Partition Coefficients Of Analytes Research Articles

Solvent-induced modulation of the chemical sensing performance of gold nanoparticle film chemiresistors

The analyte sensitivity of a chemical sensor is commonly tuned by the type of chemical recognition element. Here, it is shown that the solvent also plays a critical role in the sensing performance of thiol-capped gold nanoparticle film chemiresistors. Both the resistance change and speed of response of the chemiresistor can be optimised by adjusting the composition of methanol and water used for detection of the pesticide permethrin. It is shown that the resistance change is governed by the partitioning of the analyte between the thiol coating of the gold nanoparticles and the solvent. The partition coefficient, log P, has a strong influence on the response magnitude and is directly correlated to the response time. By varying the solvent, the log P of extremely high partitioning analytes such as permethrin in water can be lowered, and a much larger resistance change can be obtained in a shorter time period (5 min). A theoretical model is developed that correlates the experimental findings to changes in analyte partition coefficient with solvent type and composition. The results have significant implications for the design of chemical sensors and solvent conditions that can offer an enhanced signal within a practical timeframe.

QSAR studies on partition coefficients of organic compounds for polydimethylsiloxane of solid-phase microextraction devices

The solid-phase microextraction (SPME) technique has been widely applied to sample the environmental matrices for organic compounds. The success of employing SPME requires knowledge of the coating-matrix partition coefficients of analytes. Polydimethylsiloxane (PDMS) is the most widely used polymeric coating for the SPME device. In this study, the quantitative structure activity relationships (QSAR) for the PDMS-water (K fw ) and PDMS-gas partition coefficients (K fg ) of organic compounds were established using E-Dragon software and multiple linear regression analysis. K fw was significantly correlated to the BLTA96 descriptor, implying that the PDMS-water partition coefficients were primarily determined by the polarity of analyte molecules. In addition, K fg was significantly dependent on the Harary H index, i.e., molecular connectivity index or polarizability, of the organic compounds. If the organic compounds were grouped in alkanes and aromatic hydrocarbons, K fw and K fg were well proportional to their octanol–water partition coefficients. The statistical results of internal and external validation, determined by the square of the coefficient of multiple correlation (R 2 ≥ 0.865) and the leave-one-out cross-validation (Q 2 ≥ 0.751), showed that the QSAR models developed herein have good stability and great predictive power among the molecular descriptors and SPME/PDMS partition coefficients. The results of this study will facilitate the practical applications of SPME as a greener methodology.

Separation of cucurbitane triterpenoids from bitter melon drinks and determination of partition coefficients using vortex-assisted dispersive liquid-phase microextraction followed by UHPLC analysis.

A rapid, effective method applying vortex-assisted liquid-liquid microextraction before ultra-high performance liquid chromatography with mass spectrometry and evaporative light scattering detection was developed for the analysis of four cucurbitane triterpenoids (momordicoside L, momordicoside K, momordicoside F2 , and 3β,7β,25-trihydroxy cucurbita-5,23(E)-dien-19-al) in bitter melon juices. Variables affecting the extraction efficiency including different extraction solvents, volume of extraction solvent, salt amount, acid condition, vortex speed and time were optimized thoroughly. Under the optimum conditions, precision was determined by the intra- and inter-day tests in a range of 1.1-5.7% and 2.9-4.0% (RSD), respectively, with recoveries between 95.7 and 106.1%. The calibration curves showed good linearity with square correlation coefficient of 0.9936-0.9991 (evaporative light scattering detection) and 0.9858-0.9989 (MS). The detection limits ranged from 0.8-1.9ng/mL (MS) to 3-10ng/mL (evaporative light scattering detection) for these compounds. Enrichment factors of four target compounds were between 27 and 63 times. The proposed method was also used to determine the apparent solvent/water partition coefficients of analytes within the range of 53-120. The developed method can effectively enrich and quantify cucurbitane triterpenoids from bitter melon drinks.

