Modified superheated water extraction of pesticides from spiked sediment and soil

In this study a laboratory-made superheated water system was applied in order to extract some pesticides from sand, sediment and soil samples. Extraction efficiencies were investigated at different time intervals with regard to temperature, type and amount of organic modifier. Pesticides were removed from the aqueous extract using dichloromethane as a trapping solvent. The optimal extraction temperature from sand specimens for malathion, heptachlor, aldrin, dieldrin, butachlor, metalaxyl and propiconazole was found to be 160 °C, while those for chlordane and thiobencarb were 120 °C and 180 °C, respectively. The static extraction time for heptachlor, aldrin, dieldrin, butachlor and metalaxyl was found to be 15 min, whereas for malathion and thiobencarb it was 5 min, and for chlordane and propiconazole it was 10 and 20 min, respectively. Recoveries for the extractions of the pesticides from sand under optimized extraction conditions ranged between 96 and 101%. Those obtained from sediment under such conditions were unsatisfactory, and were consequently improved by adding an organic modifier to the superheated water, and sodium chloride to the extract during liquid-liquid extraction. These procedures were optimized further for the parameters described and recoveries exceeded 91%, with the exception of butachlor. The extraction technique was also applied to soil samples at a reduced water flow rate of 0.5 mL min⁻¹, yielding recoveries of 82–105%, and 76% for dieldrin. The reproducibilities, expressed as relative standard deviations (RSDs), ranged between 2 and 13%.     

Chromatographic determination of the solubility of low soluble substances—A practical possibility

Using selected examples we demonstrate the determination of solubility of low soluble substances with the help of planar chromatography, which is a new, simple and rapid approach to the problem, to a certain extent challenging the established methods. Our approach is a practical consequence of the thermodynamic view of the chromatographic processes, involving either the adsorption or partition mechanism of separation.

---

Chromatographische Bestimmung der Löslichkeit von schwerlöslichen Substanzen — eine praktische Möglichkeit

Zusammenfassung An den gewählten Beispielen wird die Bestimmung der Löslichkeit schwerlöslicher Substanzen mit Hilfe der planaren Dünnschichtchromatographie demonstriert. Dieses Verfahren stellt eine neue, einfache und schnelle Methode dar, die in einem gewissen Maß in Konkurrenz zu den älteren und anerkannten Methoden tritt. Die Methode ist die praktische Konsequenz der thermodynamischen Betrachtung des chromatographischen Prozesses in der Adsorptions- und Verteilungsdünnschichtchromatographie.

     

Demetalization of oils resulting from recycled tires by liquid-liquid extraction using modified superheated water An environmentally friendly approach

An approach based on continuous pressurized liquid-liquid extraction with 20% HNO₃/1 M KCl/10⁻³ M EDTA as extractant has been developed for the extraction of metals from the oil resulting from recycled tires. A multivariate optimization of the main variables affecting the extraction process has been performed. The method has been applied to three oil samples with different contents in V, Ni, Zn, Fe and Cu. The target metals have been determined in both untreated and treated oil by flame atomic absorption spectrometry (FAAS) in order to obtain the extraction efficiency. Under the optimum conditions, recoveries higher than 90% have been obtained with a repeatability and within-laboratory reproducibility, expressed as relative standard deviations, ranging from 2.75 to 6.91 and 2.97 to 8.16%, respectively. For applications where the demetalization does not require being complete, a study of the demetalization degree achieved depending on the extraction temperature and extractant composition has also been performed. This study provides useful data about the cheapest working conditions to be used in order to obtain a given demetalization level.     

Buffered superheated water as an eluent for reversed-phase high performance liquid chromatography

Summary Inorganic buffers have been used to control the pH of a superheated water eluent for reversed-phase liquid chromatography. Using a temperature gradient from 70–190 °C, the relative order of elution of a series of sulfonamides on a polystyrene-divinyl benzene column was determined at pH 3, 7 and 11. The separations were compared with conventional reversed-phase separations on polymer and ODS-bonded silica columns. The apparent pK _a values of selected sulfonamides at elevated temperatures were determined from their retention factors across in a range of superheated buffers and the values were compared to those reported at room temperature.     

Headspace gas chromatographic determination of aromatic hydrocarbons in natural and waste water

Summary The possibilities of using headspace analysis of aromatic hydrocarbon traces in aqueous solutions with changing values of the partition coefficients are discussed. A variant of headspace analysis of the simplest aromatic hydrocarbon in natural and waste water is described. It involves two-step gaseous extraction of a sample in vessels of varying volume before and after the equilibrium phase is replaced with a pure gas (air or nitrogen). This method permits to analyse 5–50 ml water samples with benzene and toluene contents varying from the ppb to the ppm range within an error not exceeding 155. The analysis time is about 1.5 h. The presence of non-volatile organic or mineral substances does not influence the determination. This method is unsuitable to heterogeneous systems (aqueous oil emulsions): before carrying out the analysis for the hydrocarbon content these systems have to be homogenized first.Presented at the Scientific Seminar on Headspace Gas Chromatography organized in cooperation with the Perkin-Elmer Corporation (Norwalk, CO, USA) in Leningrad, December 4–5, 1979.     

