partition, diffusion and permeation coefficients, as well as the thickness of the boundary layer in a lipophilic membrane/water system.

Membrane uptake kinetics of jet fuel aromatic hydrocarbons from aqueous solutions studied by a membrane-coated fiber technique.

The absorption of aromatic hydrocarbons from aqueous media is a critical step involved in many biological processes after occupational and environmental exposures to jet fuel. A membrane-coated fiber (MCF) technique was used to study the uptake kinetics. A flow-through system was used to provide a constant concentration for the prolonged permeation experiments. Polydimethylsiloxane (PDMS) and polyacrylate (PA) MCFs were used to study the differential absorptivity of the aromatic compounds between the two membrane materials. The equilibrium absorption amount and a kinetic parameter describing the absorption kinetics were obtained by the regression of the permeation profiles of the aromatic compounds with a mathematical model. The partition coefficients, uptake, and elimination rate constants were determined for six benzene and three naphthalene derivatives. The PDMS/water partition coefficients of the benzene and naphthalene derivatives were linearly correlated with their logK(o/w) (LogK(pdms/w) = 0.871LogK(o/w) - 0.241, R(2) = 0.995). The PA/water partition coefficients of the benzene derivatives and the naphthalene derivatives were correlated differently with their logK(o/w). The correlation equations for benzene and naphthalene derivatives were LogK(pa/w) = 0.865LogK(o/w) + 0.0045, R(2) = 0.997 and LogK(pa/w) = 0.763LogK(o/w) + 0.911, R(2) = 1.00, respectively. These results suggest that the MCF technique can detect subtle differences in molecular interactions of the two group derivatives between the two membrane/water systems and may be used to study the absorption and permeation properties of closely related compounds. Finally, the regression method is a particularly useful tool to determine partition coefficients of very lipophilic compounds.

A compartment model for the membrane-coated fiber technique used for determining the absorption parameters of chemicals into lipophilic membranes.

PURPOSE: The purpose of this work was to develop a compartment model for the membrane-coated fiber (MCF) technique for determining the absorption parameters of chemicals into lipophilic membranes. METHODS: A polymer membrane coated onto a section of inert fiber was used as a permeation membrane in the MCF technique. When MCFs were immersed into a donor solution, the compounds in the solution partitioned into the membrane. At a given permeation time, a fiber was removed from the solution and transferred into a gas chromatography injector for quantitative analysis. The permeation process of a given chemical from the donor phase into the membrane was described by a one-compartment model by assuming first-order kinetics. RESULTS: A mathematical model was obtained that describes the cumulative amount of a chemical permeated into the membrane as a function of the permeation time in an exponential equation. Two constants were introduced into the compartment model that were clearly defined by the physiochemical parameters of the system (a kinetic parameter and the equilibrium absorption amount) and were obtained by regression of the experimental data sampled over a limited time before equilibrium. The model adequately described the permeation kinetics of the MCF technique. All theoretical predictions were supported by the experimental results. The experimental data correlated well with the mathematical regression results. The partition coefficients, initial permeation rate, uptake, and elimination rate constants were calculated from the two constants. CONCLUSIONS: The compartment model can describe the absorption kinetics of the MCF technique. The regression method based on the model is a useful tool for the determination of the partition coefficients of lipophilic compounds when it takes too long for them to reach permeation equilibrium. The kinetic parameter and the initial permeation rate are unique parameters of the MCF technique that could be used in the development of quantitative structure-activity relationship models.

A novel in-vitro technique for studying percutaneous permeation with a membrane-coated fiber and gas chromatography/mass spectrometry: part I. Performances of the technique and determination of the permeation rates and partition coefficients of chemical mixtures.

PURPOSE: To develop a novel in-vitro technique for rapid assessment of percutaneous absorption of chemical mixtures. METHODS: A silastic membrane was coated on to a fiber to be used as a permeation membrane. The membrane-coated fiber was immersed in the donor phase to partition the compounds into the membrane. At a given partition time, the membrane-coated fiber was transferred into a GC injector to evaporate the partitioned compounds for quantitative and qualitative analyses. RESULTS: This technique was developed and demonstrated to study the percutaneous permeation of a complex mixture consisting of 30 compounds. Each compound permeated into the membrane was identified and quantified with GC/MS. The standard deviation was less than 10% in 12 repeated permeation experiments. The partition coefficients and permeation rates in static and stirred donor solution were obtained for each compound. The partition coefficients measured by this technique were well correlated (R2 = 0.93) with the reported octanol/water partition coefficients. CONCLUSIONS: This technique can be used to study the percutaneous permeation of chemical mixtures. No expensive radiolabeled chemicals are required. Each compound permeated into the membrane can be identified and quantified. The initial permeation rate and equilibrium time can be obtained for each compound, which could serve as characteristic parameters regarding the skin permeability of the compound.

A simplified liquid-solid extraction technique for the analyses of pesticide residues in soil samples.

A simplified liquid-solid extraction technique was studied for the analyses of pesticide residues in soil samples. It is a simple, one step sample preparation method based on a relative quantification concept. Linear response curves were obtained for all of the target compounds regardless of their surface adsorption. This observation was explained and modeled to obey Langmuir adsorption Equation. The adsorption of analytes onto the sample surfaces will sacrifice the detection sensitivity. The strategies to reduce the surface adsorption, such as, molecular replacement and selection of solvents, were discussed. The relative quantification and the wide varieties of available solvents would enable the technique to be a useful method for the monitoring and analyses of pesticide residues in soils.