Micelle formation for improvement of continuous subcritical water extraction of polycyclic aromatic hydrocarbons in soil prior to high-performance liquid chromatography-fluorescence detection

A Review: Subcritical Water Extraction of Organic Pollutants from Environmental Matrices

Most organic pollutants are serious environmental concerns globally due to their resistance to biological, chemical, and photolytic degradation. The vast array of uses of organic compounds in daily life causes a massive annual release of these substances into the air, water, and soil. Typical examples of these substances include pesticides, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs). Since they are persistent and hazardous in the environment, as well as bio-accumulative, sensitive and efficient extraction and detection techniques are required to estimate the level of pollution and assess the ecological consequences. A wide variety of extraction methods, including pressurized liquid extraction, microwave-assisted extraction, supercritical fluid extraction, and subcritical water extraction, have been recently used for the extraction of organic pollutants from the environment. However, subcritical water has proven to be the most effective approach for the extraction of a wide range of organic pollutants from the environment. In this review article, we provide a brief overview of the subcritical water extraction technique and its application to the extraction of PAHs, PCBs, pesticides, pharmaceuticals, and others form environmental matrices. Furthermore, we briefly discuss the influence of key extraction parameters, such as extraction time, pressure, and temperature, on extraction efficiency and recovery.

Rubber industry

Following chapter presents short introductory description of rubber and rubber industry. The main problem of rubber industry is the way of the usage of spent tires. Furthermore very important group of problems arise considering the metal and nonmetal additives which are significant component of the vulcanized rubber. The key attention is dedicated to typical ways of rubber usage in utilization and recovery of metals from spent rubber materials concentrating specifically on used tires processing. The method of recovery of rare metals from rubber tires was described. The rubber debris finds widest use in the field of waste metal solutions processing. The environmental pollution caused by metals poses serious threat to humans. Several applications of the use of waste rubber debris to remove metals from environmental waters were described. Moreover, the agriculture usage of waste tire rubber debris is described, presenting systems where the rubber material can be useful as a soil replacement.

Extraction and separation of carbohydrates and phenolic compounds in flax shives with pH-controlled pressurized low polarity water

A bench-scale pressurized low polarity water (PLPW) extractor was used for the extraction and separation of hemicellulose, cellulose, lignin, and other phenolic compounds in flax shives. In the first part of this research, the key PLPW extraction process variables of temperature, pH, and flow rate, were optimized using central composite design (CCD). Temperature and pH of water had a significant affect on the fractionation of carbohydrates (cellulose and hemicellulose), lignin, and other phenolics. The optimal extraction conditions for the separation of hemicellulose and lignin, determined by the optimization using CCD, were 170 degrees C, pH 3.0, and a flow rate of 2.5 mL/min. Under these extraction conditions, 39.3% of the initial biomass or feed, 70.1% of the hemicellulose, 35.3% of the lignin, and 5.3% of the cellulose were extracted from the flax shives. In order to improve the purity and yield of the cellulose, a two-stage PLPW extraction was examined. The first stage was designed to remove hemicellulose by water at 170 degrees C and the second stage was intended for delignification by a pH 12 buffer at 220 degrees C. The two-stage PLPW extraction effectively removed 63.2% of the feed, 97.3% of hemicellulose, and 86.3% of lignin, while solubilizing 23.9% of cellulose; resulting in a solid residue containing 0.7 g of hemicellulose, 3.5 g of lignin, and 27.3 g of cellulose/100 g of DFS. The PLPW extraction is able to extract and separate components in flax shives by changing pH and temperature. The best case occurs between pH 9.5 and 12, resulting in maximum solubilization of hemicellulose and lignin.

Static-dynamic superheated liquid extraction of hydroxytyrosol and other biophenols from alperujo (a semisolid residue of the olive oil industry)

Hydroxytyrosol and other olive biophenols (OBPs) such as tyrosol, verbascoside, apigenin-7-glucoside, and alpha-taxifolin have been extracted from alperujo by using static-dynamic superheated liquids. Multivariate methodology has been used to carry out a detailed optimization of the extraction. Under the optimal working conditions no further extraction of the target analytes was achieved after 27 min (up to 2800 and 1500 mg/kg of hydroxytyrosol and tyrosol, respectively), so complete removal of them within this interval was assumed. The extract was injected into a chromatograph-photodiode array detector assembly for individual separation-quantification. The efficacy of ethanol/water mixtures to extract OBPs from alperujo has been demonstrated and compared with that of a conventional stirring-based method. These less toxic extractant mixtures are of interest with a view to future human uses of OBPs.