Measuring the solubilities of ionic liquids in water using ion-selective electrodes

Polyvinyl chloride-plasticized membrane ion-selective electrodes (ISE) based on conventional ion-exchangers have been proposed as a cheap universal tool to measure the solubilities of ionic liquids (ILs) in water. They are applicable for ILs with a wide range of solubilities in water, since the linear range of a potentiometric response spans several orders of magnitude. As an example, we have fabricated and tested ISEs for widely used alkylimidazolium ionic liquids. The aqueous solubilities of four typical ILs have been determined at 21 °C: 0.075±0.001 mol l^–1 (1-butyl-3-methylimidazolium, BMIm, hexafluorophosphate); 0.018±0.001 mol l^–1 (BMIm bis(triflylimide)); 0.054±0.007 mol l^–1 (1-butyl-2,3-dimethylimidazolium, BDMIm, hexafluorophosphate); 0.014±0.001 mol l^–1 (BDMIm bis(triflylimide)).     

Static and dynamic superheated water extraction of essential oil components from Thymus vulgaris L.

Superheated water extraction (SWE) performed in both static and dynamic condition (S‐SWE and D‐SWE, respectively) was applied for the extraction of essential oil from Thymus vulgaris L. The influence of extraction pressure, temperature, time, and flow rate on the total yield of essential oil and the influence of extraction temperature on the extraction of some chosen components are discussed in the paper. The SWE extracts are related to PLE extracts with n‐hexane and essential oil obtained by steam distillation. The superheated water extraction in dynamic condition seems to be a feasible option for the extraction of essential oil components from T. vulgaris L.     

Simultaneous determination of volatile aromatic and halogenated hydrocarbons in water and soil by dual-channel ECD/PID equilibrium headspace analysis

Volatile aromatic and halogenated hydrocarbons are determined in water and soil samples by equilibrium headspace gas chromatography. Simultaneous analysis is carried out in a dual column/dual detector arrangement with ECD and PID. Their determination in contaminated soil is performed with the same instrumental configuration. However, in contrast to water analysis, an increased sample temperature was found necessary for highly adsorptive soil specimens. At sample temperatures of 95 °C, recoveries near 100% have been found. Both adsorption and desorption processes were found to be strongly time-dependent.     

芳烃化合物结构参数与色谱保留值关系的探讨

在自制的十六烷基磷酸锡固定相、甲醇－水流动相的色谱体系中，建立了烷基取代苯、不同数目的甲基取代苯、稠环芳烃等溶质的色谱保留值与其分子结构参数（分子连接性指数、范德华体积）之间的回归方程，并用疏溶剂理论予以解释，同时探讨了结构参数与色谱热力学的关系。     

Effect of pressure on the solubilities ofo-,m- andp-xylene in water

The solubilities of o-, m- and p-xylene in water were measured at 25.0°C up to 250, 385, and 50 MPa, respectively. The solubility increased with increasing pressure up to 120 MPa (50 MPa for p-xylene) and then decreased. The reaction volumes, V^o accompanying the dissolution at 0.1 MPa were estimated as –3.6±0.5, –3.4±0.5, and –4.1±0.5 cm³-mol^–1 for o-, m-, and p-xylene, respectively, from the pressure dependences of the solubilities. The limiting partial molar volumes, of p- and o-xylene in water under high pressure were estimated from V^o and the molar volume of the xylene. The partial molar volumes decreased with increasing pressure. The reaction volume for the formation of intra-molecular pairwise hydrophobic interaction between the methyl groups, as proposed by Ben-Naim, is discussed for the V^o of p- and o-xylene at 0.1 MPa.     

