An in-situ extraction-preconcentration method using ionic liquid-based surfactants for the determination of organic contaminants contained in marine sediments.

The determination of a group of organic contaminants from marine sediments samples including three polycyclic aromatic hydrocarbons, five alkylphenols (i.e., bisphenol-A or nonylphenol) and one paraben has been carried out using an extraction/preconcentration strategy with ionic liquid-based surfactants and high-performance liquid chromatography (HPLC) with diode array detection (DAD). Sediments are first extracted using two IL-based surfactants, specifically 1-hexadecyl-3-methyl imidazolium bromide (C(16)MIm-Br) and 1-hexadecyl-3-butyl imidazolium bromide (C(16)C(4)Im-Br), as the extraction media in a microwave-assisted extraction (MAE) procedure, followed by a novel in situ preconcentration method. The optimized MAE method requires 0.1 g of sediment and 5 mL of 40 mM C(16)MIm-Br IL solution. The extracts are then centrifuged and filtered. The subsequent preconcentration in situ approach consists of the insolubilization of an IL-based surfactant formed by a metathesis reaction using the anion-exchange reagent lithium bis[(trifluoromethane)sulfonyl]imide (LiNTf(2)), which produces an analyte enriched IL microdroplet. The optimized in situ approach utilizes 4 mL of the filtered extract, which are mixed with acetonitrile and 92 µL of LiNTf(2) solution (0.5 g mL(-1)), heated, vortexed and centrifuged. The formed IL microdroplet is then simply diluted with acetonitrile (~100 µL) and injected in the chromatograph without any further clean-up steps. The overall extraction/preconcentration method requires approximately 25 min in spite of dealing with complex solid samples, is nearly free of organic solvent (requires ~900 µL of acetonitrile per sample), and produces high preconcentration factors and quantification limits down to 0.04 mg kg(-1) using HPLC-DAD.

A novel preconcentration strategy for extraction methods based on common cationic surfactants: an alternative to classical coacervative extraction.

A novel and simple preconcentration step for aqueous micellar solutions of the common cationic surfactant cetyltrimethylammonium bromide (CTAB) has been developed. The procedure is based on the formation of another phase (a micro-droplet), not soluble in water, in which analytes (originally present in the aqueous solution) experience preconcentration. The method resembles to that of classical coacervation, but it does not require high ionic strengths neither acidic pH values. The optimum method implies mixing aqueous micellar solutions of CTAB with lithium bis[(trifluoromethane)sulfonyl]imide (Li-NTf2) in a 1:1 molar ratio with a 16.5% (v/v) of acetonitrile content, followed by vortex, heating at 65 °C during 2 min, and centrifugation. The obtained microdroplet containing analytes is then subjected to high-performance liquid chromatography (HPLC) with diode-array detection (DAD). The method has been applied to the determination of a group of organic contaminants including alkylphenols, polycyclic aromatic hydrocarbons and parabens, present in aqueous samples (including seawater) or solid samples (such as sediment samples, which are subjected to a previous microwave-assisted extraction). Average preconcentration factors of roughly 14 and 12 are obtained for aqueous and sediment samples, respectively; being the limits of quantification down to 0.5 µg L⁻¹ and 0.02 mg kg⁻¹, respectively.

Suitability of ionic liquids as mobile-phase additives in HPLC with fluorescence and UV detection for the determination of heterocyclic aromatic amines.

The effects of several ionic liquids (ILs) as mobile-phase additives in HPLC with fluorescence and UV-Vis detection for the determination of six heterocyclic aromatic amines were evaluated using two different C(18) stationary phases with moderate silanol activity. The studied ILs were 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate and 1-methyl-3-octylimidazolium tetrafluoroborate. The optical behaviour of heterocyclic aromatic amines in presence of ILs was studied and the silanol-suppressing potency of ILs was evaluated for the two stationary phases studied. Several chromatographic parameters were evaluated in the presence or absence of ILs, or using triethylamine, the most common mobile-phase additive. The best results were achieved using 1 mM 1-butyl-3-methylimidazolium tetrafluoroborate as mobile-phase additive and NovaPak column. In these conditions and with 18% of ACN in the mobile phase, analytical performance of the chromatographic methods using fluorescence and UV-Vis were evaluated, obtaining good precision in all cases (RSD lower than 6.6%) and low LOD (0.001-0.147 microg/mL with UV-Vis and 0.001-0.006 ng/mL with fluorescence detection).