Introduction of Fullerene as a New Carrier in Electromembrane Extraction for the Determination of Ibuprofen and Sodium Diclofenac as Model Acidic Drugs in Real Urine Samples

Introducing new additives in supported liquid membrane (SLM) as carriers is an interesting and debatable issue in the field of microextraction methods, especially in electro membrane extraction (EME). In this study, C60 fullerene was used as a new carrier in the SLM, and EME followed by high-performance liquid chromatography coupled with ultraviolet detection was optimized and validated for the quantification of ibuprofen and sodium diclofenac as two model acidic drugs. Optimized conditions for extraction of the mentioned drugs from 4.0 mL aqueous sample were obtained as follows: 1-octanol containing 0.6% (w/v) C60 fullerene as the SLM, potential difference of 6 V, 28 min as the extraction time, 12.8 as the acceptor phase pH value and 10.5 as the donor phase pH value. Under the optimized conditions, the enrichment factors were obtained within the range of 166–188, which corresponds to extraction recoveries of 83–94%. The limits of detection and quantification were in the range of 5–10 and 15–30 ng mL−1, respectively. To understand the influence of C60 fullerene on extraction efficiency, a comparative study was carried out between conventional EME and modified EME methods. The results showed that the presence of C60 fullerene in the SLM increased the overall analyte partition coefficient in the membrane and, therefore, led to an enhancement in analyte transport. Finally, the applicability of this method was evaluated by the extraction and determination of these drugs in real urine samples.

An Efficient Liquid-Phase Microextraction Method Combined with UHPLC-ELSD/MS for Analysis of Cucurbitane Triterpenoids in Bitter Melon Drinks

Momordica charantia L. of family Cucurbitaceae, also known as bitter melon, is a tropical and subtropical vine grown in Asia and Africa. Earlier studies showed that cucurbitane-type triterpenoids were the major active constituents responsible for the hypoglycemic effects exerted by M. charantia [1]. Liquid-phase microextraction is an efficient tool to extract and concentrate analytes of interest from complex matrices, such as plant, medicine, and bio-samples in recent years [2]. In the present work, a simple and effective vortex-assisted dispersive microextraction method is developed for extraction and concentration of cucurbitane triterpenoids (Momordicoside L, Momordicoside K, Momordicoside F2, and 3β,7β,25-trihydroxy cucurbita-5, (23E)-dien-19al) in bitter melon drinks prior to the determination by UPLC-ELSD/MS. Different solvents, volume of extract solvent, pH range, salt amount, and other variables influencing extraction efficiency were optimized. Recoveries and precision were tested with satisfactory results under the optimum conditions. Enrichment factors of 27 to 63-fold were obtained for four compounds. The apparent solvent/water partition coefficients of analytes were calculated within the range of 53 – 120. The proposed method can effectively enrich and quantitate cucurbitane triterpenoids from bitter melon drinks.

Qualitative and quantitative evaluation of solvent systems for countercurrent separation

Rational solvent system selection for countercurrent chromatography and centrifugal partition chromatography technology (collectively known as countercurrent separation) studies continues to be a scientific challenge as the fundamental questions of comparing polarity range and selectivity within a solvent system family and between putative orthogonal solvent systems remain unanswered. The current emphasis on metabolomic investigations and analysis of complex mixtures necessitates the use of successive orthogonal countercurrent separation (CS) steps as part of complex fractionation protocols. Addressing the broad range of metabolite polarities demands development of new CS solvent systems with appropriate composition, polarity (π), selectivity (σ), and suitability. In this study, a mixture of twenty commercially available natural products, called the GUESSmix, was utilized to evaluate both solvent system polarity and selectively characteristics. Comparisons of GUESSmix analyte partition coefficient (K) values give rise to a measure of solvent system polarity range called the GUESSmix polarity index (GUPI). Solvatochromic dye and electrical permittivity measurements were also evaluated in quantitatively assessing solvent system polarity. The relative selectivity of solvent systems were evaluated with the GUESSmix by calculating the pairwise resolution (αip), the number of analytes found in the sweet spot (Nsw), and the pairwise resolution of those sweet spot analytes (αsw). The combination of these parameters allowed for both intra- and inter-family comparison of solvent system selectivity. Finally, 2-dimensional reciprocal shifted symmetry plots (ReSS2) were created to visually compare both the polarities and selectivities of solvent system pairs. This study helps to pave the way to the development of new solvent systems that are amenable to successive orthogonal CS protocols employed in metabolomic studies.

