High thermal-stable sol–gel-coated calix[4]arene fiber for solid-phase microextraction of chlorophenols

Application of boehmite as a fiber coating for headspace solid-phase microextraction of chlorophenols from aqueous samples

In this paper, the extraction of chlorophenols from water samples was carried out using high surface area boehmite nanoparticles as a sorbent. The surfactant-free process employed to make the nano-boehmite used in this work was simple, green, and efficient. The proposed approach was based on headspace solid-phase microextraction, followed by GC-ECD for the determination of analytes. In situ derivatization of analytes was performed with acetic anhydride in a basic medium. Various effective parameters, including the amount of derivatization reagent, ionic strength, desorption temperature and time, extraction temperature, equilibrium time, and extraction time were studied. Under optimal conditions, the linear dynamic range was 0.05-5.0 μg L-1 for 2,4-dichlorophenol and 2,6-dichlorophenol and 0.003-0.1 μg L-1 for 2,4,6-trichlorophenol. A low limit of detection (0.75 × 10-3-15 × 10-3 μg L-1), and relative standard deviations for real samples (RSDs) <10% were obtained. The precision (as intra- and inter-day RSDs) was between 1.2 and 9.8%. In comparison to commercial fibers (CAR-PDMS, 85 μm), this fiber showed a greater extraction efficiency. Various water samples were subjected to extraction by the proposed method. The recoveries ranged from 90 to 110%.

The elimination and extraction of organosulfur compounds from real water and soil samples using metal organic framework/graphene oxide as a novel and efficient nanocomposite

In the present work, an efficient metal organic framework/graphene oxide (MOF-801/GO) sorbent was fabricated and employed for the detection of organosulfur pesticides (OSPs) in real samples using gas chromatography-flame photometric detection (GC-FPD). The optimal extraction parameters for the suggested solid-phase extraction (SPE) include sorbent amount (60 mg), extraction solvent (acetonitrile) and extraction time (5 min). The linear dynamic ranges and detection limits for organosulfur pesticides (OSPs) samples under above extraction conditions were ranged from 0.5 to 300 μg L^-1 and 0.1-1.1 μg L^-1, respectively. Moreover, the proposed SPE/GC-FDP method was applied for the analysis of pesticides in different real environmental water and soil samples. The obtained recoveries of the analytes in were between 92.0 and 106.8% and relative standard deviation (RSD) values were lower than 9.2%. The application of the MOF-801/GO as a sorbent in dSPE of OSPs analytes showed to be reliable, fast and sensible methodology for pesticides monitoring in different environmental samples.

Host-Guest Recognition of Pesticides by Calixarenes

This article is based on a review of the literature and our own experience with toxicological molecules. We explain the nature of calix[n]arenes and as their recognized properties are used to detect compounds of toxicological interest, mainly the most important pesticide families such as organophosphorated, organochlorine compounds, pyrethroid insecticides, carbamate fungicides, and herbicides, using different techniques. In addition, we show the role of the macrocycle and its interactions, and the advantage of using this type of compound for improving conventional techniques, where the phenomenon of recognition is very important, such as chromatography, solid-phased extraction, and the development of specific sensors, among others and Even we also show the use of this macrocycle for detoxication procedures in vivo. In this way, we display as the multiple possibilities of functionalization of the calix[n]arenes makes these versatile molecules in the phenomena of specific recognition. Finally, This review highlights the main analytical methods reported in the literature for determination of plaguicides by host-guest interaction with calixarenes. In this way, among the available analytical tools, chromatographic, and electrochemical-based methods are the most used techniques for the detection and to quantify plaguicides using calixarenes.

Highly selective amino-functionalized magnetic molecularly imprinted polymers: absorbents for dispersive solid phase extraction and trace level analysis of chlorophenols in seawater

Three-in-one dispersive magnetic solid phase extraction system for preconcentration of trace-level CPs in seawater was established by using as-prepared molecularly imprinted magnetic polymers with effective, fast, and accurate for routine analyses.

Methodologies for the extraction of phenolic compounds from environmental samples: new approaches

