Rapid Estimation of Octanol–Water Partition Coefficient for Triazole Fungicides by MEKC with Sodium Deoxycholate as Surfactant

A rapid estimation of octanol–water partition coefficient (log P _ow) was developed for triazole fungicides by micellar electrokinetic chromatography (MEKC). Five standard compounds with known log P _ow values from 2.9 to 4.3 (cyproconazole, bromuconazole, epoxiconazole, bitertanol and difenoconazole) were used for constructing the calibration curve of the log P _ow against the MEKC retention factor, log k. A linear relationship was achieved between log P _ow and log k, in the MEKC system containing 40 mM sodium deoxycholate (SDC) and 4 mM borate buffer at pH 9.3, with a correlation of determination, r ² = 0.9905. The log P _ow values of four test compounds of triazole fungicides (triadimenol, myclobutanil, propiconazole and penconazole) were calculated based on the log k values measured by MEKC and the slope and intercept of the calibration curve. This MEKC method can give good estimation of the log P _ow of the four test compounds of triazole fungicides with the differences between the literature log P _ow values and estimated log P _ow from the MEKC method were from 0.15 to 0.23 log units.     

Assessment of Centrifugal Partition Chromatography for Determination of Octanol-Water Partition Coefficients

Abstract

Centrifugal partition chromatography (CPC) has been assessed as a convenient automated method for the determination of octanol-water partition coefficients (K_OW) over the range of -0.5 to 2.5 log units. The stationary (V_s) and mobile phase (V_m) volumes, which are needed for the calculation of K_ow, are determined in situ by injecting four compounds with known K_ow. V3 and V_m were also determined by independent analytical means to demonstrate that this is a direct measurement of K_ow from fundamental chromatographic principles with no unexplained fitted parameters. Propagation of error shows that a single four-component calibration with duplicate injections of each unknown is sufficient to determine log K_ow with a precision of less than 0.1 log units.     

Water solubility and octanol/water-partitioning of hydrophobic chlorinated organic substances determined by using SPME/GC

The critical step in the determination of water solubilitiy (S _w) and octanol-water partition coefficient (K _ow) of hydrophobic organic chemicals by using the generator-column technique and the slow-stirring procedure, respectively, is the exact quantification of the low water-phase concentrations of the substances under investigation. We have tested the applicability of solid-phase microextraction (SPME) and gas chromatography with seven chlorinated organic compounds. The substances cover a S _w range from 500 mg/L to 7 ng/L and a log K _ow range from 3 to 8. The results show that SPME can be a valuable alternative to common preconcentration techniques in the quantification of hydrophobic organics in pure and octanol-saturated water. The apparent SPME distribution constants K _SPME (obtained with the 100 μm-PDMS fiber for analyte’s partitioning between fiber coating and aqueous sample) do not correlate directly with octanol/water partition coefficients and thus cannot be recommended as a surrogate parameter for K _ow.     

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

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

Nonlinear Dependence of Bioconcentration Factors on n-Octanol-Water Partition Coefficients of Chlorinated Dibenzofurans and Dibenzo-p-Dioxins

Abstract

A nonlinear thermodynamic model is applied to the prediction of both the bioconcentration factor (K_bw) in the guppy (Poecilia reticulata) and the n-octanol-water partition coefficient (K_ow) of chlorinated dibenzofurans and dibenzo-p-dioxins. To this end molar liquid volumes, heats of vaporization and empirically fitted parameters of the pertinent solute and solvents are used. Calculated log K_bw and log K_ow values are obtained with correlation coefficients (r = 0.85 and 0.992) and mean deviations (< dev > = 0.19 and 0.17), which compare favourably with experimental data.

In addition the model enables an explanation of the well-known nonlinear log-log relationship between the two properties for compounds with high K_ow values on the basis of differences between the properties of biotic lipid and n-octanol. It is suggested that the breakdown of the linear relationship is caused by entropic effects related to the number of chlorine atoms in the solute molecules and to the structures of the lipid and n-octanol.     

Dependence of the distribution constant in liquid–liquid partition equilibria on the van der Waals molecular surface area

The direct calculation of free energy of interactions between a solute j and two immiscible liquids shows a linear dependence between the (logarithm of) the distribution constant in liquid–liquid partition equilibrium log K_j and the van der Waals surface area of the solute. The study provides a thermodynamic proof for the formula log K_BA,j = c₁ log K_BC,j + c₂ that describes the linear dependence between (the logarithm of) the distribution constant for a solute j in a solvent system (B/A) and (the logarithm of) the distribution constant for the same solute in a different solvent system (B/C). This relation has been well proven by various experimental studies and it is frequently used in liquid chromatographic separations as well as in liquid–liquid extractions, but was not explained previously based on thermodynamic results. The theory was verified using the prediction of octanol/water distribution constants log K_ow for a wide range of molecules, including hydrocarbons and compounds with a variety of functional groups. The results have also been verified for the distribution constants in other solvent systems. The expression for the distribution constant obtained in this study also gives a theoretical base for the additive fragment methodology used for the prediction of log K_ow.     

