Determination of polycyclic aromatic hydrocarbons in seawater by high-performance liquid chromatography with fluorescence detection following micelle-mediated preconcentration

Ribbon-shaped supramolecular solvents: Synthesis, characterization and potential for making greener the microextraction of water organic pollutants

Liquid-liquid microextraction (LLME) techniques have experienced a tremendous growth over the last years but still face major challenges related to the use of more efficient and environmentally friendly solvents. Supramolecular solvents (SUPRASs) have proved outstanding efficiency in LLME, but many of the experimental conditions required for SUPRAS formation and/or application cannot be considered green or experimentally convenient. This paper was intended to make greener both SUPRAS formation and their application to the LLME of low-concentration organic pollutants in environmental waters. For this purpose, a variety of SUPRASs were produced at room temperature by simply mixing alkyl phosphonates (A_6-12PO₃H^- and A_6-12PO₃^-2) and tetrahexylammonium (He₄N⁺) ions in aqueous media. Among them, the SUPRASs produced from decyl hydrogen phosphonate (DePO₃H^-) and He₄N⁺ allowed, for the first time, the development of SUPRAS-based LLMEs where the SUPRAS previously synthesized was added to the liquid sample, instead of being formed in situ as usual, which was proved particularly advantageous for analyses involving large sample/SUPRAS volume ratios. At near equimolar amounts of DePO₃H^- and He₄N⁺, the amphiphile arranged in the SUPRAS as planar ribbons consisting of water (21 ± 3%, w/v) and DePO₃H^- and He₄N⁺ in the concentration range 1.0-1.4 M. The application of these SUPRASs to LLMEs was proved by extracting carcinogenic polycyclic aromatic hydrocarbons (CPAHs) from drinking (tap and bottled) and natural (river, reservoir and underground) water (recoveries between 84 and 117% with standard deviations varying between 1 and 14%). The developed method was simple (it only required the addition of 500 μL of SUPRAS to 75 mL of sample, stirring and centrifugation), sensitive (method quantitation limits were below the maximum allowed limits set by the EU; were 0.6-7.1 ng L^-1) and selective (SUPRAS extracts were directly analyzed by liquid chromatography-fluorimetry). This research proves that SUPRASs can be operationally used in LLMEs similarly to conventional solvents, which should favor their routine application in high-sample throughput laboratories.

Dual-Purpose SERS Sensor for Selective Determination of Polycyclic Aromatic Compounds via Electron Donor-Acceptor Traps

Toxic, carcinogenic, and mutagenic properties of polycyclic aromatic hydrocarbons (PAHs) and environmental pollution caused by polycyclic aromatic sulfur heterocycles (PASHs) postulate the importance of their selective and sensitive determination in environmental and oil fuel samples. Surface-enhanced Raman spectroscopy (SERS) opens up an avenue toward multiplex analysis of complex mixtures, however not every molecule gives high enhancement factors and, thus, cannot be reliably detected via SERS. However, the sensitivity can be drastically increased by additional resonant enhancement as a result of the analyte absorption band overlapping with the surface plasmon band of nanoparticles (NPs) and the laser excitation wavelength. Using this idea, we developed a dual-purpose SERS sensor based on trapping the target PAHs and PASHs into colored charge-transfer complexes (CTCs) with selected organic π-acceptor molecules on the surface of AgNPs. Studying, computing, and then comparing stability constants of the formed CTC served as a powerful explanation and prediction tool for a wise choice of π-acceptor indicator systems for the further silver surface modification. Moreover, we show that CTC formation can be effectively utilized for increasing both selectivity and sensitivity by simple liquid-liquid extraction prior to SERS measurements. For the first time, the dual-purpose SERS sensor allowed determination of two different classes of polycyclic aromatic fuel components down to 10 nM concentration, lower than that restricted by the ASTM regulation, and demonstrated multi-purpose capabilities of the developed approach.

