Biomedical subjects

Rafael Lucena

Publications and source records attributed to Rafael Lucena.

6 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↗

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↗

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↗