Determination of solid–liquid partition coefficient of volatile compounds by solid phase ratio variation based headspace analysis

A novel method has been developed for the determination of the solid–liquid partition coefficient of volatile analytes using headspace gas chromatography (HS–GC). The method is based on the headspace measurement for the three-phase equilibrium in sample vials containing different amounts of solid sample. Theory is presented that allows calculation of partition coefficient of the analyte from the HS–GC data obtained at the condition of solid phase ratio variation (SPRV). Analysis of errors demonstrates that this solid phase ratio variation method generates results with reasonable precision for all volatile compounds, much better than the liquid-focused (i.e., liquid phase ratio variation) method reported early.The solid phase ratio variation method was used to determine the solid–liquid partition coefficient of toluene in a water–polystyrene system, using polymer particles with average size ranging from 0.4 to 2.1μm. The results show that the partition coefficient of toluene in the given system is proportional to the specific surface area of the polymer particles, as expected.In summary, the method is a simple and practical tool for determining the solid–liquid partition coefficient of volatile analytes.

Polymeric ionic liquid coatings versus commercial solid-phase microextraction coatings for the determination of volatile compounds in cheeses

The extraction performance of four polymeric ionic liquid (PIL)-based solid-phase microextraction (SPME) coatings has been studied and compared to that of commercial SPME coatings for the extraction of 16 volatile compounds in cheeses. The analytes include 2 free fatty acids, 2 aldehydes, 2 ketones and 10 phenols and were determined by headspace (HS)-SPME coupled to gas chromatography (GC) with flame-ionization detection (FID). The PIL-based coatings produced by UV co-polymerization were more efficient than PIL-based coatings produced by thermal AIBN polymerization. Partition coefficients of analytes between the sample and the coating (Kfs) were estimated for all PIL-based coatings and the commercial SPME fiber showing the best performance among the commercial fibers tested: carboxen-polydimethylsyloxane (CAR-PDMS). For the PIL-based fibers, the highest K(fs) value (1.96 ± 0.03) was obtained for eugenol. The normalized calibration slope, which takes into account the SPME coating thickness, was also used as a simpler approximate tool to compare the nature of the coating within the determinations, with results entirely comparable to those obtained with estimated K(fs) values. The PIL-based materials obtained by UV co-polymerization containing the 1-vinyl-3-hexylimidazolium chloride IL monomer and 1,12-di(3-vinylimiazolium)dodecane dibromide IL crosslinker exhibited the best performance in the extraction of the select analytes from cheeses. Despite a coating thickness of only 7 µm, this copolymeric sorbent coating was capable of quantitating analytes in HS-SPME in a 30 to 2000 µg L(-1) concentration range, with correlation coefficient (R) values higher than 0.9938, inter-day precision values (as relative standard deviation in %) varying from 6.1 to 20%, and detection limits down to 1.6 µg L(-1).

A new method for the enhancement of electromembrane extraction efficiency using carbon nanotube reinforced hollow fiber for the determination of acidic drugs in spiked plasma, urine, breast milk and wastewater samples

A new design of low voltage electromembrane extraction (EME) using carbon nanotube reinforced hollow fiber was developed for the determination of acidic drugs in biological and wastewater samples. The supported liquid membrane (SLM) with carbon nanotubes as the sorbent interface was used in this research. CNTs have large surface area and high adsorption capacity for a wide range of organic and inorganic species. Therefore, the presence of CNTs in SLM increased the overall analyte partition coefficient in the membrane and lead to enhancement in analyte transport. Optimization of the variables affecting this method was carried out in order to achieve the best extraction efficiency. Ibuprofen and naproxen, nonsteroid anti-inflammatory drugs (NSAIDs), were selected as model acidic drugs. Optimal extractions were accomplished with 1-octanol with 3.0mgmL−1 CNTs as the SLM, with 5V as the driving force, and with pH 7.4 in donor and pH 12 in acceptor solutions. Equilibrium extraction conditions were obtained after 10min of operation with the whole assembly agitated at 500rpm. Under the optimized extraction conditions, the proposed EME technique provided good linearity (>0.998), repeatability (RSD=2.7–3.2), low limits of detection (1–3ngmL−1), excellent preconcentration (PF=180–188) and high recoveries (90–94%). In comparison with the conventional EME method, this method showed better results (lower voltage, higher preconcentration factors and higher recoveries). Finally, the developed method was successfully used for the determination of ibuprofen and naproxen in different spiked matrices including plasma, urine, breast milk and wastewater samples.