Ionic liquids as mobile phase additives in high-performance liquid chromatography with electrochemical detection: application to the determination of heterocyclic aromatic amines in meat-based infant foods.

The beneficial effects of several ionic liquids (ILs) as mobile phase additives in high-performance liquid chromatography with electrochemical detection for the determination of six heterocyclic aromatic amines (HAs) have been evaluated for first-time. The studied ionic liquids were 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF(4)), 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIm-BF(4)) and 1-methyl-3-octylimidazolium tetrafluoroborate (MOIm-BF(4)). Several chromatographic parameters have been evaluated in the presence or absence of ILs, or using ammonium acetate as the most common mobile phase additive, with three different C18 stationary phases. The effect of the acetonitrile content was also addressed. In general, best resolution, lower peak-widths (up to 72.1% lower) and lower retention factors are obtained when using ILs rather than ammonium acetate as mobile phase additives. The main improvement was obtained in the baseline noise, being 360% less noisy for BMIm-BF(4), 310% for HMIm-BF(4), and 227% for MOIm-BF(4), when compared to ammonium acetate at +1000 mV. Different chromatographic methods using the best conditions for each IL were also evaluated and compared. Finally, the best chromatographic conditions using 1mM of BMIm-BF(4) as mobile phase additive, the Nova-Pak C18 column, 19% (v/v) of acetonitrile content in the mobile phase, and +1000 mV in the ECD, have been applied for the chromatographic analysis of six HAs contained in meat-based infant foods. The whole extraction method of meat-based infant foods using focused microwave-assisted extraction and solid-phase extraction has also been optimized. Extraction efficiencies up to 89% and detection limits ranged between 9.30 and 0.165 ng g(-1) have been obtained under optimized conditions.

Determination of carbonyl compounds in smoke samples: strategies for sampling and standardization.

There are significant drawbacks to the calibration procedure recommended in the normalized Spanish or American methods used to determine carbonyl compounds in ambient air by quantifying hydrazones that form with 2,4-dinitrophenylhydrazine. The impurities present in 2,4-dinitrophenylhydrazine, as well as the lack of quantitativity and the slow kinetics of some derivatization reactions can lead to considerable errors in quantification. This work proposes two alternative systems for sampling biomass smoke in order to analyze aldehydes and ketones. The standardization process used by both systems requires standard solutions to be reacted with 2,4-dinitrophenylhydrazine under experimental conditions similar to those used to collect the sample. The resulting calibration curve slopes differ between 8% and 74% from the curves used in methods that employ commercial standard hydrazone solutions. The detection limits reached by using the proposed methods are between 0.07 and 0.47 mg L(-1). Both methods are complementary for smoke samples that have significant differences in the concentrations of aldehydes or ketones.

Ionic liquids as desorption solvents and memory effect suppressors in heterocyclic aromatic amines determination by SPME-HPLC fluorescence.

The beneficial effects of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF(4)) ionic liquid (IL) as mobile phase additive, desorption solvent, and memory effect suppressor in solid-phase microextraction (SPME)-high-performance liquid chromatography with fluorescence detection for the determination of six heterocyclic aromatic amines have been evaluated for the first time. Several chromatographic parameters have been evaluated in the presence or absence of IL or using triethylamine as the most common mobile phase additive, with a Nova-Pak C18 stationary phase. This IL was found to be clearly superior to triethylamine for efficiency as well as peak shape enhancement and sensitivity increase. SPME was chosen because it is faster than conventional extraction techniques and allowed us to minimize the use of organic solvents. However, memory effect may become a problem when a high-sensitivity detector is used. The appropriate conditions for the desorption step and to eliminate the memory effect involving BMIm-BF(4) were established and optimized. The method was applied for the determination of these compounds in commercial meat extracts.

Micelle-mediated extractions using nonionic surfactant mixtures and HPLC-UV to determine endocrine-disrupting phenols in seawaters.