Twenty years of supramolecular solvents in sample preparation for chromatography: achievements and challenges ahead

Supramolecular solvents (SUPRAS) have progressively become a suitable alternative to organic solvents for sample preparation in chromatographic analysis. The inherent properties of these nanostructured solvents (e.g. different polarity microenvironments, multiple binding sites, possibility of tailoring their properties, etc.) offer multiple opportunities for the development of innovative sample treatment platforms not approachable by conventional solvents. In this review, major achievements attained in the combination SUPRAS-chromatography in the last 20 years as well as the challenges that should be addressed in the near future are critically discussed. Among achievements, particular attention is paid to the theoretical and practical knowledge gained that has helped make substantial progress in the area. In this respect, advances in the understanding of the mechanisms involved in SUPRAS formation and SUPRAS-solute interactions driving extractions are discussed, with a view to the setting up of knowledge-based extraction procedures. Likewise, the strategies followed to improve the compatibility of SUPRAS extracts with liquid and gas chromatography and adapt SUPRAS-based extractions to different formats are presented. Ongoing efforts to apply SUPRAS in multicomponent extractions and synthesize tailored SUPRAS for the development of innovative sample treatments are highlighted. Among challenges identified, discussion is focused on the automation of SUPRAS-based sample treatment and the elucidation of SUPRAS nanostructures, which are considered essential for their acceptance in routine labs and the design of tailored SUPRAS with programmed functions. Graphical abstract.

In Situ Miniaturised Solid Phase Extraction (m-SPE) for Organic Pollutants in Seawater Samples

Solid phase extraction (SPE) is a consolidated technique for determining pollutants in seawater samples. The current tendency is to miniaturise systems that extract and determine pollutants in the environment, reducing the use of organic solvents, while maintaining the quality in the extraction and preconcentration. On the other hand, there is a need to develop new extraction systems that can be fitted to in situ continual monitoring buoys, especially for the marine environment. This work has developed a first model of a low-pressure micro-SPE (m-SPE) for persistent organic pollutants (POPs) that can be simply applied to in situ monitoring in the marine environment. This system reduces the volumes of sample and solvents required in the laboratory in comparison with conventional SPE. In the future, it could be used in automated or robotic systems in marine technologies such as marine gliders and oceanographic buoys. This system has been optimised and validated to determine polycyclic aromatic hydrocarbons (PAH) in seawater samples, but it could also be applied to other kinds of persistent organic pollutants (POPs) and emerging pollutants.

Mixed micelles-mediated dephenolisation of table olive processing's wastewaters

Olive processing wastewaters account for highly pollutant agro-industrial effluents. Their phenolic compounds are responsible for their toxicity. Those natural compounds have to be degraded or recovered before any discharge into the environment. This investigation deals with the extraction and concentration of the phenolic compounds into an aqueous phase using a mixture of nonionic/anionic surfactants. A synergistic effect for the extraction of the natural phenolic compounds was observed when Genapol X-80 was combined with sodium dodecyl sulphate (SDS). For the tested Genapol X-80 concentration (1-5%), a minimum concentration of 2.5 mM SDS was demonstrated to be necessary to reach maximum extraction rates. The extraction efficiencies were only slightly affected by temperatures between 20 and 50 °C. However, the recovery rate of the phenolic compounds increased with the augmentation of the contact time. The pH has also been found to greatly influence the extraction of the phenolic compounds and the coacervate volume fraction. At optimal conditions, the coacervate phase was enriched up to four times whereas the maximum reduction of the phenolic content in the diluted phase reached more than 40% in one step extraction.

Cloud Point Extraction of Polycyclic Aromatic Hydrocarbons in Aqueous Solution with Nonionic Surfactants

A cloud point extraction (CPE) process using the two nonionic surfactants, Tergitol 15-S-9 and Tergitol 15-S-7, mixtures of secondary ethoxylated alcohols, to extract selected polycyclic aromatic hydrocarbons (PAHs) from aqueous solutions at 25°C was investigated. Cloud point temperatures (CPTs) of selected nonionic surfactants were studied against the effect of added electrolytes on their cloud points. Sodium iodide could increase the cloud points of selected nonionic surfactants, i.e., the salt-in effect, whereas sodium chloride, sodium phosphate and sodium sulfate could decrease the cloud point, i.e., the salt-out effect. Cloud point temperatures (CPTs) of these micellar solutions were regulated and reduced enough with addition of sodium phosphate and sodium sulfate, so that the cloud point extraction (CPE) process could be facilitated at 25°C. It was found that a higher preconcentration factor could be achieved in the micellar solution having a lower surfactant concentration. The average preconcentration factor was also discussed as a function of surfactant concentration used in the CPE process.

