Biomedical subjects

R Cela

Publications and source records attributed to R Cela.

At least 19 recordsLinked to original sources

PubMed2006

Microwave-assisted extraction of organophosphate flame retardants and plasticizers from indoor dust samples.

A procedure for the determination of eight organophosphate flame retardants and plasticizers in dust samples is presented. Microwave-assisted extraction and gas chromatography (GC) with nitrogen-phosphorus detection (NPD) were used for sample preparation and analytes quantification, respectively. Influence of different variables (type and volume of organic solvent, temperature, time, agitation, etc.) on the yield of the extraction step was evaluated. The most important factor was the type of solvent, with the highest efficiencies corresponding to acetone. Under final conditions 10 mL of this solvent were employed. The extraction was carried out at 130 degrees C and satisfactory yields, similar to those obtained with the Soxhlet technique, were achieved. Due to the high content of organic carbon in dust samples, primary acetone extracts had to be subjected to intensive clean-up. Dilution with ultrapure water followed by concentration on a reversed-phase sorbent and further purification using silica, allowed a significant reduction of co-extracted interferences. Application of the developed methodology to indoor dust from private houses showed important concentrations of several organophosphate esters. The highest levels, up to 19 microg/g, corresponded to tris(butoxyethyl) phosphate; moreover, average values of two chlorinated compounds, used as flame retardants and considered as the most concerning species in the group, exceeded the 1 microg/g level.

Acetates↗

PubMed2006

Multicriteria optimisation of a simultaneous supercritical fluid extraction and clean-up procedure for the determination of persistent organohalogenated pollutants in aquaculture samples.

A useful tool based on a single-step extraction and clean-up procedure for the determination of 15 organohalogenated pollutants (including brominated flame retardants) in aquaculture samples, using aluminium oxide basic and acidic silica gel in the supercritical extraction cell followed by gas chromatography with electron capture detection or mass spectrometry has been developed. This effective clean-up step ensures a minimum of chromatographic difficulties related to complex matrix components such as aquaculture feed. The extraction procedure has been screened by a fractional factorial design for the preliminary statistically significant parameters. The factors selected were extraction temperature, pressure, static extraction time, dynamic extraction time and carbon dioxide flow rate. The Doehlert design, followed by a multicriteria decision-making strategy, was then performed in order to determine the optimum conditions for the two most significant factors: pressure (165 bar) and dynamic extraction time (27 min). Under optimal conditions, the procedure developed with GC-MS/MS provides an excellent linearity, detection (0.01-0.2 ng g(-1)) and quantification limits (0.05-0.8 ng g(-1)) for most of the analytes investigated. The feasibility of the proposed supercritical fluid extraction method was validated by analysing two reference materials and fish feed and shellfish samples with satisfactory results.

Animal Feed↗

PubMed2006

Computer-assisted transfer of programmed elutions in reversed-phase high-performance liquid chromatography.

Computer-assisted procedures were used to simulate modifications in chromatograms caused by the transfer of elution programmes between instruments with significantly different dwell volumes. Moreover, for the first time the same approach was used to modify the elution programmes to match the chromatograms produced in the different instruments. The process may consist of making minor modifications to gradient programmes or transforming the original gradient programme into a stepwise gradient profile and/or the simultaneous programming of flow and solvent composition. The combination of these approaches has been shown to have an enormous potential for producing matched chromatograms in instrumental systems with dwell volumes that differ by several millilitres. The efficiency and robustness of the proposed procedure is demonstrated with a variety of compounds (two different mixtures of 10 and 11 analytes), mobile phases (methanol and acetonitrile gradients), flow rates (0.5-1.5 mL/min range), temperatures (35-45 degrees C interval) and gradient profiles (linear, multilinear, curved and stepwise).

Acetonitriles↗

PubMed2006

Rapid screening of polychlorinated biphenyls in sediments using non-equilibrium solid-phase microextraction and fast gas chromatography with electron-capture detection.