An environmentally friendly method to extract endocrine-disrupting phenols (EDPs) from seawaters was realized using nonionic surfactant mixtures and micelle-mediated extractions. The preconcentration step was achieved directly in the seawater matrix, and was followed by high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection without any clean-up steps to remove the surfactant mixture prior to injection. Various nonionic surfactant mixtures were used, and polyoxyethylene-10-laurylether (POLE) with polyoxyethylene-4-laurylether (Brij 30) was found to be the best to work with. Method optimization involved maximizing the preconcentration factor using the studied mixtures. The proposed method gave extraction recoveries ranging from 83.3 to 114.4% for an EDP spiking level of 46.7 microg L(-1), and from 63.4 to 112.4% for a spiking level of 4.7 microg L(-1) for EDPs studied in real seawater matrices, with relative standard deviations of <12.1%. The detection limits of the method varied from 0.18 microg L(-1) for bisphenol A (BPA) to 1.17 microg L(-1) for 4-cumylphenol (4-CP). The method was applied to seawaters from the Canary Islands with successful results.

The ionic liquid 1-hexadecyl-3-methylimidazolium bromide as novel extracting system for polycyclic aromatic hydrocarbons contained in sediments using focused microwave-assisted extraction.

A method to extract PAHs from sediments is carried out using aqueous solutions containing aggregates of the ionic liquid (IL) 1-hexadecyl-3-methylimidazolium bromide (HDMIm-Br) as the extracting medium. Focused microwave-assisted extraction has been used to accelerate the extraction step, followed by HPLC with fluorescence detection without clean-up steps to remove the IL prior to injection. The method has been applied to certified reference sediment BCR-535 and marine sediments from Tenerife (Canary Islands) with successful results. The optimized method gave average absolute recoveries of 91.1% for six of the seven PAHs studied, with relative standard deviations lower than 10.4%. The overall method is characterized for presenting low extraction times (6min), low amounts of the sediment (0.1g), low amounts of IL (45mM), and low volumes of aqueous extractant solution (9mL). The use of small amounts of both IL and aqueous extractant solution allows the method to be considered environmental-friendly.

Characterization of humic substances of different origin by means of mass spectrometry and neural networks.

Mass spectrometry fingerprinting of humic acids extracted from different soils has been carried out using laser desorption/ionization mass spectrometry (LDI-TOF MS). LDI-TOF MS provides characteristic mass spectra fingerprints for the humic acids of different origin. The information given in the fingerprints was evaluated for natural grouping trends in the samples by neural networks computing tools, such as self-organizing feature map (SOFM). This approach is efficient for recognizing patterns in the humic acids samples independently of their characteristic variability; variability characterizing natural products such as humic substances. The use of multi-layer perceptron artificial neural networks gave a successful classification of the samples.

Focused microwave-assisted micellar extraction combined with solid-phase microextraction--gas chromatography/mass spectrometry to determine chlorophenols in wood samples.

This work describes the utilization of the focused microwave-assisted micellar extraction in combination with the solid-phase microextraction (SPME) to determine chlorophenols in wood samples. The influence of the nature of the surfactant in the extraction process, the optimization of the variables of the focused-microwave system, and the effect of the ageing time of the samples in the extraction efficiency of the method, have been assessed in this study. The overall method using the non-ionic surfactant POLE as extracting medium allows us to determine chlorophenols in wood samples achieving an average extraction efficiency of 104.1%, limits of detection ranging from 2 to 120 ng g(-1), and intermediate precision values ranging between 3.5 and 13.2%. The proposed method is also characterized by short analysis times (around 5 min for the microwaves extraction step) and by avoiding the use of organic solvents.

Determination of less polar heterocyclic amines in meat extracts: fast sample preparation method using solid-phase microextraction prior to high-performance liquid chromatography-fluorescence quantification.

A procedure for the determination of less polar heterocyclic amines in meat extracts using solid phase microextraction (SPME) coupled to high-performance liquid chromatography (HPLC) with fluorescence detection is presented. Analytes were first extracted from the samples using methanol/NaOH by an ultrasound-assisted method, and then concentrated on a Carbowax-templated resin (CW-TPR) SPME fiber. The extraction conditions such as extractant mixture composition, extraction time and extractions number, were optimized and the need of an extract freezing step previous to SPME is discussed. The detection limits under optimal conditions are in the range of 0.28-1.1 ng g(-1). The method was applied to the determination of less polar heterocyclic amines in four commercial meat extracts. Recovery values obtained are higher than 60% for the majority of amines.