Phenolic derivatives are among the most important contaminants present in the environment. These compounds are used in several industrial processes to manufacture chemicals such as pesticides, explosives, drugs and dyes. They also are used in the bleaching process of paper manufacturing. Apart from these sources, phenolic compounds have substantial applications in agriculture as herbicides, insecticides and fungicides. However, phenolic compounds are not only generated by human activity, but they are also formed naturally, e.g., during the decomposition of leaves or wood. As a result of these applications, they are found in soils and sediments and this often leads to wastewater and ground water contamination. Owing to their high toxicity and persistence in the environment, both, the US Environmental Protection Agency (EPA) and the European Union have included some of them in their lists of priority pollutants. Current standard methods of phenolic compounds analysis in water samples are based on liquid–liquid extraction (LLE) while Soxhlet extraction is the most used technique for isolating phenols from solid matrices. However, these techniques require extensive cleanup procedures that are time-intensive and involve expensive and hazardous organic solvents, which are undesirable for health and disposal reasons. In the last years, the use of news methodologies such as solid-phase extraction (SPE) and solid-phase microextraction (SPME) have increased for the extraction of phenolic compounds from liquid samples. In the case of solid samples, microwave assisted extraction (MAE) is demonstrated to be an efficient technique for the extraction of these compounds. In this work we review the developed methods in the extraction and determination of phenolic derivatives in different types of environmental matrices such as water, sediments and soils. Moreover, we present the new approach in the use of micellar media coupled with SPME process for the extraction of phenolic compounds. The advantages of micellar media over conventional extractants are reduction of organic solvent, low cost, easy handling and shorter time procedures.

Correlations and predictions of carboxylic acid pKa values using intermolecular structure and properties of hydrogen-bonded complexes

Density functional theory calculations have been preformed on a series of hydrogen-bonded complexes of substituted aliphatic and aromatic carboxylic acids with ammonia. Molecular properties, particularly those related to hydrogen bonding, have been carefully examined for their interdependence as well as dependence on the acidity of the acid. The bond length and stretching frequency of the hydroxyl group and the hydrogen-bond length and energy of the complex are shown to be highly correlated with each other and are linearly correlated with available literature pKa values of the carboxylic acids. The linear correlations resulting from the fit to the available pKa values can be used to predict the pKa values of similar carboxylic acids. The pKa values so predicted using the different molecular properties are highly consistent and in good agreement with the literature values. This study suggests that calculated molecular properties of hydrogen-bonded complexes allow effective and systematic prediction of pKa values for a large range of organic acids using the established linear correlations. This approach is unique in its capability to determine the acidity of a particular functional group or the local acidity within a large molecular system such as a protein.

Theoretical study of hydrogen-bonded complexes of chlorophenols with water or ammonia: Correlations and predictions of pKa values

A simple practical method for predicting the acidity constants (as pKa values) of chlorophenols is proposed based on density functional theory calculations of a series of hydrogen-bonded complexes of phenol and 19 different congeners of chlorophenol, with a single probe molecule, either water or ammonia. Relevant structural parameters and molecular properties of these complexes, primarily involving the acidic hydroxyl group, are examined and plotted against the known pKa values of 14 chlorophenols and phenol. Strong linear correlations are found for these compounds. Such correlations are used to determine the pKa values of five chlorophenols whose experimental acidities have large uncertainties. Similar predicted pKa values are obtained by using different structural parameters and molecular properties for the complexes with either probe molecule. The study may be extended to determine the acidity of other compounds with a single acidic functional group.

A sensitive solid-phase microextraction/gas chromatography-based procedure for determining pentachlorophenol in food

A new method for the determination of pentachlorophenol (PCP) in different foods was developed using capillary gas chromatography (GC) and microwave induced-plasma atomic emission spectrometry (MIP-AED). The analyte is first derivatized and then extracted and pre-concentrated by solid-phase microextraction (SPME) in headspace (HS) mode. A clear matrix effect was found for the different samples investigated, so that standard addition was required for quantification. Detection limits of 0.03-6.0 ng g(-1) were obtained, depending on the sample analysed. The method gave recoveries of 81-109% from spiked samples. Concentration levels of PCP ranged from 0.3 to 1.5 ng g(-1) were found in honey, but no PCP was detected in other samples.

Recent developments in headspace microextraction techniques for the analysis of environmental contaminants in different matrices

Headspace microextraction procedures such as solid-phase microextraction (SPME) and single drop microextraction (SDME) or liquid-phase microextraction (LPME) are increasingly used for the extraction of environmental organic pollutants from a variety of aqueous, viscous, semisolid and solid environmental and biological matrices. In this article, recent analytical applications of these methodologies when used as an isolation and trace enrichment step prior to the analysis of organic pollutants (pesticides, polycyclic aromatic hydrocarbons, polychlorinated compounds, organotin compounds, phenolic derivatives, aromatic amines, phthalates, etc.) by gas and liquid chromatography are reviewed. The applicability and inherent limitations of headspace microextraction are also discussed. The future direction of research in this field and general trends toward commercial applications are considered.

