Biomedical subjects

Soledad Cárdenas

Publications and source records attributed to Soledad Cárdenas.

10 recordsLinked to original sources

PubMed2006

Continuous flow configuration for total hydrocarbons index determination in soils by evaporative light scattering detection.

A continuous flow configuration is proposed for the estimation of the hydrocarbon index in soils using for the first time evaporative light scattering detection (ELSD). The method is based on a membrane-enrichment of the hydrocarbons of interest (C10-C40), which are previously extracted from the soil matrix with a water:hexane mixture using a household microwave oven. The organic supernatant is cleaned-up through silica, evaporated and redissolved in a sodium dodecyl sulphate aqueous solution which is introduced in the loop of an injection valve. The sample, carried by an aqueous stream, passes through a continuous filtration unit fitted with a 1 microm pore size PTFE membrane, where the hydrocarbons are retained while the potential coextracted compounds are wasted. Quantitative elution of the C10-C40 fraction is accomplished by passing an acetone stream through the filter which drives the analytes to the ELSD system for analytical measurement. The detection limit was 1.8 microg ml(-1), the linear range 5-25 microg ml(-1) and the precision 4.3%. The recoveries were between 93 and 97%. The proposed method was also evaluated by attenuated total reflexion-Fourier transform (ATR-FT-IR) analysis of the extracts.

Calibration↗

PubMed2006

Separation of carbon nanotubes in aqueous medium by capillary electrophoresis.

A robust and reproducible method for the dispersion of carbon nanotubes, either single-walled or multi-walled is presented. Dispersion of nanotubes was achieved as surfactant-coated species of sodium dodecyl sulphate. The addition of small amounts of hydroxypropyl methyl cellulose (HPMC) together with the surfactant, sodium dodecyl sulphate, was found critical to achieve reproducible nanotubes dispersion and to obtain an homogeneous and stable solution. This solution is further analyzed by capillary electrophoresis using a background electrolyte solution containing a polymer, 0.025% (w/v) HPMC solution prepared in 5 mM ammonium acetate at pH 8.03. This electrophoretic method presents a high reproducibility between runs, being an interesting alternative to study nanotube size distribution or characterization after synthesis. In addition, the methodology developed allowed the study of the interaction of the different types of carbon nanotubes with a molecular probe such as pentachlorophenol. This procedure was showed effective to detect small differences on the chemical/physical surface properties of the nanotubes. The different interaction behavior found within the two SWNTs selected was critically discussed.

Electrophoresis, Capillary↗

PubMed2005

Continuous autoanalyzer for the evaluation of the exhaustion of industrial degreasing baths based on the determination of total grease and surfactant contents.

A continuous flow autoanalyzer for at-line monitoring of total grease and surfactant contents in alkaline degreasing baths is proposed. For this purpose, a simple, robust, automated configuration has been on-line coupled to an universal response detector, such as the evaporative light scattering one. The proposed autoanalyzer constitutes an advantageous alternative to manual procedures and achieves the determination of both indices in ca. 15 min. The parameters thus obtained can be used to evaluate the degree of exhaustion of the bath as therefore allows the timely decision-making about reusability, maintenance or renewal. The fractionation model has been validated using attenuated total reflection-Fourier transform-infrared (ATR-FT-IR) spectroscopy. The potential of the method was realized by applying it to the analysis of 15 real samples obtained from precleaning and cleaning alkaline baths from a production line of a metal industry.

Industrial Waste↗

PubMed2005

ATR-FTIR membrane-based sensor for the simultaneous determination of surfactant and oil total indices in industrial degreasing baths.

Monitoring the exhaustion of alkaline degreasing baths is one of the main aspects in metal mechanizing industrial process control. The global level of surfactant, and mainly grease, can be used as ageing indicators. In this paper, an attenuated total reflection-Fourier transform infrared (ATR-FTIR) membrane-based sensor is presented for the determination of these parameters. The system is based on a micro-liquid-liquid extraction of the analytes through a polymeric membrane from the aqueous to the organic solvent layer which is in close contact with the internal reflection element and continuously monitored. Samples are automatically processed using a simple, robust sequential injection analysis (SIA) configuration, on-line coupled to the instrument. The global signal obtained for both families of compounds are processed via a multivariate calibration technique (partial least squares, PLS). Excellent correlation was obtained for the values given by the proposed method compared to those of the gravimetric reference one with very low error values for both calibration and validation.

Metallurgy↗

PubMed2005

ATR-FT-IR membrane-based sensor for integrated microliquid-liquid extraction and detection.

A novel straightforward membrane-based sensor, which uses attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy has been developed. The flow cell designed permits the on-line microliquid-liquid extraction of the target analyte into a organic solvent layer (OSL), which was deposited on the ATR surface using a sequential injection manifold. The aqueous and organic phases are separated via a commercial hydrophobic membrane placed on the PTFE piece of the cell. The main advantage of the proposed device is that the OSL can be created and regenerated in a continuous manner using the automatic manifold without opening the cell. The analytes are enriched into the OSL after diffusion through the membrane, which excludes the typical absorption bands of water. In addition, the behavior of different organic solvents was evaluated in order to increase the applicability and versatility of the proposed system. Finally, the analytical performance of the design was established for the detection and quantitation of Triton X100 in water.

