Biomedical subjects

R Cela

Publications and source records attributed to R Cela.

13 recordsLinked to original sources

PubMed2001

Determination of polychlorinated biphenyls in milk samples by saponification-solid-phase microextraction.

A saponification-HSSPME procedure has been developed for the extraction of PCBs from milk samples. Saponification of the samples improves the PCB extraction efficiency and allows attaining lower background. A mixed-level fractional design has been used to optimize the sample preparation process. Five variables have been considered: extraction time, agitation, kind of microextraction fiber, concentration, and volume of NaOH aqueous solution. Also the kinetic of the process has been studied with the two fibers (100-microm PDMS and 65-microm PDMS-DVB) included in this study. Analyses were performed on a gas chromatograph equipped with an electron capture detector and a gas chromatograph coupled to a mass selective detector working in MS-MS mode. The proposed method is simple and rapid, and yields high sensitivity, with detection limits below 1 ng/mL, good linearity, and reproducibility. The method has been applied to liquid milk samples with different fat content covering the whole commercial range, and it has been validated with powdered milk certified reference material.

Animals↗

PubMed2001

Simultaneous determination of butyltin and phenyltin species in sediments using ultrasound-assisted leaching.

A fast and simple procedure is presented for the simultaneous leaching of butyl (mono, di and tributyl) and phenyl organotin species from sediment samples. Leached compounds are further ethylated with sodium tetraethylborate in aqueous medium, and analyzed by gas chromatography. After testing the stability of triphenyltin under different extraction conditions, ultrasound-assisted leaching at room temperature in the presence of acetic acid was been proposed as an extraction procedure compatible with the simultaneous determination of phenyl- and butyltin compounds in sediments. Recoveries between 70 and 90% were obtained for phenyl species in spiked samples prepared in the laboratory. Results for butyltin species were validated by use of the reference material PACS-2. Quantification limits, using GC-MIP-AES as measurement technique, were approximately 5-10 ng g(-1). Precision in the consecutive analysis of three sediment samples varied between 3 and 10%.

Chromatography, Gas↗

PubMed2000

Highly selective and efficient determination of US Environmental Protection Agency priority phenols employing solid-phase extraction and non-aqueous capillary electrophoresis.

Non-aqueous capillary electrophoresis has been used in the separation of a complete list of 26 priority phenols included in the 8041 US Environmental Protection Agency method and the 76/464/EEC European Union directive. A highly selective and efficient separation was obtained when the background electrolyte used was 150 mM ammonium acetate dissolved in N-methylformamide-acetonitrile (75:25). Solid-phase extraction was successfully assayed as an enrichment strategy for the analysis of low-concentration samples. A styrene-divinylbenzene functionalized cartridge provided excellent recoveries of phenols from water samples at neutral pH. The limits of quantification obtained permit the application of the proposed method to the determination of priority phenols in wastewater samples.

Electrophoresis, Capillary↗

PubMed2000

Optimisation of alachlor solid-phase microextraction from water samples using experimental design.

We have tested screening and response surface experimental designs to optimise the solid-phase microextraction (SPME) of the widely used herbicide alachlor. Extraction time and sample volume were the only statistically significant factors from those studied. In the final optimised conditions the procedure was applied to the SPME-HPLC analysis of alachlor in spiked water samples with excellent figures of merit.

Acetamides↗

PubMed2000

Solid-phase extraction of phenols.

Sample preparation for phenol analysis using solid-phase extraction (SPE) is reviewed. The scope of the review has been restricted to the literature dealing with the analysis of phenols as the main objective. The use, advantages and disadvantages of silica sorbents, polymeric, functionalized, carbon-based and mixed available sorbents, when applied to the separation and preconcentration of phenols, as well as the available experimental devices, are discussed. Other aspects such as phenol derivatisation prior to SPE, solid-phase microextraction, matrix effects and the storage of phenols in SPE cartridges, have been also discussed.

Chromatography, Liquid↗

PubMed2000

Analysis of barbiturates by micro-high-performance liquid chromatography with post-column photochemical derivatization.

This study attempts to combine the advantages of microcolumn high-performance liquid chromatography (micro-HPLC) with those of post-column photochemical derivatization in barbiturate analysis. Some barbiturates are photochemically unstable, leading to photoproducts that show maximum absorption at 270 nm and not the typical one at approximately 220 nm. For this purpose, a laboratory-built photoreactor has been developed to work with micro-HPLC instruments. Its performance is satisfactory in the forensic analysis of barbiturates.

