Biomedical subjects

M D Luque De Castro

Publications and source records attributed to M D Luque De Castro.

6 recordsLinked to original sources

PubMed2004

Fully automated method for the determination of 24,25(OH)2 and 25(OH) D3 hydroxyvitamins, and vitamins A and E in human serum by HPLC.

A new fully automated method for the determination of metabolites of Vitamin D(3) and Vitamins A and E has been developed. A robotic station for liquid-liquid extraction, connected on line with an automatic system for solid-phase extraction (Prospekt) and a liquid chromatograph were used and the complexity of the overall method was overcome by full automation. The eluate from the chromatograph was monitored by a photodiode-array detector at three wavelengths, namely, 265 nm for Vitamin D(3) metabolites, 291 nm for Vitamin E and 325 nm for Vitamin A-which are the maximum absorption wavelengths for the analytes. The time required per sample analysis was 35 min because of the overlapping development of the steps. The linearity obtained for serum samples (standard addition method) gives correlation coefficients (r(2)) ranging between 0.996 and 0.989, with standard deviation of the slope between 4.0 and 4.9%. The repeatability was between 4.0 and 6.0% and the within-laboratory reproducibility was lower than 10.1% in all cases-both expressed as relative standard deviation-for low concentrations of the analytes, namely, 3 ng/ml for 24,25(OH)(2) dihydroxyvitamin D(3), 10 ng/ml for 25(OH) hydroxyvitamin D(3), 100 ng/ml for Vitamin A and 2 microg/ml for Vitamin E. The method has been validated using a CRM (NIST, SRM968c).

24,25-Dihydroxyvitamin D 3↗

PubMed2004

Automated method for the determination of fat-soluble vitamins in serum.

A new fully automated high-performance liquid chromatography (HPLC) method using 1 ml of serum has been developed for the determination of retinol (Vitamin A), alpha-tocopherol (Vitamin E), 25-hydroxyvitamin D(3) and 24 R,25-hydroxyvitamin D(3). The eluate was monitored with a photodiode-array detector at three wavelengths-namely: 265 nm for Vitamin D(3), 291 nm for Vitamin E and 325 nm for Vitamin A. The detection limits were equal to or lower than 1 ng ml(-1) for all vitamins. The linearity obtained with serum samples (standard addition method) gives correlation coefficients (r(2)) ranging between 0.999 and 0.996 in all cases, with standard deviation of the slope between 3.2 and 1.6%. The repeatability was between 4.0 and 6.0% and the within-laboratory reproducibility was lower than 10% in all cases. The most outstanding features of the present method are its ease of use, its rapidity and fully automation, which enables its use for routine analysis. The time required per sample was 30 min, because the overlapped development of the steps. This method was used for the determination of normality range of these vitamins in healthy people in the 18-80-year-old interval.

Automation↗

PubMed2003

Slurry sampling-microwave assisted leaching prior to hydride generation-pervaporation-atomic fluorescence detection for the determination of extractable arsenic in soil.

A flow injection-pervaporation method, where the sample was introduced as slurry, has been developed for the continuous derivatization and determination of arsenic in soil by hydride generation-atomic fluorescence spectrometry. The removal of arsenic is achieved with the help of a microwave digestor, which facilitates an on-line leaching in the flow injection manifold. Slurries, prepared by mixing the soil (particle size <65 microm) with 6 mol L(-)(1) HCl, were magnetically stirred for 3 min, and while stirring, the pump aspirated the aliquot and filled the loop (500 microL) of the injection valve. An industrial soil and five types of soil (sandy, clayey, slimy, limy, organic) were selected for the optimization of the leaching and determination steps of arsenic, respectively. The results obtained from three certified reference materials [stream sediment GBW 07311 (188 microg/mL As), river sediment CRM 320 (76.7 microg/mL As), and soil GBW 07405 (412 microg/mL As)] using direct calibration against aqueous standards demonstrate the reliability of the method. The relative standard deviation for within-laboratory reproducibility was 4.5%.

Journal Article↗

PubMed2002

Sequential spectrophotometric determination of methanol and iron in vinegar by a flow injection-pervaporation method.

An easily automatable sequential flow-injection-pervaporation method is proposed for the photometric determination of methanol and iron in vinegar. The method is based on separation of the methanol from the sample matrix by pervaporation followed by its oxidation to formaldehyde with permanganate, decolouration of the latter with S(2)O(5)(2-), and subsequent reaction of formaldehyde with p-rosaniline to yield a violet reaction product with maximum absorption at 567 nm. Iron is determined by an existing method based on reaction with thiocyanate in acidic medium and monitoring at 508 nm. After optimisation by either the univariate or multivariate approaches, as required, the linear range was established for methanol (4-1000 mg L(-1)) and iron (0.18-20 mg L(-1)). The proposed method was then compared with reference methods for methanol and iron in terms of repeatability (2.452 mg L(-1) and 0.245 mg L(-1), respectively), reproducibility (4.435 mg L(-1) and 0.356 mg L(-1), respectively), detection limit (LOD=82 and 0.234 mg L(-1), respectively), and traceability. The throughput was nine samples per hour.

Acetic Acid↗

PubMed2000

On-line detection for supercritical-fluid extraction.

An overview of the direct coupling of supercritical-fluid extraction (SFE) to distinct detection is presented. The versatile construction of this kind of hybrid analytical instrumentation is manifested through the discussion of several interface prototypes, whose characteristics satisfy the requirements of both the SF extractor and detector. The application of several experimental strategies during the whole analytical process are proposed for the successful quantification of the leaching yield. Typical examples of SFE with on-line detection in several fields of analysis are presented, considering of special interest the information provided by the molecular and atomic techniques used. Finally, the real analytical capabilities of the automation of sample handling by SFE-continuous detection are also discussed.

Chromatography↗

PubMed1999

Accelerated extraction of the fat content in cheese using a focused microwave-assisted soxhlet device.

A fast method for hydrolysis and extraction of fat in cheese based on the use of a Soxhlet extractor assisted by microwaves is proposed. The use of this type of energy dramatically reduces the time required for both steps (namely, the hydrolysis time was decreased from 1 h to 10 min with avoidance of the neutralization step, and the extraction time was decreased from 6 h to 40 min), providing similar efficiency and reproducibility comparable to or better than that of the conventional Soxhlet methodology. In addition, the proposed method is cleaner than conventional Soxhlet, as 80-85% of the extractant is recycled. The determination of the fatty acid composition by gas-liquid chromatography and quantification of both polymer formation by high-performance size exclusion liquid chromatography and nonpolar triacylglycerol formation by thin-layer chromatography with flame ionization detection in the extracts obtained by the proposed method, conventional Soxhlet and Weibull-Berntrop procedures (Soxhlet with a prior hydrolysis step), showed that the quality of the extracts obtained by the proposed procedure is better than that of the conventional alternatives, possibly due to the shorter time required by the accelerated method.

Cheese↗