Biomedical subjects

R Cela

Publications and source records attributed to R Cela.

At least 37 records · Page 2Linked to original sources

PubMed2004

Further solid-phase microextraction-gas chromatography-mass spectrometry applications: "on-fibre" and aqueous photodegradation of nitro musks.

Photodegradation kinetics of four nitro musks (musk xylene, musk tibetene, musk ketone and musk moskene) in solid-phase microextraction (SPME) fibres ("photo-SPME") and in an aqueous system were studied by means of gas chromatography-mass spectrometry (MS) detection. Musks fragrances were extracted from aqueous solutions using SPME fibres that subsequently were exposed to different UV irradiation times, generating photoproducts easily characterized by their mass spectra. Aqueous photodegradation studies followed by SPME were also performed and compared to photo-SPME. The same fourteen photoproducts have been detected in both media. The potential of this approach to readily calculate apparent rate constants (from 10(-4) to 10(-3) s(-1)), half-life times (from 3 to 32 min) and reaction orders (n = 1) in both media is stated. The main photoreaction determined was photocyclization, but products of photoreduction and photorearrangement have also been detected. Tentative photodegradation pathways for musk moskene and musk tibetene are proposed for the first time.

Gas Chromatography-Mass Spectrometry↗

PubMed2004

Development of a solid-phase microextraction gas chromatography/tandem mass spectrometry method for polybrominated diphenyl ethers and polybrominated biphenyls in water samples.

Solid-phase microextraction has been applied for the first time to the determination of trace concentrations of some brominated flame-retardant compounds (BFRs) in water samples. For the development of the method, six polybrominated diphenyl ethers and two polybrominated biphenyls were considered as target analytes. The factors expected to influence the extraction process are fully discussed. Quantification has been performed by gas chromatography/tandem mass spectrometry using an ion trap mass analyzer. This is also the first time that tandem mass spectrometry is applied with these analytes. Unlike conventional methods for BFR analysis, which involve solvent extraction and several cleanup steps before gas chromatography, the proposed method uses headspace extraction and hard contamination of the chromatographic system is prevented. In addition, tandem mass spectrometry provides selectivity and sensitivity in the detection process. The method performs well achieving good linearity (R(2) > 0.997), precision, and detection limits (S/N = 3) ranging from 7.5 to 190 pg/L. The method has been applied to a variety of water samples.

Journal Article↗

PubMed2004

Solid-phase microextraction with on-fiber derivatization for the analysis of anti-inflammatory drugs in water samples.

A sensitive and solvent-free procedure for the determination of non-steroidal acidic anti-inflammatory drugs in water samples was optimized using solid-phase microextraction (SPME) followed by on-fiber silylation of the acidic compounds and gas chromatography-mass spectrometry (GC-MS) determination. Microextraction was carried out directly over the filtered water samples using a polyacrylate fiber. Derivatization was performed placing the SPME fiber, loaded with the extracted analytes, in the headspace of a vial containing 50 microl of N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA). Derivatives were desorbed for 3 min in the GC injector. Influence of several parameters in the efficiency of microextraction (volume of sample, time, pH, type of fiber coating, etc.) and derivatization steps (time, temperature and volume of MTBSTFA) was systematically investigated. In the optimal conditions an excellent linearity over three orders of magnitude and quantification limits at the ng/l level (from 12 to 40 ng/l) were achieved. The proposed method was applied to the determination of acidic compounds in sewage water and results compared to those obtained using solid-phase extraction (SPE) followed by the derivatization of the compounds in the organic extract of the solid-phase extraction cartridge.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2004

Determination of natural and synthetic estrogens in water by gas chromatography with mass spectrometric detection.

A procedure for the determination of six natural and synthetic estrogens (diethylstilbestrol, estrone, 17beta-estradiol, mestranol, 17alpha-ethinylestradiol and estriol) in water samples is described. Samples, up to 2000 ml, were concentrated using Oasis HLB solid-phase extraction cartridges. Analytes were derivatized with N-methyl-N-(trimethylsilyl)trifluoroacetamide and determined by GC-MS or GC-MS-MS. The reactivity of several silylation reagents versus aliphatic and aromatic hydroxyl groups contained in the structure of the selected analytes was evaluated. Influence of parameters such as sample pH, nature of the water samples and derivatization conditions on the performance of the whole analytical procedure was systematically studied. Under optimal conditions, quantification limits between 1 and 3 ng/l were achieved for the determination of the considered estrogens in sewage water.