A rapid method for the screening of polychlorinated biphenyls (PCBs) in sediment samples is described. Analytes are concentrated on a poly(dimethylsiloxane) (PDMS) solid-phase microextraction (SPME) fibre, separated using a narrow-bore gas chromatography column (10 m x 0.1mm I.D.) and determined with a micro-electron-capture detector (micro-ECD). The narrow-bore column showed a similar separation efficiency to a conventional capillary one (30 m x 0.32 mm I.D.) and allowed a 3 times reduction in the analysis time. Moreover, thermal desorption of SPME fibres in the narrow-bore column did not produce any degradation in the quality of separations when compared to the split injection mode. The use of an oxidative sample treatment was mandatory to remove sulphur interferences in the chromatograms and increase the yield of PCBs during SPME for short sampling times. Under optimised conditions, a fraction of sediment (0.1-0.5 g) was mixed with 5 ml of a 0.2M potassium permanganate solution and 0.5 ml of sulphuric acid 6M in a 22 ml closed vessel. Sample treatment and headspace SPME of PCBs were performed simultaneously for 10 min at 100 degrees C. Globally, the whole analytical procedure takes about 20 min and presents quantification limits between 0.5 and 1.3 ng/g. Accuracy was evaluated by analysing a reference sediment sample with certified concentrations of several PCBs.

Chromatography, Gas↗

PubMed2006

Optimization of a microwave-assisted extraction method for the analysis of polycyclic aromatic hydrocarbons from fish samples.

A microwave-assisted extraction (MAE) procedure has been developed and optimized for the extraction of six regulated polycyclic aromatic hydrocarbons (PAHs) from muscle samples of polluted fish. The procedure involves the simultaneous microwave-assisted extraction of PAHs with n-hexane and the lipids hydrolysis with potassium hydroxide. Experimental design methodology allows a quick and robust optimization of operational parameters such as the extraction time, temperature, and solvent volumes. In these final optimized conditions, the procedure can be applied to a vast range of fat containing fish samples without significant changes, thus enabling its routine use. Recoveries around 90% for the studied compounds benz[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene, and indene[1,2,3-cd]pyrene and quantification limits (between 0.07 and 0.53 ng/g dry weight) far below the regulated limits, have been obtained. The procedure is applied to several different fish samples. Further, accuracy validation using NIST SRM 2977 reference material was carried out.

Animals↗

PubMed2006

Approaches for the simultaneous extraction of tetrabromobisphenol A, tetrachlorobisphenol A, and related phenolic compounds from sewage sludge and sediment samples based on matrix solid-phase dispersion.

A procedure based on matrix solid-phase dispersion (MSPD) for sample preparation in the analysis of some bromophenols and halogenated bisphenols in sediments and sludges has been developed. For the first time ever, MSPD was applied for the extraction of organic contaminants from sediment and sewage sludge samples. The influence of experimental conditions on the yield of the extraction process and on the efficiency of the built-in cleanup step was thoroughly evaluated. Analysis of the extracts was performed by nonaqueous capillary electrophoresis coupled with photodiode array ultraviolet detection, using large-volume sample stacking injection based on the electroosmotic flow pump as an on-column preconcentration technique. The method was applied to the analysis of real sludges from urban sewage treatment plants, as well as river and marine sediment samples.

Journal Article↗

PubMed2006

Optimisation of a solid-phase microextraction method for the determination of parabens in water samples at the low ng per litre level.

A procedure for the determination of five esters of p-hydroxybenzoic acid (parabens) in water samples is presented. Analytes (methyl, ethyl, propyl, butyl and benzyl paraben) are concentrated on a solid-phase microextraction (SPME) fibre, converted on their tert-butyldimethylsilyl derivatives and selectively determined using gas chromatography in combination with tandem mass spectrometry (GC-MS/MS). Influence of different factors on the efficiency of extraction and on-fibre derivatization steps is described in detail. For all species, the highest enrichment factors were achieved using a polyacrylate (PA) fibre exposed directly to stirred water samples, containing 150 mg/ml of sodium chloride, at room temperature. Performance of the further on-fibre derivatization reaction was also maximum at room temperature, considering a short exposition period of the SPME fibre to vapours of the silylation reagent. Under optimised conditions, the proposed method achieved quantification limits from 0.001 to 0.025 ng/ml and it was free of matrix effects; therefore, external calibration can be used as the quantification technique. From our knowledge, this work describes the first application of SPME and gas chromatography to the determination of parabens in water. The analysis of a limited number of real samples revealed the presence of parabens in raw sewage water at concentrations up to 3 ng/ml.