Micellar solid-phase microextraction for determining partition coefficients of substituted polycyclic aromatic hydrocarbons in micellar media: possible prediction of hydrocarbon-micelle behaviour.

Micellar solid-phase microextraction (MSPME) coupled to gas chromatography-mass spectrometry (GC-MS) has been used to obtain partition coefficients of a group of 18 substituted aromatic hydrocarbons to ionic and nonionic micelles. Statistical and factor analyses have been utilized to establish some general equations relating molecular descriptors of non-substituted polycyclic aromatic hydrocarbons and their partition coefficients obtained by MSPME. The obtained equations have correlation coefficients higher than 0.94. They are used to predict hydrocarbon-micelle partition coefficients for a group of hydrocarbons with reported literature values giving a correlation coefficient of 0.98 and a standard deviation of the prediction of 0.182. The predictive model was also applied to substituted polycyclic aromatic hydrocarbons with partition coefficient values obtained by MSPME, with a 69% level of success.

Determination of the alkyl- and methoxy-phenolic content in wood extractives by micellar solid-phase microextraction and gas chromatography-mass spectrometry.

This work combines the utilization of the micellar media during the extraction step and the focused microwave-assisted extraction followed by the solid-phase microextraction-gas chromatography/mass spectrometry (SPME-GC/MS) to determine the alkyl- and methoxy-phenolic content in wood extractives. The proposed environmental-friendly method is mainly characterized by short analysis times (5min for the microwaves extraction step) and for avoiding the use of organic solvents. Different surfactants were tried for the extraction process: the cationic surfactant CTAB and the non-ionic surfactants Triton X-100 and POLE, with similar extraction efficiencies (85.5-99.7%). The overall method presents limits of detection in the ngg(-1) region for the alkylphenols (from 7 to 150ngg(-1)) and in the mugg(-1) region for the methoxyphenols (from 0.80 to 22.9mugg(-1)). The vanillin was the compound most abundant in the wood extractives studied, with concentrations up to 116.2mgkg(-1).

Optimization of an analytical methodology for the determination of alkyl- and methoxy-phenolic compounds by HS-SPME in biomass smoke.

A sampling and analysis method for the determination of 21 phenolic compounds in smoke samples from biomass combustion has been developed. The smoke is used to make smoked foods, following an artisanal procedure used in some parts of the Canary Islands. The sampling system consists of a Bravo H air sampler, two impingers, each one containing an aqueous solution of sodium hydroxide 0.1 mol L(-1), followed by a silica gel trap. The variables optimized to reach the best sampling conditions were volume of absorbent solution and sampling flow. Under the optimum conditions, 100 mL of absorbent solution of NaOH 0.10 mol L(-1) and 2 L min(-1) for the sampling flow, sampling efficiencies are higher than 80%. Analysis of phenolic compounds was carried out by headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography-mass spectrometry (GC-MS). Five different fiber coatings were employed in this study. By means of a central composite design, extraction time, salt concentration, and pH of the solution were optimized: 65-microm carbowax-divinylbenzene, extraction time 90 min, concentration in NaCl of 35% (m/v), and pH 2 yielded the highest response. Detection limits of phenol and their alkyl derivatives, guaiacol and eugenol, are between 1.13 and 4.60 ng mL(-1). 3-Methoxyphenol, 2,6-dimethoxyphenol, and vanillin have detection limits considerably higher. Good linearity (R2 > or = 0.98) was observed for all calibration curves in the established ranges. The reproducibility of the method (RSD, relative standard deviation) was found to oscillate between 7 and 18% (generally close or lower than 10%).

Study of the interactions between phenolic compounds and micellar media using micellar solid-phase microextraction/gas chromatography.

Solid-phase microextraction coupled to gas-chromatography with mass-spectrometry detection has been employed to establish the sensitivity indexes as well as to study the partition coefficients of phenols into ionic and nonionic micelles. The sensitivity indexes values can be used to estimate qualitatively the affinity between phenols and micelles. The studied phenols, some of them with high environmental interest, include chloro-, alkyl-, and methoxy-phenols. The results obtained in this work, using 85 microm polyacrylate fiber and anionic (sodium dodecyl sulphate), cationic (cetyltrimethylammonium bromide), and nonionic (Triton X-100 and polyoxyethylene-10-lauryl ether) surfactants, indicate that SPME is a viable method for estimating the micelle partition coefficients.