Estrogens↗

PubMed2004

Applicability of solid-phase microextraction combined with gas chromatography atomic emission detection (GC-MIP AED) for the determination of butyltin compounds in sediment samples.

The performance of solid-phase microextraction (SPME) applied to the determination of butyltin compounds in sediment samples is systematically evaluated. Matrix effects and influence of blank signals on the detection limits of the method are studied in detail. The interval of linear response is also evaluated in order to assess the applicability of the method to sediments polluted with butyltin compounds over a large range of concentrations. Advantages and drawbacks of including an SPME step, instead of the classic liquid-liquid extraction of the derivatized analytes, in the determination of butyltin compounds in sediment samples are considered in terms of achieved detection limits and experimental effort. Analytes were extracted from the samples by sonication using glacial acetic acid. An aliquot of the centrifuged extract was placed on a vial where compounds were ethylated and concentrated on a PDMS fiber using the headspace mode. Determinations were carried out using GC-MIP AED.

Acetic Acid↗

PubMed2004

Chlorophenols identification in water using an electronic nose and ANNs (artificial neural networks) classification.

Electronic artificial noses are being developed as systems for the automated detection and classification of odours, vapors and gases. In the food industry, such devices are used as aids for quality control or process-monitoring tools. An electronic nose (EN) is generally composed of a chemical sensing system and a pattern recognition system (e.g. artificial neural network). An EN based on a non-specific conducting polymer array was used to monitor chlorophenols in water samples. Operational parameters for the EN were optimized by a Plackett-Burman factorial design. The experimental parameters studied were: sample volume, platen temperature, sample equilibration time, loop fill time, sample pressurization time and injection time. Optimal experimental conditions were applied to chlorophenols determination and differentiation in ultrapure water samples spiked with the EPA listed chlorophenols. Data analysis was carried out using principal component analysis (PCA) and artificial neural networks (ANNs) to predict the chlorophenols presence in water samples. The obtained results showed that it was possible to differentiate the five chlorophenol groups: monochlorophenol, dichlorophenol, trichlorophenol, tetrachlorophenol and pentachlorophenol. Differentiation of chlorophenol groups was based on Mahalanobis distance between the formed clusters. This Mahalanobis distance is designated by the Quality Factor, a value >2 for this quality factor means a good differentiation between the clusters.

Automation↗

PubMed2003

Simultaneous determination of neutral and acidic pharmaceuticals in wastewater by high-performance liquid chromatography-post-column photochemically induced fluorimetry.

An analytical method for the simultaneous determination of acidic and neutral pharmaceutical active compound (PhACs) residues in wastewater has been developed based on the combination of high-performance liquid chromatography (HPLC) and photochemically induced fluorimetry. The photoderivatization conditions for each particular PhAC have been assessed. Off-line optimization of the HPLC separation for both neutral and acidic compounds has been utilised and evaluated. Detection limits in the low ng/ml range have been achieved without sample pretreatment. By applying the developed analytical method combined with solid-phase extraction to real wastewater samples an enrichment factor of approximately two orders of magnitude can be obtained.

Chromatography, High Pressure Liquid↗

PubMed2003

Determination of acidic drugs in sewage water by gas chromatography-mass spectrometry as tert.-butyldimethylsilyl derivatives.

A procedure is described for the determination of five acidic non-steroidal anti-inflammatory pharmaceuticals (ibuprofen, naproxen, ketoprofen, tolfenamic acid and diclofenac) in sewage water. The analytical method involves the concentration of water samples using a solid-phase extraction polymeric sorbent, functionalized with N-vinylpyrrolidone. Analytes were eluted with ethyl acetate. derivatized using N-methyl-N-(tert.-butyldimethylsilyl)trifluoroacetamide (MTBSTFA) and analyzed by GC-MS. Influence of time, temperature and volume of MTBSTFA in the yield of the derivatization step were studied in detail using a factorial central composite design. Quantification limits of the analytical procedure for 500 ml of sewage water ranged from 20 to 50 ng/l. Recoveries from 90 to 115% were found for sewage water samples spiked with the studied compounds at the low ng/ml level. Results obtained for real samples show the presence of ibuprofen and naproxen in both influent and effluent of a sewage water treatment plant.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2002

Photolysis of polychlorinated biphenyls by solid-phase microextraction. "On-fibre" versus aqueous photodegradation.