Determination of light-medium-heavy polycyclic aromatic hydrocarbons in vegetable oils by solid-phase extraction and high-performance liquid chromatography with diode array and fluorescence detection

A new method for determination of 16 polycyclic aromatic hydrocarbons (PAHs)-naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene, benzo[g,h,i]perylene, and indeno[1,2,3-cd]pyrene-in vegetable oils was developed. Solid-phase extraction (SPE) prior to high-performance liquid chromatography with fluorescence detection could be used for all those PAHs except acenaphthylene. Acenaphthylene could be detected using a diode array detector at 228 nm. The parameters and variables that affect the extraction were investigated. Under optimum conditions: the extract reagent was centrifuged at 4 °C and evaporated. After that a SPE procedure was used for further cleanup. The limits of detection and limits of quantification were in the range of 0.01-2.35 and 0.04-7.00 μg kg(-1) in vegetable oil, respectively. The relative standard deviations were under 5%.

Determination of phenoxy herbicides in water samples using phase transfer microextraction with simultaneous derivatization followed by GC-MS analysis

A sensitive and accurate method for the determination of two model phenoxy herbicides, 4-chloro-2-methylphenoxy acetic acid and 4-chloro-2-methylphenoxy propanoic acid, in water is explained. This method utilizes a simple phase transfer catalyst-assisted microextraction with simultaneous derivatization. Factors affecting the performance of this method including pH of the aqueous matrix, temperature, extraction duration, type and amount of derivatization reagents, and type and amount of the phase transfer catalyst are examined. Derivatization and the use of phase transfer catalyst have proven to be especially vital for the resolution of the analytes and their sensitive determination, with an enrichment factor of 288-fold for catalyzed over noncatalyzed procedure. Good linearity ranging from 0.1 to 80 μg L(-1) with correlation of determination (r(2) ) between 0.9890 and 0.9945 were obtained. Previous reported detection limits are compared with our new current method. The low LOD for the two analytes (0.80 ng L(-1) for 4-chloro-2-methylphenoxy propanoic acid and 3.04 ng L(-1) for 4-chloro-2-methylphenoxy acetic acid) allow for the determination of low concentrations of these analytes in real samples. The absence of matrix effect was confirmed through relative recovery calculations. Application of the method to seawater and tap water samples was tested, but only 4-chloro-2-methylphenoxy propanoic acid at concentrations between 0.27 ± 0.01 and 0.84 ± 0.06 μg L(-1) was detected in seawater samples.

Use of coacervates for the on-site extraction/preservation of polycyclic aromatic hydrocarbons and benzalkonium surfactants

The suitability of coacervates for the preservation of organic pollutants after their extraction from water samples was investigated for the first time. Acid-induced sodium dodecanesulfonic acid (SDSA) micelle-based coacervates were selected for this purpose. Their capacity to preserve benzalkonium homologue (C(12), C(14) and C(16)) surfactants (BASs) and different polycyclic aromatic hydrocarbons (PAHs) [benzo(a)pyrene (BaP), benzo(b)fluoranthene (BbF), benzo(k)fluoranthene (BkF), benzo(ghi)perylene (BghiP), benzo(a)anthracene (BaA) and indene(1,2,3-c-d)pyrene (IP)] was investigated. BASs and PAHs were efficiently extracted by the coacervate by formation of mixed aggregates and hydrophobic interactions, respectively. Their stability into the coacervate was investigated under three temperature conditions (room temperature, 4 degrees C and -20 degrees C) and two hydrochloric acid concentrations (3.75 M and 4.2 M), which was used to induce coacervation. No losses were observed during at least 3 months at the different experimental conditions tested. The increase of the temperature up to 35 degrees C for a month did not affect the stability of the target compounds. No influence of the water matrix (distilled, river or wastewater) on the stabilization of BASs and PAHs was observed. The high-stabilizing capacity of the coacervate for the target compounds and its low volume make easy the transport and storage of analytes.