Spectrofluorimetric Determination of Pentachlorophenol Based on Its Inhibitory Effect on The Redox Reaction Between Hydroxyl Radicals and Fluorescent Dye Rhodamine B

Hydroxyl radicals that is generated by Fenton reagent reacts with rhodamine B, which makes the fluorescence quenching of rhodamine B. However, there is an inhibitory effect of pentachlorophenol on the reaction. Based on this observation, an inhibitory fluorimetric method is reported for the determination of trace pentachlorophenol. The fluorescent inhibition of rhodamine B is measured by fix-time method. On the optimum conditions of experimentation, the detection limit for pentachlorophenol is 3.0 ng/ml and the linear range of the determination is 4.0-240 ng/ml. Combined with the samples treating with ion exchange resins and XDA-1 absorption resin, the method has been used for the determination of pentachlorophenol in synthetic samples and natural water samples with satisfactory results. We have also discussed the possible mechanism of the reaction.

A fluorimetric method for the determination of trace pentachlorophenol, based on its inhibitory effect on the redox reaction between the improved Fenton reagent and rhodamine B

A sensitive fluorimetric method is presented and discussed for the determination of pentachlorophenol in aqueous solutions. This method is based on the inhibitory effect of pentachlorophenol on the reaction of conventional Fenton [Fe(III) + H(2)O(2)] reagent with rhodamine B in the medium of perchloric acid, which results in the fluorescence quenching of rhodamine B. It was further found that the sensitivity for the determination was improved significantly when the molecular ligand EDTA was added. This improved system was therefore presented for the determination of pentachlorophenol. The characteristics of the excitation and emission spectra, optimization of the experimental conditions, the stability of the system and the influence of foreign matter have all been investigated. Under optimal conditions, the linear range for the determination of pentachlorophenol is 12-480 ng/mL with a 3sigma limit of detection of 0.96 ng/mL. Compared with the conventional Fenton system, the improved system shows obvious advantages in both sensitivity and selectivity. By combination with the pretreatment of samples using ion exchange resins and XDA-1 absorption resin, the improved Fenton method was used for the first time for the determination of pentachlorophenol in synthetic samples and natural water samples, and satisfactory results, in agreement with those of the HPLC method, were achieved. The possible mechanism of the reactions has also been discussed.

Evaluation of solid-phase microextraction conditions for the determination of chlorophenols in honey samples using gas chromatography

A rapid and solvent-free method for the determination of nine chlorophenol (CP) compounds in honey samples using headspace solid-phase microextraction (HS-SPME) and gas chromatography with atomic emission detection (GC-AED) is developed. The different factors affecting the efficiency of the extraction and derivatization steps were carefully optimized. The polydimethylsiloxane-divinylbenzene (PDMS/DVB) fiber was the most suitable for preconcentrating the analytes from the headspace of an aqueous solution containing the dissolved honey samples where the chlorophenols had been submitted to acetylation. When the matrix effect was evaluated for different samples, it was concluded that standard addition calibration was required for quantification purposes. Detection limits roughly ranged from 0.1 to 2.4 ng g(-1), depending on the compound and the honey sample analyzed, with a fiber time exposure of only 15 min at 75 degrees C. The optimized method was successfully applied to different samples, some of the studied chlorophenols being detected in some of the analyzed honeys at concentration levels 0.6-9.4 ng g(-1).

Coupling of headspace solid phase microextraction with ultrasonic extraction for the determination of chlorinated pesticides in bird livers using gas chromatography

In the present study a combined analytical method involving ultrasonic extraction (USE), sulfuric acid clean-up and headspace solid-phase microextraction (HS-SPME) was developed for the determination of chlorinated pesticides (CPs) in bird livers. Extraction of CPs from 1g of liver was performed by ultrasonication for 30 min using 20 mL of solvent mixture (n-hexane:acetone (4:1, v/v)). The extract was subsequently subjected to a clean-up step for lipid removal. A comparative study on several clean-up procedures prior to the HS-SPME enrichment step was performed in order to achieve maximum recovery and optimal clean-up efficiency, which would provide suitable limits of detection in the gas chromatographic analysis. For this purpose, destructive (sulfuric acid or sodium hydroxide treatment) and non-destructive (alumina column) clean-up procedures has been assayed. The treatment of the extract with 40% (v/v) H2SO4 prior to HS-SPME process showed the best performance since lower detection limits and higher extraction efficiencies were obtained. The method detection limit ranged from 0.5 to 1.0 ng g(-1) wet weight and peak areas were proportional to analyte concentrations (r2>0.990) in the range of 5-500 ng g(-1) wet wt. The method was found to be reproducible (R.S.D.<10%) and effective under the operational conditions proposed and was applied successfully to the analysis of CPs in liver tissues of various bird species from Greece.

SPME in environmental analysis

Recent advances in the use of solid-phase microextraction (SPME) in environmental analysis, including fiber coatings, derivatization techniques, and in-tube SPME, are reviewed in this article. Several calibration methods for SPME, including traditional calibration methods, the equilibrium extraction method, the exhaustive extraction method, and several diffusion-based calibration methods, are presented. Recent developed SPME devices for on-site sampling and several applications of SPME in environmental analysis are also introduced.