Determination of Octanol–Water Partition Coefficients,Water Solubility and Vapour Pressures of Alkyl-lead Compounds

Physico-chemical properties of alkyl-lead compounds, namely aqueous solubility, octanol–water partition coefficient ( K _ow), vapour pressure and Henry's Law constant, have been determined. Vapour pressures of trialkyl-lead salts at different temperatures were measured by a gas-saturation technique in which air was passed slowly through a glass column packed with pure solid alkyl-lead compounds. K _ow of tetra-alkyl-lead (TAL) and trialkyl-lead (TriAL) were determined under different salinity and pH conditions, and the latter were related to the species (R₃Pb⁺, R₃PbOH⁰ or R₃PbCl⁰) dominating under a particular set of conditions. Regression calculations incorporating melting point corrections relate water solubility to K _ow, and provide a means of estimating either parameter for a wider range of compounds.     

Evaluation of low-cost disposable polymeric materials for sorptive extraction of organic pollutants in water samples

The capabilities of four commercially available and low cost polymeric materials for the extraction of polar and non-polar contaminants (log K_ow = −0.07–6.88, from caffeine to octocrylene, respectively) from water samples was compared. Tested sorbents were polyethersulphone, polypropylene and Kevlar, compared to polydimethylsiloxane as reference material. Parameters that affect the extraction process such as pH and ionic strength of the sample, extraction time and desorption conditions were thoroughly investigated. A set of experimental partition coefficients (K_pw), at two different experimental conditions, was estimated for the best suited materials and compared with the theoretical octanol–water (K_ow) partition coefficients of the analytes. Polyethersulphone displayed the largest extraction yields for both polar and non-polar analytes, with higher K_pw and lower matrix effects than polydimethylsiloxane and polypropylene. Thus, a sorptive microextraction method, followed by large volume injection (LVI) gas chromatography–tandem mass spectrometry (GC–MS/MS), was proposed using the former sorbent (2 mg) for the simultaneous determination of model compounds in water samples. Good linearity (>0.99) was obtained for most of the analytes, except in the case of 4-nonylphenol (0.9466). Precision (n = 4) at 50 and 500 ng L⁻¹ levels was in the 2–24% and limits of detection (LODs) were in the 0.6–25 ng L⁻¹ range for all the analytes studied.     

Validation of pH-Metric Technique for Measurement of pKa and log Pow of Ionizable Herbicides

Abstract

Knowing the values of pK_a and partition coefficients between 1-octanol and water (P_ow) of ionizable herbicides helps us to understand the movement of these compounds in plants and soil. However, shake-flask and high-pressure liquid chromatography (HPLC) techniques. though valuable for measurement of log P_ow of herbicide molecules that do not ionize in aqueous solution, are difficult to use for ionizable molecules; this is especially so for molecules that form ion pairs having appreciable log P_ow values, those with multiple ionizations and for bases with high pK_a values. Our aim in this study was to validate the use of the pH-metric technique (based on potentiometric titration) for measurements of pK_a and log P_ow of ionizable standard substances and herbicides. The values obtained show good correlation with results from other techniques, including shake-flask and HPLC. The OECD Guideline for Testing of Chemicals 117, adopted 30th March 1989, describes the use of HPLC for the measurement of log P_ow. It is hoped that these studies and further testing of this technique will permit it to be included in these OECD guidelines.     

Quantitative Relationships of Structure-Activity and Volume Fraction For Selected Nonpolar and Polar Narcotic Chemicals

Abstract

The relative toxicity of selected industrial organic chemicals was secured from the literature for the static 48-h Tetrahymena pyriformis 50% population growth impairment and the flow-through 96-h Pimephales promelas 50% mortality endpoints. Chemicals were selected to represent the nonpolar narcosis (aliphatic alcohols and aliphatic ketones) and polar narcosis (anilines and phenols) mechanisms of toxic action. molar volume (MV) and 1-octanol/water partition coefficient (log K _ow) data were generated for each chemical. High-quality, log K _ow dependent quantitative structure-activity relationships were observed for each chemical class and mechanism of action for both endpoints. The volume fraction (V _t) for each chemical in the target phase was determined from the toxicant concentration in the water (toxicity data), the MV, and the target/water partition coefficient (K _tw) with K _tw considered equal to K _ow ^(1-a). Analyses of target sites, by way of “a” revealed that “a” was constant for a mechanism of action regardless of chemical class, but distinct for a given test system. Mean V _t was constant for each mechanism of action regardless of chemical class or test system. These results suggest, at least for reversible physical mechanisms, that volume fraction analyses are significant in determining the mechanism of toxic action of a chemical.     