Green method development approach of superheated water liquid chromatography for separation and trace determination of non-steroidal anti-inflammatory compounds in pharmaceutical and water samples and their extraction

Non-steroidal anti-inflammatory drugs (NSAIDs) are pharmaceutical compounds with anti-inflammatory, analgesic, and antipyretic effects. Herein, a simple and rapid high-temperature liquid chromatography and superheated water chromatography method was developed and validated for the trace determination of NSAID residues of ketoprofen, naproxen, sodium diclofenac, and ibuprofen in water samples. The NSAIDs were separated in less than five minutes using buffered distilled water as the mobile phase and ODS Zirconia RP-C18 column as the stationary phase. Linearity was observed in the van’t Hoff plots of the tested drugs by employing a low acetonitrile percentage (20% ACN) in the mobile phase, without any significant changes in their retention mechanisms. However, nonlinear van’t Hoff plots were obtained for the superheated water chromatography data of the tested drugs because of significant changes in their retention factors, transition stage of the stationary phase, or the mobile phase properties. The limits of detection for ketoprofen, naproxen, sodium diclofenac, and ibuprofen were 14, 2, 4.2, and 32 µg L^?1, respectively, and their limits of quantification were 44, 8, 12, and 98 µg L^?1, respectively. The accuracy and precision parameters were determined for selected drugs, where the relative standard deviations were in the range of ± 0.2179–2.6741%. In addition, these conditions were employed for the removal of NSAIDs from the water samples using carbon nanotubes. The proposed system was applied for the separation and analyses of drugs in water and pharmaceutical samples, and acceptable recoveries of 90.48–98.15% for the water samples and 99.9–100.08% for the pharmaceutical samples were obtained.     

Nonlinear dependence of the solubility of water in hydrocarbons on the molar volume of the hydrocarbon

The solubility of water in fifty hydrocarbon solvents at 20°C is estimated by means of the solubility equation derived from the thermodynamics of mobile order in H-bonded liquids. Neglecting the change in nonspecific cohesion forces, and assuming that water is primarily monomeric in solution, the prediction accounts for two main effects: the breaking of the H-bond network linking the water solute molecules together, and the entropy of exchange between water and solvent molecules in solution. The formation of a weak O–H ... hydrogen bond interaction is moreover taken into account according to whether the hydrocarbon is saturated or not. The overall predictive equation foresees a non-linear dependence of the water solubility on the molar volume of the hydrocarbon. Several rules are presented regarding the water solubility-hydrocarbon structure relationship.     

PDMS extraction bars for the determination of volatile aromatic hydrocarbons in water and wastewater

In this study, the preparation and application of extraction bars of PDMS were investigated to preconcentrate and determine benzene, toluene, ethylbenzene, and xylene in water and wastewater by means of HPLC with fluorescence detection. Aliquot samples from hospital wastewater were used as the model effluent. The independent variables for the sorptive extraction were as follows: ionic strength (added amounts of NaCl); pH; temperature and time of absorption; temperature and time of desorption. Under optimized conditions, by using a factorial design, the suspended extraction bars could allow the determination of benzene, toluene, ethylbenzene, and xylene (1.20 ± 0.05 μg/L; 10.40 ± 0.02 μg/L; 1.80 ± 0.04 μg/L; 15.9 ± 0.04 μg/L, respectively) in hospital effluent (fortified samples), by recoveries of 71.9 ± 4.9 to 74.8 ± 5.6%. This procedure represents an innovation that eliminates the time‐consuming stage of vacuum microfiltration, and allows the determination of volatile organic compounds by HPLC. As far as we know, this procedure is original and represents an important contribution to the field.     

Electrospun polymer nanofibers as a solid-phase extraction sorbent for the determination of trace pollutants in environmental water

This paper describes the novel preparation of three kinds of nanofibers [poly(styrene-co-methacrylic acid), poly(styrene-co-p-styrene sulfonate), polystyrene] investigated as solid-phase extraction (SPE) sorbents to extract six compounds (nitrobenzene, 2-naphthol, benzene, n-butyl p-hydroxybenzoate, naphthalene, p-dichlorobenzene) in environmental water by high-performance liquid chromatography. Parameters affecting extraction efficiency were investigated in detail to explore the extraction mechanism of the nanofibers. Under optimized conditions, six compounds followed an excellent linear relationship in the range 10–5,000 ng mL⁻¹ with coefficients of determination (r ²) greater than 0.99. The repeatability (expressed as relative standard deviations) was from 3.0 to 7.0%, corresponding to 2.0 mL of water samples at 25 and 500 ng mL⁻¹ spiked levels for the six compounds. The limits of detection varied from 0.01 to 0.15 ng mL⁻¹ (signal-to-noise ratio of3). A comparison of the SPE using nanofibers as sorbents and the most commonly used octadecylsilica SPE cartridges was carried out in terms of absolute recovery, sensitivity, and reproducibility for the compounds investigated. Finally, the method was applied to four real water samples. The results highlighted the importance of functional groups, and the polarity of nanofibers in controlling sorption of target compounds, and clearly showed that the new method could be a viable and environmentally friendly technique for analyzing pollutants in environmental samples.     

Chromatographic determination of solubility of low soluble substances the physico-chemical basis

The physico-chemical basis for a direct chromatographic determination of solubility of low soluble substances by means of adsorption and partition TLC is discussed. This method is a practical consequence of the chromatographic binary solutions model, a new semi-empirical approach based on phenomenological thermodynamics.