Cloud point extraction coupled with HPLC-UV for the determination of phthalate esters in environmental water samples

A method based on cloud point extraction was developed to determine phthalate esters including di-ethyl-phthalate (DEP), di-(2-ethylhexyl)-phthalate (DEHP) and di-cyclohexyl-phthalate (DCP) in environmental water samples using high-performance liquid chromatography separation and ultraviolet detection (HPLC-UV). The non-ionic surfactant Triton X-114 was chosen as extraction solvent. The parameters affecting extraction efficiency, such as concentrations of Triton X-114 and Na2SO4, equilibration temperature, equilibration time and centrifugation time were evaluated and optimized. Under the optimum conditions, the method can achieve preconcentration factors of 35, 88, 111 and detection of limits of 2.0, 3.8, 1.0 ng/ml for DEP, DEHP and DCP in 10-ml water sample, respectively. The proposed method was successfully applied to the determination of trace amount of phathalate esters in effluent water of the wastewater treatment plant and the lixivium of plastic fragments.

Determination of some polycyclic aromatic hydrocarbons in filter tar of Turkish cigarettes

A simultaneous determination method for the analysis of benzo[a]pyrene (BaP) and dibenzo[a,h]anthracene (DahA) in the filter tar of Turkish cigarettes has been developed. The method involved (a) the extraction of BaP and DahA with n-hexane from ACN solution in which the cigarette filters were extracted, and then (b) purification of the n-hexane extracts by elution on an XAD-2 column using n-hexane/dichloromethane (9:1, v/v) mixture. Separation and quantitative determination of BaP and DahA in the extracts were carried out by HPLC and fluorescence detection on a C18 RP column. The calculated recoveries for BaP and DahA were found in the range of 90-100% for each extraction and clean-up steps. Analysis of various filter tar of Turkish cigarettes showed that an average of 74.28 ng/filter of BaP and 5.24 ng/filter of DahA were present in Turkish cigarettes.

Development of a Model to Predict Partition Coefficient of Organic Pollutants in Cloud Point Extraction Process

A quantitative structure property relationship (QSPR) study has been performed to establish a model to relate structural descriptors of 45 organic compounds to their partition coefficients in water-hexadecylpyridinium chloride (CPC) micelles at 298K using partial least squares (PLS). 510 of six different categories of structural descriptors were calculated by Dragon software. The descriptors with 0.9 mutually pair correlations and with less than 0.1 with dependent variables were excluded at the early stage of the preprocessing of the structural data matrix. The data set was randomly divided into two groups: training set (40 molecules) and test set (5 molecules). In the final model 50 of the most effective of the structural descriptors on the partition coefficient were remained to model building by PLS calibration method. The optimum number of latent variables 5, which spanned 80% of the original variations of data matrix, was selected using leave one out cross validation method. Prediction ability of the model was tested by prediction of the partition coefficients of five unknown compounds and the mean relative error of prediction was 3.6%. The outliers were treated using leverage and score plots of the first third principal components. The efficiency of the new model was compared with Abraham model and it was found that the proposed model has more prediction ability.

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.

Comparison of traditional cloud-point extraction and on-line flow-injection cloud-point extraction with a chemiluminescence method using benzo[a]pyrene as a marker

In this work, using benzo(a)pyrene (BaP) as marker, the analytical merits of on-line flow-injection cloud-point extraction (FI CPE), including preconcentration factor, extraction efficiency, sample throughput, and analysis time were evaluated by use of peroxyoxalate chemiluminescence (CL) detection. Moreover, by detailed discussion of several preconcentration conditions for traditional and on-line FI CPE the advantages of on-line FI CPE became conspicuously apparent. When coupled with separation techniques such as high-performance liquid chromatography (HPLC) or capillary electrophoresis (CE), on-line FI CPE-CL has much potential for analysis of low concentrations of polycyclic aromatic hydrocarbons (PAH) in environmental samples.

Determining PAHs and PCBs in aqueous samples: finding and evaluating sources of error

This work describes the problems that occur during routine multi-step determinations of polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), which can be present at trace levels in water, and identifies sources of analyte losses at particular steps during the analytical procedure. PAH and PCB adsorption onto the walls of the container ranged from 0 to 70%. PAH and PCB recoveries of >70% were achieved during the LLE and SPE extraction steps. During the process of enriching the dichloromethane extract with PAHs and PCBs, based on the gentle evaporation of solvent, losses were <24% and <19%, respectively. Model experiments show that neither isolation of PAHs and PCBs (performed using either LLE or SPE) nor extract enrichment reduce the reliability of PAH and PCB determination. The steps that lead to the greatest loss of analyte are the ones that involve sampling, transport and storage of the water samples.