Journal Article↗

PubMed2005

Autoanalyzer for continuous fractionation and quantitation of the polyphenols content in wines.

A simple continuous flow autoanalyzer for the on-line fractionation of the polyphenols content in wines is proposed. The target compounds are isolated from the matrix by solid-phase extraction on an RP-C18 sorbent column, using selective solvents for the sequential elution of each polyphenol family. Moreover, evaporative light scattering detection (ELSD) is used for the first time for the on-line monitorization of the three polyphenol fractions present in the wine samples. Thus, a single sample injection is required to determine the global concentration of the three selected polyphenol fractions and the whole analysis is completed within a few minutes. Three calibration graphs were constructed for quantitative analysis of the global compounds concentration in every fraction and covered the range 5-300 mg l(-1) (expressed as gallic acid). Average repeatability, expressed as relative standard deviation, was 4%. The proposed autonalyzer was applied to the analysis of a variety of commercial wine samples. The results obtained were compared with those provided by the Folin-Ciocalteau method, being similar in all instances.

Anthocyanins↗

PubMed2005

Present and future applications of carbon nanotubes to analytical science.

This article reviews the impact of carbon nanotubes on analytical science, and the main current and future applications of carbon nanotubes in this field. Given that it is necessary to solubilize carbon nanotubes for many applications, we consider the procedures developed to achieve this. The use of carbon nanotubes in analytical chemistry as a target analyte and as an analytical tool is also discussed. Chromatographic and electrophoretic methods used to separate and characterize carbon nanotubes are presented. The use of carbon nanotubes as an analytical tool in filters and membranes, as sorbent material for solid phase extraction, in electrochemical (bio)sensors, and in separation methods is discussed. It is clear that while nanotubes are being tested for use in many different fields, their truly enormous potential has yet to be realized in analytical chemistry.

Biosensing Techniques↗

PubMed2005

Direct olive oil authentication: detection of adulteration of olive oil with hazelnut oil by direct coupling of headspace and mass spectrometry, and multivariate regression techniques.

Control of adulteration of olive oil, together with authentication and contamination, is one of the main aspects in the quality control of olive oil. Adulteration with hazelnut oil is one of the most difficult to detect due to the similar composition of hazelnut and olive oils; both virgin olive oil and olive oil are subjected to that kind of adulteration. The main objective of this work was to develop an analytical method able to detect adulteration of virgin olive oils and olive oils with hazelnut oil by means of its analysis by a headspace autosampler directly coupled to a mass spectrometer used as detector (ChemSensor). As no chromatographic separation of the individual components of the samples exists, a global signal of the sample is obtained and employed for its characterization by means of chemometric techniques. Four different crude hazelnut oils from Turkey were employed for the development of the method. Multivariate regression techniques (partial least squares and principal components analysis) were applied to generate adequate regression models. Good values were obtained in both techniques for the parameters employed (standard errors of prediction (SEP) and prediction residual error sum of squares (PRESS)) to evaluate its goodness. With the proposed method, minimum adulteration levels of 7 and 15% can be detected in refined and virgin olive oils, respectively. Once validated, the method was applied to the detection of such adulteration in commercial olive oil and virgin olive oil samples.

Corylus↗

PubMed2003

Direct screening of lyophilised biological fluids for bile acids using an evaporative light scattering detector.

The usefulness of lyophilisation for the direct screening of biological fluids for bile acids was investigated. Human serum and urine were lyophilised without losses of the target compounds and further extracted with n-hexane in acidic medium under magnetic stirring. An integrated flow injection-liquid chromatographic system coupled to an evaporative light scattering detector (ELSD) was used for automated screening/confirmation. The continuous module allows sequential filtration of the organic phase, solvent changeover and solid-phase extraction for clean-up and preconcentration purposes. Retained bile acids were eluted with an acetonitrile-methanol (65:35, v/v) stream. For screening purposes, the effluent was directly introduced in the ELSD detector and the total bile acid content of the sample determined. For confirmatory analysis, another aliquot of the sample was processed in the screening module but the effluent was directed to the chromatographic columns, which provided the free bile acid profile of the sample. Fasting serum and urine samples obtained from healthy individuals were lyophilised and processed. Good agreement was obtained in the analysis of the two matrices assayed following the screening and confirmatory methods.

Bile Acids and Salts↗

PubMed2003

Autoanalyzer for milk quality control based on the lactose, fat, and total protein contents.

A novel autoanalyzer was developed to assess the quality of milk samples according to the percentage of lactose, fat, and total protein they contain. The module comprises two pumps (one of high pressure), an injection valve, a filter, and an evaporative light-scattering detector. A volume of 15 microL of dilute milk was injected in an ethanol-water (50% v/v) stream for precipitation/retention of protein/fat, being the lactose content determined in the filtrate. The fat fraction was calculated using an ethanol stream, and total protein was finally dissolved by means of a 1.7 mol/L acetic acid solution. The simplicity of the proposed automatic module lies in the universal response of the detector, which permits the determination of the three macrocomponents in milk. In addition, the flow injection method allows their sequential analysis in the same injected sample by using selective reagents for each compound. The proposed method was validated with an SRM milk sample as well as by comparison of the results obtained with those provided by the IR method. In addition, the proposed analyzer is cheaper than its counterpart that is based on infrared technique.

Animals↗