Evaluation of surfactant assisted pressurized liquid extraction for the determination of glycyrrhizin and ephedrine in medicinal plants

Surfactant assisted pressurized liquid extraction (PLE) with a laboratory made system was applied for the extraction of glycyrrhizin in radix glycyrrhizae/liquorice and ephedrine in Ephedra sinica. The proposed system set-up for this current work was simpler as no heating and back pressure regulator was required. Extraction with surfactant assisted PLE was carried out dynamically at a flow of 1.5 mL min(-1), at room temperature, under an applied pressure of 10-20 bar with an extraction time of 45-50 min. The extraction efficiencies of the proposed method using surfactants such as sodium dodecyl sulfate (SDS) and Triton X-100 were compared with sonication using organic solvent for different batches of medicinal plants materials. For the determination of glycyrrhizin in R. glycyrrhizae, the extraction efficiencies of surfactant assisted PLE with SDS and Triton X-100 was observed to be comparable with sonication. The method precision was found to vary from 1.6 to 2.6% (R.S.D., n=6) on different days. For ephedrine in E. sinica, surfactant assisted PLE with SDS was found to give higher extraction efficiencies compared to Triton X-100. The overall method precision for surfactant assisted PLE with SDS for ephedrine in E. sinica was found to vary from 1.5 to 4.1% (R.S.D., n=6) on different days. The marker compounds present in the various medicinal plant extracts were determined by gradient elution HPLC. Our data showed the possibility of PLE at room temperature and the advantages of eliminating the use of organic solvents in the extraction process.

Superheated liquid extraction of oleuropein and related biophenols from olive leaves

Oleuropein and other healthy olive biophenols (OBPs) such as verbacoside, apigenin-7-glucoside and luteolin-7-glucoside have been extracted from olive leaves by using superheated liquids and a static-dynamic approach. Multivariate methodology has been used to carry out a detailed optimisation of the extraction. Under the optimal working conditions, complete removal without degradation of the target analytes was achieved in 13 min. The extract was injected into a chromatograph-photodiode array detector assembly for individual separation-quantification. The proposed approach - which provides more concentrated extracts than previous alternatives - is very useful to study matrix-extractant analytes partition. In addition, the efficacy of superheated liquids to extract OBPs, the simplicity of the experimental setup, its easy automation and low acquisition and maintenance costs make the industrial implementation of the proposed method advisable.

Optimization of extraction of phenolic compounds from flax shives by pressurized low-polarity water

Pressurized low-polarity water (PLPW) extraction of phenolic compounds from flax shive was investigated using statistically based optimization and the "one-factor-at-a-time" method. Extraction variables examined using central composite design (CCD) included temperature, flow rate, and NaOH concentration of the extracting water. Extraction of phenolic compounds including p-hydroxybenzaldehyde, vanillic acid, syringic acid, vanillin, acetovanillone, and feruric acid was affected by temperature and NaOH concentration; and extraction of all phenolic compounds, except ferulic acid, increased with temperature and NaOH concentration of the extracting water. Flow rate had little effect on concentration of phenolic compounds at equilibrium, but the extraction rate at the early phase was higher for higher flow rates. The mechanism of PLPW extraction of flax shive phenolics was also investigated using a two-site kinetic model and a thermodynamic model. To determine the extraction mechanism, flow rate was varied from 0.3 to 4.0 mL/min while temperature and NaOH concentration were fixed at 180 degrees C and 0.47 M, respectively. The flow rate tests showed the extraction rates of total phenolic (TP) compounds increased with flow rate and can be described by a thermodynamic model. The results from the thermodynamic model demonstrated that a K(D) value of 30 agreed with the experimental data in the flow rate range of 0.3-4.0 mL/min. When the effect of the three independent variables was evaluated simultaneously using CCD, a maximum TP concentration of 5.8 g/kg of dry flax shive (DFS) was predicted from the combination of a high temperature (230.5 degrees C), a high initial concentration of NaOH (0.63 M), and a low flow rate (0.7 mL/min). Maximum TP concentration of 5.7 g/kg of DFS was obtained from extraction conditions of 180 degrees C, 0.3 or 0.5 mL/min, and 0.47 M NaOH at equilibrium. A second-order regression model generated by CCD predicted a maximum TP concentration of 5.8 g/kg of DFS under the same extraction conditions, which is well matched with the results from experimental data.