The photodegradation kinetics of polychlorinated biphenyls "on-fibre" is described. The utilisation of solid-phase microextraction (SPME) fibres to monitor photolysis pathways and determine photoproducts constitutes a new approach that exploits the solvent-free aspect and concentration possibilities of this technique. Direct photolysis of aqueous solutions containing polychlorinated biphenyls (PCBs) was also undertaken and SPME was used in this case for photoproduct extraction purposes. Reductive dechlorination was the main decomposition mechanism in both procedures. Less-chlorinated biphenyls are the principal photoproducts and, among these, some toxic coplanar species have been detected. The influence of irradiation time was evaluated for both treatments. SPME was found to be a good choice for the extraction of photoproducts in experiments conducted in the classical way (extraction after photolysis). Moreover, it is demonstrated that photolysis of PCBs "on fibre" is realistic and provides the possibility of evaluating the phototransformation of these pollutants at environmental levels.

Mass Spectrometry↗

PubMed2002

Methylmercury determination in biological samples by derivatization, solid-phase microextraction and gas chromatography with microwave-induced plasma atomic emission spectrometry.

A method for the extraction and gas chromatographic determination of methylmercury in biological matrices is presented. By combining the advantages of two extraction techniques-microwave-assisted extraction (MAE) and solid-phase microextraction (SPME)--the separation of methylmercury from biological samples is possible. Specifically, the procedure involves microwave extraction with 3 M hydrochloric acid, followed by aqueous-phase derivatization with sodium tetraphenylborate and headspace SPME with a silica fibre coated with polydimethylsiloxane (PDMS). For optimization of the derivatization-SPME procedure, a central composite experimental design with alpha = 1.682 and two central points was used to model gas-chromatographic peak areas as functions of pH, extraction temperature and sorption time. A desirability function was then used for the simultaneous optimization for methylmercury and Hg(II). The optimal derivatization-SPME conditions identified were close to pH 5, temperature 100 degrees C, and sorption time 15 min. The identification and quantification of the extracted methylmercury is carried out by gas chromatography with microwave-induced plasma atomic emission spectrometry detection. The validity of the new procedure is shown by the results of analyses of certified reference materials.

Calibration↗

PubMed2002

On-fibre photodegradation studies of polychlorinated biphenyls using SPME-GC-MS-MS: a new approach.

The known advantages of solid-phase microextraction as a simple, one-step, rapid and solvent free extraction technique are exploited to study the photodegradation kinetics of polychlorinated biphenyls "on-fibre". The obtained results show the possibilities of this new approach not only to monitor the photolysis pathways of such compounds but to determine the photoproducts produced at different irradiation times and/or wavelengths. Photoproducts of PCB decomposition were less chlorinated biphenyls, among them some coplanar congeners have been found, which is important from a toxicological point of view.

Environmental Pollutants↗

PubMed2002

Strategically designed sample composition for fastest screening of polychlorinated biphenyl congeners in water samples.

A new strategy for preparing composite samples of special interest and applicability in environmental screening studies is presented. The use of supersaturated experimental design matrices to conduct the sample composition of water sample specimens in screening studies is demonstrated. In contrast to well known conventional sample composition, this strategic approach provides analytical objects allowing the accurate prediction of analyte concentration levels in the original individual sample specimens while fixing the number of experiments to be carried out down to the very number of sample specimens. This will be of special importance when dealing with analytes that require complicated, labour intensive and expensive analytical processes. To reach this goal, two main conditions must be fulfilled. The first one is the sparsity effect (Pareto principle) which holds for the specimens in the sampling campaign. This means that the number of really anomalous or contaminated specimens, as compared to the total number of specimens to be analysed, is low. In environmental screening studies, frequently this situation can be reasonably assumed. The second condition is to have an effective manner to develop and solve the experimental designs required to build-up the composite samples. The challenging problem of screening PCBs in water samples has been tackled to show the usefulness of this strategic approach by combining chemometrically assisted sample composition and rapid analysis using solid-phase microextraction of the composite samples.

Environmental Monitoring↗

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↗