Biomedical subjects

E Rubí

Publications and source records attributed to E Rubí.

8 recordsLinked to original sources

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

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

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

Development of a matrix solid-phase dispersion method for the screening of polybrominated diphenyl ethers and polychlorinated biphenyls in biota samples using gas chromatography with electron-capture detection.

A low cost method for the screening of six polybrominated diphenyl ethers (PBDEs) and seven polychlorinated biphenyls (PCBs) in biological samples containing up to 100% of fat is presented. Compounds are extracted from the sample and isolated from lipids using a matrix solid-phase dispersion (MSPD) cartridge and 20 ml of n-hexane as elution solvent. PBDEs and PCBs are fractionated on a second cartridge containing 2 g of a normal phase sorbent. The potential of neutral silica, Florisil and basic alumina to separate PBDEs and PCBs in two independent fractions has been evaluated. The best results were obtained using silica. PCBs are eluted, in a first fraction, using n-hexane. PBDEs are further recovered with n-hexane-dichloromethane. The applicability of the method for the screening of PBDEs and PCBs, in samples containing both groups of compounds, has been demonstrated using spiked, certified and real polluted samples from different biota materials. Globally, recoveries higher than 75% and quantification limits around 0.4 ng/g have been achieved using gas chromatography with electron-capture detection (GC-ECD).

Animals↗

PubMedDate not supplied

Selective determination of methyl mercury in biological samples by means of programmed temperature gas chromatography.

A programmed temperature gas chromatographic method is presented by which it is possible to carry out routine analysis of methyl mercury in biological samples prepared according to the AOAC official first action recommendations without the need for preliminary treatment of the columns. This method greatly extends the life of the columns as well as the useful time for analysis; it has good linearity and repeatability. With the proposed method a total of 36 samples can be analyzed daily.

Animals↗