Analysis of Some Biogenic Amines by Micellar Liquid Chromatography

Micellar liquid chromatography (MLC) with the use of high performance liquid chromatography (HPLC) was used to determine some physicochemical parameters of six biogenic amines: adrenaline, dopamine, octopamine, histamine, 2-phenylethylamine, and tyramine. In this paper, an influence of surfactant’s concentration and pH of the micellar mobile phase on the retention of the tested substances was examined. To determine the influence of surfactant’s concentration on the retention of the tested amines, buffered solutions (at pH 7.4) of ionic surfactant—sodium dodecyl sulfate SDS (at different concentrations) with acetonitrile as an organic modifier (0.8/0.2 v/v) were used as the micellar mobile phases. To determine the influence of pH of the micellar mobile phase on the retention, mobile phases contained buffered solutions (at different pH values) of sodium dodecyl sulfate SDS (at 0.1 M) with acetonitrile (0.8/0.2 v/v). The inverse of value of retention factor () versus concentration of micelles () relationships were examined. Other physicochemical parameters of solutes such as an association constant analyte—micelle ()—and partition coefficient of analyte between stationary phase and water (hydrophobicity descriptor) () were determined by the use of Foley’s equation.

Characterization of the gas sensors based on polymer-coated resonant microcantilevers for the detection of volatile organic compounds

The gas sensors based on polymer-coated resonant microcantilevers for volatile organic compounds (VOCs) detection are investigated. A method to characterize the gas sensors through sensor calibration is proposed. The expressions for the estimation of the characteristic parameters are derived. The effect of the polymer coating location on the sensor's sensitivity is investigated and the formula to calculate the polymer–analyte partition coefficient without knowing the polymer coating features is presented for the first time. Three polymers: polyethyleneoxide (PEO), polyethylenevinylacetate (PEVA) and polyvinylalcohol (PVA) are used to perform the experiments. Six organic solvents: toluene, benzene, ethanol, acetone, hexane and octane are used as analytes. The response time, reversibility, hydrophilicity, sensitivity and selectivity of the polymer layers are discussed. According to the results, highly sensitive sensors for each of the analytes are proposed. Based on the characterization method, a convenient and flexible way to the construction of electric nose system by the polymer-coated resonant microcantilevers can be achieved.

Influence of temperature on mass transfer in an incomplete trapping supported liquid membrane extraction of triazole fungicides

The influence of temperature in a supported liquid membrane (SLM) extraction of triazole fungicides was investigated. The mass transfer parameters such as diffusion coefficient, flux and apparent viscosity were determined at temperatures ranging from 5 to 40 degrees C. Increase in temperature led to an increase in diffusion coefficient and flux with a flowing acceptor solution. The apparent viscosity also decreased with an increase in temperature. However, the increase in mass transfer parameters did not result in an overall increase in extraction efficiency with a stagnant or circulation acceptor phase. Stripping of the analytes from the membrane into the acceptor phase as well as the configuration of the extraction unit could have limited the influence of temperature on mass transfer. The partition coefficient of analytes from the acceptor solution to the membrane, K(A), was found to be much higher than that from the donor solution to the membrane K(D), thus triazole compounds preferred to remain in the membrane even with an increased extraction temperature.

