Biomedical subjects

R Cela

Publications and source records attributed to R Cela.

43 records · Page 3Linked to original sources

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↗