Environmental analysis based on luminescence in organized supramolecular systems

The use of organized supramolecular systems-including micellar media and cyclodextrin inclusion complexes-combined with luminescence techniques in the study and determination of compounds and elements of environmental interest from 1990 to 2005 is reviewed. Analyses of environmental samples performed using fluorescence, photochemically induced fluorescence and phosphorescence spectroscopy as well as liquid chromatography, capillary electrophoresis and flow injection with luminescence detection in the presence of these organized media are described in detail.

Pressurized hot water extraction of bioactive or marker compounds in botanicals and medicinal plant materials

To reduce the use of organic solvent, pressurized hot water extraction (PHWE) has been shown to be a feasible option for the extraction of bioactive and marker compounds in botanicals and medicinal plants. The parameters that may affect the extraction efficiencies in PHWE include temperature, extraction time and addition of small percentage of organic solvent or surfactants. Currently, applications of PHWE for the extraction of thermally labile compounds in botanicals are still rather limited. PHWE with and without the additional of a small percentage of organic solvent such as ethanol is highly suited for the chemical standardization and quality control of medicinal plants. At the same time, it can be applied at the pilot scale as a manufacturing process for medicinal plants. Surfactant assisted PHWE was found to enhance the extraction of thermally labile and more hydrophobic species in medicinal plants at a lower temperature. The addition of small amount of surfactants in PHWE is highly suited for the determination of bioactive or marker compounds in medicinal plants. With proper optimization, PHWE was observed to have good extraction efficiency and precision when compared to other reference methods of extraction.

Pressurized hot water extraction of insecticides from process dust - Comparison with supercritical fluid extraction

Pressurized hot liquid water and steam were used to investigate the possibilities of extracting insecticides (carbofuran, carbosulfan, and imidacloprid) from contaminated process dust remaining from seed-pellet production. Extraction temperature was the most important parameter in influencing the extraction efficiency and rate of extraction, while varying the pressure had no profound effect. A clean-up procedure of the water extracts using solid phase extraction (SPE) was found to be necessary prior to final analysis by high-performance liquid chromatography (HPLC). Quantitative extraction (compared to a validated organic solvent extraction method) of imidacloprid was obtained at temperatures of 100-150 degrees C within 30 min extraction time. Temperatures above 150 degrees C were required to extract carbofuran efficiently. The most non-polar analyte of the investigated compounds, carbosulfan, gave no detectable concentrations with pressurized hot water extraction (PHWE). One reason might be its low solubility in water, and when attempts are made to increase its solubility by increasing the temperature it may degrade to carbofuran. This can explain recovery values above 100% for carbofuran at higher temperatures. A comparison of the PHWE results and those obtained with supercritical fluid extraction (SFE) revealed that PHWE is advantageous for polar compounds, where the solubility of the analyte in water is high enough that lower temperatures can be used. For non-polar compounds carbon dioxide based extraction is preferred unless the target analyte is highly thermostable.

Determination of 3-nitrobenzanthrone in surface soil by normal-phase high-performance liquid chromatography with fluorescence detection

A sensitive method for determining 3-nitrobenzanthrone in surface soil was developed. 3-Nitrobenzanthrone was reduced to 3-aminobenzanthrone by refluxing at 60 degrees C with hydrazine and Raney nickel for 20 min, and 3-aminobenzanthrone was determined by normal-phase high-performance liquid chromatography (HPLC) with fluorescence detection. We used a cyanopropyl stationary phase and an n-hexane-ethyl acetate (3:1, v/v) mobile phase, since 3-aminobenzanthrone exhibits fluorescence in a low-polarity solvent such as n-hexane or ethyl acetate, but not in a polar solvent such as water or methanol. The calibration graph showed good linearity (r2>0.9999) in the range of 0.002-2 ng, and the detection limit was 0.002 ng (S/N=3). 3-Nitrobenzanthrone in extracts from surface soil collected in the Chubu area (central area) of Japan was determined after clean-up using silica gel chromatography and high-performance liquid chromatography on a pyrenylethyl stationary phase. The concentration of 3-nitrobenzanthrone in surface soil was determined in the range of 1.2-1020 pg/g soil.