Coupling micelle-mediated extraction using mixtures of surfactants and fluorescence measurements with a fiber-optic for the screening of PAHs in seawater

The screening of PAHs from seawater samples using cloud-point extraction (CPE) as a step prior to their determination by fluorescence measurements with a fiber-optic is proposed. The CPE is carried out with the nonionic surfactants mixture POLE and Brij 30. The fluorescence measurement parameters were optimized, allowing selection of benzo(a)pyrene (B(a)Py) and benzo(k)fluoranthene (B(k)Ft) as the target analytes for the screening. The reproducibility of the whole screening system, expressed as relative standard deviation, was 9.0% for B(a)Py and 12.1% for B(k)Ft (both for n = 7). The reliability of the method was established at five concentrations for B(a)Py (between 0.5 and 3.3 times the detection limit: 0.31 ng ml(-1)) and at three concentrations for B(k)Ft (between 0.6 and 2.5 times the detection limit: 0.56 ng ml(-1)). The resolution of binary mixtures of these PAHs at different levels of concentration, and a study of the interferences with the rest of the PAHs were also carried out.

Prediction of the behaviour of organic pollutants using cloud point extraction

A preconcentration study based on the cloud point phenomenon was carried out for a set of triazine herbicides, three of them chloro-substituted and three of them methylthio-substituted. Concentration factors and recoveries were calculated as function of the percentage of the non-ionic surfactant Triton X-114 employed. From these values, obtained from a cloud point extraction (CPE) procedure, the distribution coefficient between the Triton X-114 micelles and water, Kc, prior to CPE was calculated for each triazine and related to the corresponding octanol-water partition coefficient, Kow. In order to confirm the results obtained with the triazine herbicides, two sets of data from chemically different organic pollutants--organophosporous and chlorophenols--obtained from the literature were assessed, concluding that they display a similar behaviour to that of the triazine herbicides. This can be used to predict the CPE behaviour of other organic pollutants from their octanol-water partition coefficients. The Kc values were compared with the analyte concentration ratio in the surfactant-rich phase and aqueous phase (Ksa) with a view to obtaining a link between the analyte behaviour prior to and after cloud point extraction procedures.

POE chain length selectivity in the clouding of a triton surfactant

The POE chain length distribution between the coacervate and aqueous phases of a clouded Triton X-114 solution was studied. The average chain length of the surfactant in the aqueous layer was determined by HPLC and compared to the distribution in the original (unclouded) solution. Both the clouding temperature and the equilibration time were found to govern the chain length selectivity. A slight excess of longer POE chains were encountered in the aqueous layer, thus enriching the coacervate layer with shorter, less soluble chains. Chain length selection appeared to occur when the surfactant particles were dispersed in the clouded suspension, rather than after the establishment of the aqueous and coacervate layers.

Acid-induced cloud point extraction and preconcentration of polycyclic aromatic hydrocarbons from environmental solid samples

The effectiveness of the acid-induced phase separation of anionic surfactants (acid-induced cloud point extraction, ACPE) to extract polycyclic aromatic hydrocarbons (PAHs) from different environmental samples (soils, sediments and sludges), prior to chromatographic analysis, was evaluated. Variables affecting the ACPE efficiency were optimised using a natural matrix (a harbour sediment, CRM 535). Temperature, surfactant concentration and stirring were of primary importance to maximise recovery, whereas temperature and surfactant/hydrochloric acid concentration influenced the volume of the surfactant-rich phase and therefore the preconcentration factor achieved. The optimal conditions (2% sodium dodecanesulphonate (SDoS), 4.2 M HCl, 60 degrees C, 1 h) were applied to the extraction of PAHs from various matrices and the ACPE recoveries compared to certified results from Soxhlet extractions. Recoveries obtained for four to five aromatic ring PAHs ranged from 71 to 98%. Uncertainties obtained using ACPE were similar to or lower than those provided for the certified values. The volume of the extracts ranged from 1 to 2 ml. The method did not require additional clean-up or preconcentration steps.