Calibration↗

PubMed2006

Suitability of solid-phase microextraction for the determination of organophosphate flame retardants and plasticizers in water samples.

The feasibility of solid-phase microextraction (SPME) for the determination of several organophosphorus flame retardants and plastizicers in water samples by gas chromatography-nitrogen phosphorous detection (GC-NPD) is evaluated. These compounds have a wide range of polarities and volatilities and require a thorough optimisation of the different SPME parameters. Considering also possible contamination and carryover sources, the best compromise microextraction conditions were found to be direct extraction of 22 ml samples, containing 300 mg/ml of NaCl, with a PDMS-DVB coated fibre at room temperature. Although equilibrium was not achieved, an extraction time of 40 min allowed obtaining a good sensitivity (quantification limits between 0.010 and 0.025 ng/ml), comparable to that achieved by solid-phase extraction (SPE) of 1l samples, producing both similar values of precision and accuracy. Furthermore, the SPME method has shown to be free of matrix effects, avoiding the need of employing the standard addition procedure for quantification, and was suitable for the determination of eight of the nine considered compounds. Only tris-(2-ethylhexyl)-phosphate was neither determinable by SPME nor by SPE. Finally, the application of the developed methodology to the analysis of wastewater samples, showed that important concentrations of these compounds (up to 10 ng/ml) have been detected in treated sewage water, being discharged into the aquatic environment.

Chromatography, Gas↗

PubMed2005

Aquatic degradation of triclosan and formation of toxic chlorophenols in presence of low concentrations of free chlorine.

The degradation of 2-(2,4-dichlorophenoxy)-5-chlorophenol (triclosan) in chlorinated water samples was investigated. Sensitive determination of the parent compound and its transformation products was achieved by gas chromatography with mass spectrometry detection after sample concentration, using a solid-phase extraction sorbent and silylation of the target compounds. Experiments were accomplished using ultrapure water spiked with chlorine and triclosan concentrations in the low mg/l and ng/ml ranges respectively. Chlorination of the phenolic ring and cleavage of the ether bond were identified as the main triclosan degradation pathways. Both processes led to the production of two tetra- and a penta-chlorinated hydroxylated diphenyl ether, as well as 2,4-dichlorophenol. The formation of 2,3,4-trichlorophenol was not detected in any experiment; however, significant amounts of 2,4,6-trichlorophenol were noticed. All of these five compounds were also identified when triclosan was added to tap-water samples with free chlorine concentrations below 1 mg/l. Minor amounts of three di-hydroxylated phenols, containing from one to three atoms of chlorine in their structures, were also identified as unstable triclosan chlorination by-products. The analysis of several raw wastewater samples showed the co-existence of important concentrations of triclosan and its most stable by-products (2,4-dichlorophenol and 2,4,6-trichlorophenol), reinforcing the potential occurrence of the described transformations when products containing triclosan are mixed with chlorinated tap water.

Chlorine↗

PubMed2005

Microwave assisted extraction followed by gas chromatography with tandem mass spectrometry for the determination of triclosan and two related chlorophenols in sludge and sediments.

A procedure for the determination of 2-(2,4-dichlorophenoxy)-5-chlorophenol (Triclosan) and two possible transformation compounds, 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP), in sludge from sewage treatment plants (STP) and sediments is presented. Extraction was performed using an acetone:methanol (1:1) mixture under the action of a microwave field. The centrifuged supernatant was diluted with a NaOH aqueous solution and twice extracted with n-hexane for removing neutral and basic interferences. The aqueous layer was acidified and processed as a waste water sample. After concentration analytes were silylated and determined by gas chromatography with tandem mass spectrometry (GC-MS/MS). Influence of experimental conditions on the yield of the extraction process and on the efficiency of the further clean-up step was thoroughly evaluated. Performance of MS/MS detection in comparison to single MS is described. Under final working conditions quantification limits between 0.4 and 0.8 ng/g and recoveries from 78% to 106% were obtained. The method was applied to the analysis of several sludge and sediment samples. Only low levels of TCS were detected in some of the sediments; however, all three compounds were found in sludge samples at concentrations ranging from 7 to 316 ng/g, in the case of chlorophenols, and from 420 to 5400 ng/g, for Triclosan.

Chemical Fractionation↗

PubMed2005

Application of matrix solid-phase dispersion in the analysis of priority polycyclic aromatic hydrocarbons in fish samples.