An interior needle electropolymerized pyrrole-based coating for headspace solid-phase dynamic extraction

A headspace solid-phase dynamic extraction (HS-SPDE) technique was developed by the use of polypyrrole (PPy) sorbent, electropolymerized inside the surface of a needle, as a possible alternative to solid-phase microextraction (SPME). Thermal desorption was subsequently, employed to transfer the extracted analytes into the injection port of a gas chromatography–mass spectrometry (GC–MS). The PPy sorbent including polypyrrole-dodecyl sulfate (PPy-DS) was deposited on the interior surface of a stainless steel needle from the corresponding aqueous electrolyte by applying a constant deposition potential. The homogeneity and the porous surface structure of the coating were examined using the scanning electron microscopy (SEM). The developed method was applied to the trace level extraction of some polycyclic aromatic hydrocarbons (PAHs) from aqueous sample. In order to enhance the extraction efficiency and increase the partition coefficient of analytes, the stainless steel needle was cooled at 5 °C, while the sample solution was kept at 80 °C. Optimization of influential experimental conditions including the voltage of power supply, the time of PPy electrodeposition, the extraction temperature, the ionic strength and the extraction time were also investigated. The detection limits of the method under optimized conditions were in the range of 0.002–0.01 ng mL −1. The relative standard deviations (R.S.D.) at a concentration level of 0.1 ng mL −1 were obtained between 7.54 and 11.4% ( n = 6). The calibration curves of PAHs showed linearity in the range of 0.01–10 ng mL −1. The proposed method was successfully applied to the extraction of some selected PAHs from real-life water samples and the relative recoveries were higher than 90% for all the analytes.

Influence of temperature on mass transfer in an incomplete trapping single hollow fibre supported liquid membrane extraction of triazole fungicides

The influence of temperature in a single hollow fibre supported liquid membrane extraction of triazole fungicides with a stagnant acceptor phase was investigated. The mass transfer parameters such as diffusion coefficient, flux and apparent viscosity were determined at temperature ranging from 278 K to 313 K. Increase in temperature led to an increase in diffusion coefficient and flux. The apparent viscosity also decreased with an increase in temperature. The degree of trapping in the acceptor phase influenced the mass transfer at higher temperature. At lower temperature, the transport of analytes from the donor solution through the donor–membrane interface and through the membrane mainly affected the transport of triazole fungicides. The effect of temperature in a single hollow fibre SLM extraction technique is therefore more pronounced where transport is donor controlled and/or membrane controlled. The partition coefficient of analytes from the acceptor solution to the membrane, K A was found to be much higher than that of from the donor solution to the membrane K D, thus least trapped triazole fungicides preferred to remain in the membrane even with an increased extraction temperature.

Modeling analyte permeation in cylindrical hollow fiber membrane introduction mass spectrometry

The time-resolved signal generated from membrane introduction mass spectrometry (MIMS) has been modeled in cylindrical coordinates to analyze the data from MIMS experiments, in which a capillary hollow fiber selectively passes a low molar mass analyte dissolved in an aqueous solution to a mass spectrometer. Two approximate solutions are developed to Fick's second law for a step change in upstream concentration. The first, found by a finite Fourier transform, gives an accurate description of the MIMS signal at relatively long times while the second, found via Laplace transform, gives an accurate description at short times. Together with the steady-state solution, the results allow straightforward determination from data of the analyte's diffusivity in the membrane as well as the analyte partition coefficient between the upstream solution and the membrane. Analysis of data for trace levels of toluene in aqueous solution passed through a polydimethylsiloxane (PDMS) hollow fiber yields the diffusion coefficient, partition coefficient, and their temperature dependences for the toluene/PDMS system.

Headspace Sorptive Extraction (HSSE) in the Headspace Analysis of Aromatic and Medicinal Plants

A new sampling technique, Headspace Sorptive Extraction (HSSE), is here applied for the first time to the headspace sampling of medicinal and aromatic plants. The analyte partition coefficient between HSSE-PDMS stir bar and sample headspace (K1), the concentration factor (CF), the reproducibility, and the minimum recoverable amount were determined by analyzing standard solution of high volatility C5–C7 compounds with different polarities and structures (cyclohexane, propyl acetate, hexanal, 1-hexen-3-ol, isoamyl acetate, and 2-heptanol). Four aromatic and medicinal plants, viz. rosemary (Rosmarinus officinalis L.), sage (Salvia officinalis L.), thyme (Thymus vulgaris L.), and valerian (Valeriana officinalis L.) were analyzed by HSSE-GC with PDMS stir bars, and their concentration capacity was compared with those of S-HS and HS-SPME with different fibers. HSSE showed very high concentration capability with both standard and real sample components.