Static extraction with modified pressurized liquid and on-line fluorescence monitoring. Independent matrix approach for the removal of polycyclic aromatic hydrocarbons from environmental solid samples

The coupling of a static pressurized liquid extractor to a flow injection manifold has allowed real-time on-line fluorescence monitoring of the polycyclic aromatic hydrocarbons (PAHs) extracted from environmental solid samples, which can be used for either screening or semiquantitative purposes. Sodium dodecyl sulfate (SDS) was added to the water for favoring the extraction of the low-polar analytes. Different solid samples such as sandy soil, river sediments, trout and sardine spiked with the target PAHs were subjected to several 15-min static extraction cycles with SDS-water, at 200 degrees C. The results obtained demonstrated that fluorometric monitoring of static pressurized liquid extraction constitutes an approach as efficient as conventional Soxhlet for the extraction of PAHs from solid samples but with the following positive features: (a) drastic reduction of the extraction time as the extraction kinetics can be monitored and thus the end of the leaching step determined independently of the sample matrix; (b) use of water as extractant thus given place to an environmentally friendly method; and (c) coupling of static extraction to subsequent dynamic steps. The method has been applied to a certified reference material (CRM 524, BCR, industrial soil/organics) for quality assurance/validation. The total content of each analyte was determined by HPLC-fluorimetric detection.

Extractions with superheated water

As the temperature of liquid water is raised under pressure, between 100 and 374 degrees C, the polarity decreases markedly and it can be used as an extraction solvent for a wide range of analytes. Most interest has been in its application for the determination of PAHs, PCBs, and pesticides from environmental samples, where it gives comparable results to Soxhlet extraction but more rapidly and without the use of significant volumes of organic solvents. Unlike SPE, n-alkanes are not extracted unless the pressure is reduced and steam is used. Other applications have included the extraction of essential oils from plant material where it preferentially extracts the economically more important oxygenated components compared to steam distillation. The aqueous extract has been concentrated in a number of different methods (solvent extraction, SPE, SPME, extraction disc) or the extraction can be linked on-line to LC or GC. In many cases the superheated water extraction is cleaner, faster and cheaper than the conventional extraction methods.

Application of supercritical and subcritical fluids for the extraction of hazardous materials from soil

Subcritical and supercritical extractions are novel, non destructive techniques which can be applied for the removal of hazardous compounds from contaminated soil without any changes of the soil composition and structure. The aim of the presented review paper is to give information on up-to day results of this method commonly applied by several institutions worldwide. Interest in the application of SC CO2 has been more expressed in the last two decades, which may be related to its favorable characteristics (non-toxic, non-flammable, increase diffusion into small pores, low viscosity under SC conditions, low price and others). However, interest in wet oxidation (WO) and especially in SCWO (the application of water under supercritical conditions with air) has also increased in the last few years. Interest in H2O as a SC fluid, as well as in extraction with water under subcritical conditions may also be related to specific characteristics and the enhanced rate of extraction. Moreover, the solubility of some specific compounds present in soil can be easily changed by adjusting the pressure and temperature of extraction. The high price of the units designed to operate safely at a pressure and temperature much higher than the a critical one of the applied fluids is the main reason why, at present, there is no more broader application of such techniques for the removal hazardous materials from contaminated soil. In the present paper, among many literature citations and their overall review, some specific details related to the development of specific analytical methods under SC conditions are also considered.

A novel cloud-point extraction process for preconcentrating selected polycyclic aromatic hydrocarbons in aqueous solution

A novel but simple cloud-point extraction (CPE) process is developed to preconcentrate the trace of selected polycyclic aromatic hydrocarbons (PAHs) with the use of the readily biodegradable nonionic surfactant Tergitol 15-S-7 as extractant. The concentrations of PAHs, mixtures of naphthalene and phenanthrene as well as pyrene, in the spiked samples were determined with the new CPE process at ambient temperature (23 degrees C) followed by high performance liquid chromatography(HPLC) with fluorescence detection. More than 80% of phenanthrene and pyrene, respectively, and 96% of naphthalene initially present in the aqueous solutions with concentrations near or below their aqueous solubilities were recovered using this new CPE process. Importantly Tergitol 15-S-7 does not give any fluorometric signal to interfere with fluorescence detection of PAHs in the UV range. No special washing step is, thus, required to remove surfactant before HPLC analyses. Different experimental conditions were studied. The optimum conditions for the preconcentration and determination of these selected PAHs at ambient temperature have been established as the following: (1) 3 wt% surfactant; (2) addition of 0.5 M Na2SO4; (3) 10 min for equilibration time; and (4) 3000 rpm for centrifugal speed with duration of 10 min.