The performance of matrix solid-phase dispersion (MSPD) for the extraction of polycyclic aromatic hydrocarbons (PAHs) in fish tissue is described. The suitability of different solid supports was tested as well as the influence on the extraction efficiency of the natural fat content in samples. Under optimal conditions 0.6-0.8 g of tissue sample, are dispersed with 2 g of octadecylsiloxane (C18) and 0.5 g of anhydrous sodium sulphate and transferred to the top of a polyethylene solid-phase extraction cartridge which already contains 2 g of florisil and 1 g of C18. Cartridges were eluted with acetonitrile. The analysis of the extracts was carried out by high-performance liquid chromatography (HPLC) coupled with fluorescence detection. The proposed method provides detection limits between 0.04 and 0.32 ng/g for the different considered PAHs, below the maximum levels established by the some regulatory bodies for the six PAHs after recent oil spill episodes and European Union regulations. Recoveries over 80% were obtained for all compounds. Accuracy validation was carried out using the US National Institute of Standards and Technology (NIST) SRM 2977 reference material.

Animals↗

PubMed2005

Optimization of solid-phase microextraction conditions for the determination of triclosan and possible related compounds in water samples.

A solid-phase microextraction (SPME) method for the determination of triclosan, methyl triclosan, 2,4-dichlorophenol and 2,3,4-trichlorophenol (considered as possible triclosan metabolites) in water samples was optimised. Analytes were first concentrated on a SPME fibre, directly exposed to the sample, and then triclosan and the two chlorinated phenols on-fibre silylated using N-methyl-N-(tert.-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA). Methyl triclosan remained unaffected during the derivatization step. Compounds were determined using gas chromatography in combination with mass spectrometry (GC-MS). Influence of different factors on the efficiency of extraction and derivatization steps was systematically investigated. Using a polyacrylate (PA) fibre quantification limits below 10 ng/l, and acceptable relative standard deviations, were obtained for all compounds after an extraction time of 30 min. On-fibre silylation was carried out in only 10 min. Moreover, the efficiency of the procedure was scarcely affected by the type of water sample. The method was applied to several samples of treated and raw wastewater, triclosan was found in all samples, at concentrations from 120 to 14,000 ng/l, and 2,4-dichlorophenol in most of them, at levels up to 2222 ng/l.

Acetamides↗

PubMed2005

Analysis of tetrabromobisphenol A and other phenolic compounds in water samples by non-aqueous capillary electrophoresis coupled to photodiode array ultraviolet detection.

Non-aqueous capillary electrophoresis (NACE) with large-volume sample stacking injection using the electroosmotic flow pump (LVSEP) has been developed for the determination of tetrabromobisphenol A (TBBPA) and other phenolic compounds in environmental matrices. Methanol has been used as run buffer solvent to reduce the electroosmotic flow (EOF). Identification and quantification of the analytes was performed by photodiode array ultraviolet detection. LVSEP-NACE improved sensitivity of the peak height by 90-300-fold. The method developed was applied to the analysis of TBBPA in river water and wastewater samples, using solid-phase extraction (SPE) as sample pretreatment process. The average recoveries of the analytes were in the range of 96-106% and 73-103% for 1 L of river water and 0.5 L of wastewater samples, respectively. When the method was based on off line SPE-LVSEP-NACE, sensitivity was improved by 3300-4500-fold and 1600-2200-fold for river water and wastewater samples, respectively.

Electrophoresis, Capillary↗

PubMed2005

Multi-residue screening of chlorinated and brominated compounds from aquaculture samples using matrix solid-phase dispersion--gas chromatography-mass spectrometry.

An effective multiresidual method for the trace analysis of fifteen compounds from a diverse group of pesticides, polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyl (PCBs) and polybrominated biphenyl (PBBs) in aquaculture feed is described. The analytical procedure is based on the matrix solid-phase dispersion (MSPD) of feed sample and subsequent elution with hexane. The MSPD process was evaluated using an asymmetrical experimental design 2(3)3(2)//9. Factors such as C18 sorbent amount, kind of adsorbents, solvent volume and elution mode were considered. The results suggest that the operational MSPD conditions are elution with pressure, 1 g of C18, basic alumina as adsorbent and 30 mL of hexane. The overall method including MSPD procedure and GC coupled to mass spectrometry (MS/MS) has been applied to several samples of aquaculture feed and marine species. Precision and accuracy of the analytical method were determined using the reference material from the International Atomic Energy Agency (IAEA-406), showing a good agreement to the referenced values.