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.

Polycyclic aromatic hydrocarbons in smoke used to smoke cheese produced by the combustion of rock rose (Cistus monspeliensis) and tree heather (Erica arborea) wood.

In this work, the polycyclic aromatic hydrocarbons (PAHs) and their methyl derivatives concentrations have been determined in smoke from the rock rose and tree heather wood combustion. The combustion is done in two types of smokers, kiln and drum, commonly used in the Canary Islands (Spain) to smoke cheese. The low control of the operational conditions justify the great variability of the PAHs concentration in the emissions, with values between 251.8 and 2547 microg/m3N. In general, the lowest concentrations correspond to the tree heather wood combustion in the drum, while the highest concentrations are usually reached in the rock rose wood combustion in the kiln. However, the relative contributions of each PAH to the total concentration are independently similar to the type of smoker and wood used. In the combustion conditions, the equilibrium is not reached during the PAHs distribution process between the gas and aerosol phases. Therefore, while naphthalene and their 1- and 2-methyl derivatives remain in the gas phase, phenanthrene and PAHs with higher molecular weight remain mainly in the aerosol phase. In this phase, the PAHs concentration represents 39.9% of the total PAHs produced by burning rock rose wood and 29.1% of the total PAHs when tree heather wood is used. To establish the carcinogenic potential in both phases, the percentages of some PAHs were calculated. These values are significantly higher in the aerosol phase and, at the same time, higher when rock rose wood is used.

Solid-phase microextraction coupled to gas chromatography/mass spectrometry for determining polycyclic aromatic hydrocarbon-micelle partition coefficients.

Solid-phase microextraction (SPME) coupled to gas chromatography with MS detection has been employed to study the partition coefficients of PAHs to ionic and nonionic micelles. The results obtained in this work for seven PAHs, using 85-microm polyacrylate- and 100-microm poly(dimethylsiloxane)-coated fibers and anionic (sodium dodecyl sulfate), cationic (cetyltrimethylammonium bromide), and nonionic (polyoxyethylene-10-lauryl ether) surfactants, indicate that SPME is a viable method for estimating the partition coefficients of PAHs to micelle. The procedure could also be potentially extended to the measurement of partition coefficients between a wide variety of semi- or nonvolatile compounds and micellar media.

Solid-phase microextraction coupled with high-performance liquid chromatography for the analysis of heterocyclic aromatic amines.

Solid-phase microextraction (SPME) coupled with high-performance liquid chromatography (HPLC) with UV diode array detection (DAD) for the analysis of heterocyclic aromatic amines (HAs) is described. Four kinds of fiber coatings: Carbowax-templated resin (CW-TPR), Carbowax-divinylbenzene (CW-DVB), poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB) and polyacrylate (PA) were evaluated for extraction of nine most biologically active heterocyclic aromatic amines. Different parameters affecting to the microextraction and determination of HAs were studied, such as absorption and desorption time, desorption mode, composition of the solvent for desorption, pH, ionic strength, and percentage of methanol in the sample. To determine these amines in food samples a new simplified procedure is proposed, consisting of treatment of the sample with methanolic NaOH prior microextraction by CW-TPR fiber coating and HPLC-DAD determination. The advantages of this new method are the reduced amounts of time and organic solvents required.

Fast microwave-assisted dansylation of N-nitrosamines. Analysis by high-performance liquid chromatography with fluorescence detection.

A fast microwave-assisted dansylation procedure has been developed for the derivatization of N-nitrosamines prior to high-performance liquid chromatography determination. N-Nitrosomorpholine, N-nitrosodimethylamine, N-nitrosodiethylamine, N-nitrosopyrrolidine and N-nitrosopiperidine are first denitrosated by hydrobromic acid-acetic acid to produce secondary amines, which are then quantitatively dansylated in 5 min using radiation power of 378 W and a maximum pressure of 1.4 bar inside the reactor. The reaction mixture is separated on a C18 column with acetonitrile-water (55:45, v/v) as mobile phase with fluorimetric detection at 531 nm (excitation at 339 nm). The detection limits range from 8 to 75 pg for N-nitrosomorpholine and N-nitrosodiethylamine, respectively. The method was applied to study the recoveries of N-nitrosamines in beer and their determination in cigarette smoke.