Equilibrium and kinetic solid-phase microextraction determination of the partition coefficients between polychlorinated biphenyl congeners and dissolved humic acid

A conventional solid-phase microextraction (SPME) method combined with liquid–liquid extraction was applied under equilibrium and nonequilibrium conditions to determine the partition coefficients (K_doc) of 25 polychlorinated biphenyl congeners (PCBs) between Sigma–Aldrich humic acid (HA) and water. The values of log K_doc determined with equilibrium SPME were linearly correlated with the logarithm of the octanol–water partition coefficients (K_ow) for PCB congeners at log K_ow < ∼7.2, but the trends were disrupted for log K_ow from ∼7.2 to 8.18. In addition, short-term (5 min to 4 days) and long-term (5–44 days) uptake profiles of PCBs were established, from which a pseudo-equilibrium for sorption of PCBs was revealed at ∼4 days of extraction. To understand this phenomenon, the uptake profiles were fitted with two equations (one equation is often used for pure water samples and the other one is applicable for samples containing complex matrices) derived from a first-order kinetics model. Subsequently, K_doc values obtained through kinetic approaches were compared with those acquired from equilibrium SPME. The comparison of K_doc values indicated that the pseudo-equilibrium was caused by the slow desorption of PCBs from HA rather than the biphasic desorption mechanism.     

Predicting 1-octanol-water partition coefficient by high-performance liquid chromatography gradient elution

The method to predict 1-octanol-water partition coefficients (K _ow) from capacity factors (k) obtained by Reversed-Phase High-Performance Liquid Chromatography (RP-HPLC) has been extended to use gradient elution rather than isocratic elution. The mobile phase has been changed either linearly or exponentially with time. The initial composition of the mobile phase and its rate of change affected the log K _ow versus log k relation. This relation was exponential in linear gradient experiments. For non-linear gradient elution in which the water fraction of the mobile phase decreased exponentially from 100% to approach 0% asymptotically, a physically-based equation describing the dependence of log K _ow on log k has been derived. Without any preliminary estimation, RP-HPLC gradient elution allows a precise prediction of log K _ow over a range of nearly six orders of magnitude.     

Phase Ratio and Equilibrium Constant in RP-HPLC Obtained from Octanol/Water Partition Constant Through Solvophobic Theory

The experimentally known dependence in RP-HPLC of the retention factor k′ on octanol/water partition coefficient (K _ow) has been examined based on solvophobic theory. The result showed that the dependence provides a means for the evaluation of phase ratio (Φ) of RP-HPLC columns, and of the equilibrium constant for a given compound and mobile phase. Using this theory, the phase ratio was evaluated for a set of seven different C18 columns (five having fully porous particles and two core–shell particles), and the equilibrium constants were calculated for four homologous series of compounds in two mobile phase systems. One mobile phase was methanol/aqueous solution of 0.1% H₃PO₄, and the other was acetonitrile/aqueous solution of 0.1% H₃PO₄. Besides providing the values for Φ for the evaluated columns, the results of the study indicated that for a specific composition of the mobile phase and for a given compound displaying only hydrophobic interactions, the equilibrium constant K(X) for different C-18 columns is basically the same. The data were further used to provide guidance in the selection of a chromatographic column for a specific separation based on K _ow values and chemical structure of the analytes. The study indicated that the separation of compounds with identical polar groups (or no polar groups) and with very close values for the K _ow cannot be achieved based only on hydrophobic interactions that dominate the separation on RP-type columns. Only column that displays polar interactions may provide a solution to such separations. For hydrocarbons with close K _ow values, the separation cannot be achieved even on columns with some polarity. On the other hand, even compounds with equal K _ow values, but with different functionalities can be separated on RP-HPLC columns without involving polar interactions. The compounds with different K _ow values are expected to be easily separated on RP-HPLC columns.     