Barbiturates↗

PubMed2000

Optimization of the extraction of polycyclic aromatic hydrocarbons from wood samples by the use of microwave energy.

A simple and rapid microwave-assisted extraction (MAE) procedure was developed and optimized for benzo[a]anthracene, benzo[e]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene and benzo[a]pyrene in wood samples. The spiked wood used was prepared 3 months before analysis to simulate weathering processes and to allow the formation of analyte-matrix interaction. The samples, immersed in acetonitrile were irradiated with microwaves in a closed-vessel system. Optimization of the method was achieved by using a factorial design approach on parameters such as extraction time, temperature and sample amount. The analysis of extracts has been carried out by reversed-phase high-performance liquid chromatography with fluorescence detection for quantification and UV-diode-array detection for confirmation. The MAE procedure yielded extracts that could be analyzed directly without any preliminary clean-up or solvent exchange steps.

Chromatography, High Pressure Liquid↗

PubMed1997

Evaluation of two solid-phase extraction procedures for the preconcentration of chlorophenols in drinking water.

Two off-line concentration procedures for the determination of sixteen chlorophenols in drinking water were developed. One involves acetylation of the samples and their subsequent preconcentration over graphitized carbon black cartridges. In the other, chlorophenols are derivatized following preconcentration over cross-linked styrene-divinylbenzene. The two proposed procedures are compared in terms of chlorophenol recoveries, throughput and breakthrough volume of the cartridges. The acetylated derivatives of chlorophenols are determined highly selectively at the concentration levels established by international legislation using gas chromatography in combination with microwave induced plasma atomic emission spectroscopy.

Chlorophenols↗

PubMed1997

Determination of phenolic pollutants in drinking water by capillary electrophoresis in the sample stacking mode.

A method for the determination of phenol, chlorophenols and nitrophenols at levels below those allowed by international legislation in water from the public supply is proposed. Ten of the compounds studied are included on the USA Environmental Protection Agency priority list of aquatic pollutants. Samples are concentrated off-line on cross-linked polystyrene and subsequently subjected to capillary electrophoresis using the sample stacking procedure to remove the matrix. The recoveries afforded by the off-line concentration process and the behaviour of the phenols in relation to sample stacking injection were examined.

Chlorophenols↗

PubMed1997

Speciation of organotin compounds in marine biomaterials after basic leaching in a non-focused microwave extractor equipped with pressurized vessels.

A rapid method for the speciation of butyl- and triphenyltin compounds in marine biotissues is described. A non-focused microwave extractor, operating at a power of 950 W and equipped with 12 pressurized vessels, was used to achieve fast sample leaching with tetramethylammonium hydroxide. The pH of the liquid extract was adjusted to 5. Organotins were ethylated with sodium tetraethylborate, extracted in isooctane and determined by means of a microwave-induced plasma atomic emission detector coupled to a gas chromatograph. The stability of butyl and phenyl compounds, exposed to the microwave energy, was studied as a function of the vessel temperature. The possibility of simultaneous carried-out extractions and the use of microwave to perform the ethylation and extraction of organotin compounds was also studied. The full procedure was validated with certified material NIES-11 and with real samples, by comparison with a classic leaching method using tetramethylammonium hydroxide without microwave.

Animals↗

PubMed1996

Determination of chlorophenols in drinking water with high resolution gas chromatography-tandem mass spectrometry.

A new method for the determination of sub-ppb levels of chlorophenols in drinking water by use of GC-MS-MS is proposed. Monitoring of these analytes for assurance of compliance with legally allowed limits can readily be accomplished by extraction as acetylated chlorophenols from low sample volumes (10 ml). Much lower detection limits can be achieved by preconcentrating 11 of sample using graphitized carbon cartridges for solid extraction. Appropriate selection of parent ions and fragmentation conditions ensures not only a high sensitivity, but also clean product ion spectra that allow positive identification of every species considered (polychlorophenol isomers included).

Calibration↗

PubMed1994

Determination of chlorophenols in drinking water samples at the subnanogram per millilitre level by gas chromatography with atomic emission detection.

The use of an atomic emission detector following a process of preconcentration of drinking water samples by a factor of 1500:1 allows the highly selective determination of chlorophenols present in samples below the maximum limit of 0.5 ng/ml set by international regulations. The preconcentration of the samples is carried out using 0.25-g commercial graphitized carbon cartridges without the need for sample derivatization prior to solid-phase extraction.

Chlorophenols↗

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↗