---

Chromatographische Bestimmung der Löslichkeit von schwerlöslichen Substanzen. Die physikalisch-chemische Basis (Kurze Mitteilung)

Zusammenfassung Die physikalisch-chemische Basis einer direkten chromatographischen Bestimmung der Löslichkeit von schwerlöslichen Substanzen mit Hilfe der Adsorptions- und Verteilungsdünnschichtchromatographie wird diskutiert. Die Möglichkeit einer solchen Bestimmung ist die praktische Konsequenz des chromatographischen Modells der binären Lösungen, einer neuen semiempirischen, auf der phänomenologischen Thermodynamik begründeten Methode.

     

Extraction of fatty acids from grape seed by superheated hexane

Superheated hexane extraction has been tested for obtaining fatty acids from grape seed and compared with conventional Soxhlet and hot hexane extractions. Seeds from grape residues from a winery were dried for 46 h at 105 °C, milled and sieved by particle size (d < 0.42 mm, 0.42 < d < 0.84 mm and d > 0.84 mm). An optimization study of influential variables on superheated hexane extraction (namely extraction time, temperature, pression, particle size and sample amount) was carried out by a multivariate approach. All the extracts were concentrated in a rotary evaporator and dried by adding 1 g of Na₂SO₄. Then, 2 ml of the dried extract were subjected to reaction with 1 ml of a 0.5 M solution of sodium methylate in methanol to obtain fatty acid methyl esters (FAMEs). After derivatization, FAMEs were quantified by GC-FID. The results show that the optimal conditions for superheated hexane extraction are: time extraction, 10 min; temperature, 80 °C; pressure, 40 bar; particle size, d < 0.42 mm; amount of sample, 0.4 g. Under these conditions, around 84% of the fatty acids (out of the amount obtained by Soxhlet extraction) is extracted. Comparison with Soxhlet and hot hexane extractions showed that the percentages of FAMEs are similar in all the extracts and they agree with the data in the bibliography.     

Processing polyamides with superheated water

Superheated water (shH₂O) is investigated as a process aid in conventional aliphatic polyamide (PA) systems. The polymers investigated include PA 6 (PA6), PA 6,6 (PA66), PA 6,12 (PA612), and PA 12 (PA12). It is shown that the PA melting and crystallization temperatures are significantly reduced when exposed to shH₂O. For example, the melting temperature of PA6 is depressed from 206 to 153 °C in the presence of shH₂O. A relationship between amide group density and thermal transition temperature reduction is observed. Processing these materials in shH₂O has led to a variety of materials ranging from low‐density foams to higher density locally anisotropic foamed morphologies. In situ observations of PAs melting in the presence of shH₂O are performed using a specially designed reactor. Results from these experiments are used to estimate the diffusion coefficient of shH₂O in PA6. Finally, low‐temperature extrusion is performed with PA6 and shH₂O at temperatures as low as 180 °C and mixture viscosity is estimated. A 20‐fold depression in the melt viscosity of PA6 is observed at 240 °C with shH₂O. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 803–813     

Single-drop microextraction technique for the determination of antibiotics in environmental water

Growing concerns related to antibiotic residues in environmental water have encouraged the development of rapid, sensitive, and accurate analytical methods. Single-drop microextraction has been recognized as an efficient approach for the isolation and preconcentration of several analytes from a complex sample matrix. Thus, single-drop microextraction techniques are cost-effective and less harmful to the environment, subscribing to green analytical chemistry principles. Herein, an overview and the current advances in single-drop microextraction for the determination of antibiotics in environmental water are presented were included. In particular, two main approaches used to perform single-drop microextraction (direct immersion-single-drop microextraction and headspace-single-drop microextraction) are reviewed. Furthermore, the impressive analytical features and future perspectives of single-drop microextraction are discussed in this review.     

Enhancement of the solubilities of polycyclic aromatic hydrocarbons by weak hydrogen bonds with water

Summary The thermodynamics of mobile order is applied to predict the aqueous solubility of liquid and solid aliphatic and polycyclic aromatic hydrocarbons. The solubility values are mainly determined by the magnitude of the hydrophobic effect. However, contrary to the solubilities of the alkanes, the solubilities of polycyclic aromatic hydrocarbons in water predicted in absence of solute-solvent hydrogen (H) bonds are systematically too low. This shows the contribution of weak specific interactions between the OH groups and the electrons of the aromatic substances. According to the theory, these interactions are characterized by a stability bility constant K_o which can be derived from solubility data. At 25°C, this constant amounts to 80 cm³/mol, the order of magnitude of which can be explained by the competition of these intermolecular bonds with the rather weak self-association bonds in the secondary chains of water.