Capillary zone electrophoretic separation of neutral species of chloro- s-triazines in the presence of cationic surfactant monomers

Chloro- s-triazines are difficult to separate by capillary zone electrophoresis (CZE), due to their low p K a values. However, these analytes can be effectively separated by CZE in the presence of cationic surfactant monomers, such as tetradecylammonium bromide (TTAB) and dodecyltrimethylammonium bromide (DTAB). The separation mechanism based on a 1:1 binding of analytes to cationic surfactant monomers is proposed. The binding constants of chloro- s-triazines to cationic surfactant monomers are estimated. The results show that the strength of the interactions of these analytes with TTAB monomers is considerably strong, whereas that of the corresponding analyte with DTAB monomers is about 12- to 14-fold weaker. A linear correlation of binding constants with log P ow (the logarithm of the partition coefficient of analytes between 1-octanol and aqueous phases) indicates that the migration order of these chloro- s-triazines depends primarily on their hydrophobicity. Moreover, the skewed peaks of chloro- s-triazines observed may reveal the occurrence of adsolubilization of these analytes in the adsorbed cationic surfactant layer on the capillary surface.

The sorption of 2-methylnaphthalene by Rossburg Soil in the absence and presence of a nonionic surfactant

The sorption of 2-methylnaphthalene by Rossburg Soil was measured in the absence and presence of a nonionic surfactant (Triton® X-100). Sorption of the surfactant by the sorbent was significant and can be adequately described by the Langmuir isotherm equation. At surfactant equilibrium concentrations below the critical micelle concentration (CMC), sorption of the analyte was enhanced by as much as a factor of 2. At high surfactant dosages, the formation of micelles enhanced the aqueous-phase concentration of the sorbate thereby decreasing its sorption by the soil. A reduction in the analyte partition coefficient by as much as a factor of 3 was observed at a surfactant dosage of 3000 mg/L. A simple three-phase model was used to estimate the effects of surfactants on the sorption of nonpolar organic compounds. This model also took into account the effect of the surfactant on sorbent properties. The model results suggest that very hydrophobic substances ( K ow > 10 5.0) were most sensitive to the effects of the surfactant with regard to enhanced sorption below the equilibrium CMC and increases in solution-phase concentration above the CMC. Moreover, it appears that lower relative surfactant dosages above the CMC are required to effectively mobilize these types of pollutants.

Quantitative Extraction Using an Internally Cooled Solid Phase Microextraction Device

Solid phase microextraction (SPME) is a new extraction technique which uses a fused silica fiber coated with polymeric coating to extract organic compounds from their matrix and directly tranfer analytes into a gas chromatograph (GC) by thermal desorption in a GC injector. SPME has been proven to be simple, time efficient, and sensitive. By sampling from the headspace above sample matrices, SPME can be used to extract target analytes from very complex matrices such as sludge, wastewater, and soil. In this paper, we develop a new approach for headspace SPME sampling. By heating the sample matrix while simultaneously cooling the fiber coating, we not only facilitate the mass transfer and the release of analytes into the headspace but also create a temperature gap between the cold fiber coating and the hot headspace which significantly increases the partition coefficients of analytes

Factors affecting selectivity in micelle exclusion chromatography of inorganic anions

Selectivity in micelle exclusion chromatography is influenced by a number of factor, such as adsorption ability of stationary phases, mobile phase additives, pH of mobile phases and the charge density of micelles. These effects on the retention behaviour of inorganic anions are discussed on the basis of a model that permits the determination of partition coefficient of analytes. If needed, the acid—base equilibrium of an analyte can be involved in the model. A derived equation allows the evaluation of the individual contributions of the neutral and the ionic species to the total partition and the determination of the dissociation constant of the analyte in micellar solution. Stationary phases of low adsorption ability offer unique selectivity and precise partition coefficients.