Water solubility and octanol/water-partitioning of hydrophobic chlorinated organic substances determined by using SPME/GC

The critical step in the determination of water solubilitiy (S _w) and octanol-water partition coefficient (K _ow) of hydrophobic organic chemicals by using the generator-column technique and the slow-stirring procedure, respectively, is the exact quantification of the low water-phase concentrations of the substances under investigation. We have tested the applicability of solid-phase microextraction (SPME) and gas chromatography with seven chlorinated organic compounds. The substances cover a S _w range from 500 mg/L to 7 ng/L and a log K _ow range from 3 to 8. The results show that SPME can be a valuable alternative to common preconcentration techniques in the quantification of hydrophobic organics in pure and octanol-saturated water. The apparent SPME distribution constants K _SPME (obtained with the 100 μm-PDMS fiber for analyte’s partitioning between fiber coating and aqueous sample) do not correlate directly with octanol/water partition coefficients and thus cannot be recommended as a surrogate parameter for K _ow. Received: 15 January 1997 / Revised: 2 May 1997 / Accepted: 8 May 1997     

Capabilities and limitations of dispersive liquid–liquid microextraction with solidification of floating organic drop for the extraction of organic pollutants from water samples

Dispersive liquid–liquid microextraction with solidification of floating organic drop (DLLME-SFO) is one of the most interesting sample preparation techniques developed in recent years. Although several applications have been reported, the potentiality and limitations of this simple and rapid extraction technique have not been made sufficiently explicit. In this work, the extraction efficiency of DLLME-SFO for pollutants from different chemical families was determined. Studied compounds include: 10 polycyclic aromatic hydrocarbons, 5 pesticides (chlorophenoxy herbicides and DDT), 8 phenols and 6 sulfonamides, thus, covering a large range of polarity and hydrophobicity (Log K_ow 0–7, overall). After optimization of extraction conditions using 1-dodecanol as extractant, the procedure was applied for extraction of each family from 10-mL spiked water samples, only adjusting sample pH as required. Absolute recoveries for pollutants with Log K_ow 3–7 were >70% and recovery values within this group (18 compounds) were independent of structure or hydrophobicity; the precision of recovery was very acceptable (RSD < 12%) and linear behavior was observed in the studied concentration range (r² > 0.995). Extraction recoveries for pollutants with Log K_ow 1.46–2.8 were in the range 13–62%, directly depending on individual Log K_ow values; however, good linearity (r² > 0.993) and precision (RSD < 6.5%) were also demonstrated for these polar solutes, despite recovery level. DLLME-SFO with 1-dodecanol completely failed for extraction of compounds with Log K_ow ≤ 1 (sulfa drugs), other more polar extraction solvents (ionic liquids) should be explored for highly hydrophilic pollutants.     

Determination of the n‐octanol/water partition coefficients of weakly ionizable basic compounds by reversed‐phase high‐performance liquid chromatography with neutral model compounds

A strategy to utilize neutral model compounds for lipophilicity measurement of ionizable basic compounds by reversed‐phase high‐performance liquid chromatography is proposed in this paper. The applicability of the novel protocol was justified by theoretical derivation. Meanwhile, the linear relationships between logarithm of apparent n‐octanol/water partition coefficients (logK_ow′′) and logarithm of retention factors corresponding to the 100% aqueous fraction of mobile phase (logk_w) were established for a basic training set, a neutral training set and a mixed training set of these two. As proved in theory, the good linearity and external validation results indicated that the logK_ow′′–logk_w relationships obtained from a neutral model training set were always reliable regardless of mobile phase pH. Afterwards, the above relationships were adopted to determine the logK_ow of harmaline, a weakly dissociable alkaloid. As far as we know, this is the first report on experimental logK_ow data for harmaline (logK_ow = 2.28 ± 0.08). Introducing neutral compounds into a basic model training set or using neutral model compounds alone is recommended to measure the lipophilicity of weakly ionizable basic compounds especially those with high hydrophobicity for the advantages of more suitable model compound choices and convenient mobile phase pH control.     

Retention prediction and hydrophobicity estimation of weak acidic compounds by reversed-phase liquid chromatography using acetic and perchloric acids as ion suppressors

Simple acids are usually applied to suppress the ionization of weakly ionizable acidic analytes in reversed-phase liquid chromatography. The purpose of this study is to investigate the retention behavior of various weak acidic compounds (monoprotic, diprotic, triprotic, and tetraprotic acids) using acetic or perchloric acid as ion suppressor in a binary hydroorganic mobile phase. The apparent n-octanol–water partition coefficient (K _ow ″) was proposed to calibrate the n-octanol–water partition coefficient (K _ow) of weak acidic compound. LogK _ow ″ was found to have a better linear correlation with logk _w, the logarithm of the retention factor obtained by extrapolating to neat aqueous fraction of the mobile phase, for all weakly ionizable acidic compounds. This straightforward relationship offers a potential medium for direct measurement of K _ow data of weak acidic analytes and can be used to predict retention behavior of these compounds in the ion suppression reversed-phase liquid chromatographic mode.