Aquaculture↗

PubMed2005

Comparative study of aqueous and non-aqueous capillary electrophoresis in the separation of halogenated phenolic and bisphenolic compounds in water samples.

Capillary zone electrophoresis methods, based on either aqueous and non-aqueous solutions as running buffers and UV spectrophotometric detection, have been developed and optimized for the separation of several halogenated phenolic and bisphenolic compounds, suspected or proved to exhibit hormonal disrupting effects. Both aqueous capillary electrophoresis (CE) and non-aqueous capillary electrophoresis (NACE) methods were suitable for the analysis of compounds under study. The separation of the analytes from other 25 potentially interfering phenolic derivatives was achieved with NACE method. Large-volume sample stacking using the electroosmotic flow pump (LVSEP) was assayed as on-column preconcentration technique for sensitivity enhancement. LVSEP-CE and LVSEP-NACE improved peak heights by 5-26 and 16-330 folds, respectively. To evaluate their applicability, the capillary electrophoresis methods developed were applied to the analysis of water samples, using solid-phase extraction as sample pre-treatment process.

Electrophoresis, Capillary↗

PubMed2005

Photochemical studies of a polybrominated diphenyl ethers (PBDES) technical mixture by solid phase microextraction (SPME).

In this work the photochemical behaviour of a technical mixture of polybrominated diphenyl ethers (PBDEs) (BDE-47, BDE-99, BDE-100, BDE-153 and BDE-154) has been studied. The mixture of BDEs was extracted from aqueous solutions using SPME fibers that were subsequently exposed to different UV irradiation times, procedure so-called Photo-SPME. PBDEs photochemical studies in such medium have been accomplished for the first time. Twenty one different photoproducts, all of them generated by successive bromine atoms losses, have been identified, being their photoformation-photodegradation curves easily determined by the Photo-SPME technique.

Bromine↗

PubMed2004

Strategic sample composition in the screening of polycyclic aromatic hydrocarbons in drinking water samples using liquid chromatography with fluorimetric detection.

The screening of polycyclic aromatic hydrocarbons in water samples by means of the strategic sample composition (SSC) technique is presented. SSC uses special supersaturated composition matrices to perform sample composition and analysed the results obtained in the analytical determination of these composite samples by means of evolutionary assisted regression procedures providing estimations of the concentration levels of analytes in each individual sample specimen. Here, 12 composite samples were prepared by departing from 26 water sample specimens, five of which were spiked with known amounts of several polycyclic aromatic hydrocarbons (PAHs). These composite samples were analysed by HPLC using fluorescence detection. Concentration levels spiked were, in some cases clearly higher than allowed limits for drinking waters, whereas in other cases are just in the limit or even down these limits. The study shows the ability of SSC to detect the really contaminated samples and guiding the analyst in taking the adequate decisions.

Chromatography, High Pressure Liquid↗

PubMed2004

Applicability of solid-phase microextraction followed by on-fiber silylation for the determination of estrogens in water samples by gas chromatography-tandem mass spectrometry.

A solvent-free method for the determination of five estrogens in water samples at the low ng/l was optimized. Compounds were first concentrated on a polyacrylate (PA) solid-phase microextraction (SPME) fiber, directly exposed to the water sample, and then on-fiber silylated on the headspace of a vial containing 50 microl of N-methyl-N-(trimethylsilyl) trifluoroacetamide (MSTFA). Derivatized analytes were determined using GC with MS/MS detection. Influence of several factors on the efficiency of the microextraction step (e.g. time, sample volume, pH, ionic strength and fiber coating) is systematically described. Derivatization conditions were optimized in order to achieve the complete silylation of all hydroxyl groups contained in the structure of the compounds. Detection limits (from 0.2 to 3 ng/l) are compared with those obtained using the same detection technique and different sample preparation strategies, such as solid-phase extraction followed by silylation of the analytes in the organic extract and SPME without derivatization. The method was applied to the analysis of sewage water samples. Two of the investigated species were detected above the quantification limits of the procedure.

Estrogens↗