Juan H. Ayala

Determination of polycyclic aromatic hydrocarbons in marine sediments by high-performance liquid chromatography after microwave-assisted extraction with micellar media

A simple and rapid method is developed for extraction and determination of polycyclic aromatic hydrocarbons (PAHs) in marine sediments. The procedure was based on the microwave-assisted extraction of PAHs in marine sediment samples using a micellar medium of Polyoxyethylene 10 lauryl ether as extractant. Two-level factorial designs have been used to optimize the microwave extraction process. The analysis of extracts has been carried out by HPLC with UV detection. Fortified sediments gave an average recovery between 85.70 and 100.73%, with a relative standard deviation of 1.77-7.0% for PAHs with a ring number higher than three.

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.

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

In this work, the nonionic surfactant polyoxyethylene-10-lauryl ether has been used for the extraction and preconcentration of 14 polycyclic aromatic hydrocarbons, classified as priority pollutants by the US Environmental Protection Agency, from seawater samples. The cloud-point preconcentration previous separation by HPLC and quantification using fluorimetric detection and wavelength programming allow to determine these pollutants with detection limits ranging from 1.0 to 1.5 x 10(2) ng/l with RSDs better than 10.4%. The methodology is evaluated using well-established extraction and preconcentration methods and GC-MS.

The metal-organic framework HKUST-1 as efficient sorbent in a vortex-assisted dispersive micro solid-phase extraction of parabens from environmental waters, cosmetic creams, and human urine.

Three metal-organic frameworks (MOFs), specifically HKUST-1, MOF-5, and MIL-53(Al), have been synthetized, characterized, studied and compared in a vortex-assisted dispersive micro-solid-phase extraction (VA-D-µ-SPE) procedure in combination with high-performance liquid chromatography (HPLC) with diode-array detection (DAD) for determining seven parabens in environmental waters (tap water, swimming pool water, and water coming from a spa pool), human urine (from two volunteers), and cosmetic creams (two commercial brands). Experimental parameters, such as nature and amount of MOF, sample volume, nature of elution solvent and its amount, vortex and centrifugation time, among others, were properly optimized. HKUST-1 was the most adequate MOF to work with. Detection limits for the overall method down to 0.1 μgL(-1) for butylparaben (BPB) and benzylparaben (BzPB) were obtained, with determination coefficients (R(2)) higher than 0.9966 for a range of 0.5-147 μgL(-1) (depending on the paraben), average relative recoveries (RR, in %) of 80.3% at the low spiked level (7 μgL(-1)), and relative standard deviation (RSD) values below 10% also at the low spiked level. The strength of the affinity between HKUST-1 and parabens was evaluated, and it ranged from 33.5% for isopropylparaben (iPPB) to 77.0% for isobutylparaben (iBPB). When analyzing complex environmental waters, RR values of 78%, inter-day precision values (as RSD) lower than 15%, and intra-day precision values lower than 7.8% were obtained, despite the observed matrix effect. When analyzing cosmetic creams, parabens were detected, with contents ranging from 0.14 ± 0.01 μgg(-1) for EPB in the healing cream analyzed to 1.12 ± 0.07 mgg(-1) for MPB in the mask cream analyzed, with precision values (RSD) lower than 12% and RR values from 63.7% for propylparaben (PPB) to 121% for iPPB. When analyzing human urine, no parabens were detected but the method could be performed with RSD values lower than 19%. These results show the adequateness of MOFs as sorbents in VA-D-µ-SPE procedures despite sample complexity.

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.

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-BF4) 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-BF4 were established and optimized. The method was applied for the determination of these compounds in commercial meat extracts.

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.

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 magnetic-based dispersive micro-solid-phase extraction method using the metal-organic framework HKUST-1 and ultra-high-performance liquid chromatography with fluorescence detection for determining polycyclic aromatic hydrocarbons in waters and fruit tea infusions.

A hybrid material composed by the metal-organic framework (MOF) HKUST-1 and Fe3O4 magnetic nanoparticles (MNPs) has been synthetized in a quite simple manner, characterized, and used in a magnetic-assisted dispersive micro-solid-phase extraction (M-d-μSPE) method in combination with ultra-high-performance liquid chromatography (UHPLC) and fluorescence detection (FD). The application was devoted to the determination of 8 heavy polycyclic aromatic hydrocarbons (PAHs) in different aqueous samples, specifically tap water, wastewaters, and fruit tea infusion samples. The overall M-d-μSPE-UHPLC-FD method was optimized and validated. The method is characterized by: its simplicity in both the preparation of the hybrid material (simple mixing) and the magnetic-assisted approach (∼10min extraction time), the use of low sorbent amounts (20mg of HKUST-1 and 5mg of Fe3O4 MNPs), and the low organic solvent consumption in the overall M-d-μSPE-UHPLC-FD method (1.5mL of acetonitrile in the M-d-μSPE method and 2.8mL of acetonitrile in the UHPLC-FD run). The resulting method has high sensitivity, with LODs down to 0.8ngL(-1); adequate intermediate precision, with relative standard deviation values (RSD) always lower than 6.3% (being the range 5.9-9.0% in tap water for a spiked level of 45ngL(-1), 6.1-14% in wastewaters for a spiked level of 45ngL(-1), and 7.2-17% in fruit tea infusion samples for a spiked level of 45ngL(-1)); and adequate relative recoveries, with average values of 82% in tap water, and 94% and 75% in wastewater and fruit tea infusion samples, respectively, if using the proper matrix-matched calibration.

Ultrasonic micellar extraction of polycyclic aromatic hydrocarbons from marine sediments

In this present study the extraction of polycyclic aromatic hydrocarbons (PAHs) from marine sediments with a micellar medium of Polyoxyethylene 10 lauryl ether by an ultrasound-assisted method has been studied. Factorial design experiments were used in order to optimize the extraction parameters: extraction time, surfactant concentration and surfactant volume:amount of sediment relationship. The results suggest that surfactant concentration is statistically the most significant factor. The analysis of extracts has been carried out by HPLC with UV detection. Fortified sediments gave an average recovery between 86.7 and 106.6%, with relative standard deviation of 2.02-6.83% for PAHs with a ring number higher than three.