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Biomedical subjects

J M Leão

Publications and source records attributed to J M Leão.

4 recordsLinked to original sources

Further improvements in the application of high-performance liquid chromatography, capillary electrophoresis and capillary electrochromatography to the analysis of algal toxins in the aquatic environment.

The presence of algal toxins in the aquatic environment represents an important socioeconomic concern in many places worldwide, due to the toxicity that these compounds can induce in seafood or freshwater organisms at very low levels. Several analytical alternatives have been proposed over the last years for the control of these contaminants, which acute or chronic toxicity requires low detection levels and demands for the search of sensitive methods for their detection and determination. HPLC has been widely used for this purpose, although several alternatives such as CE or capillary electrochromatography (CEC) are being lately developed with this aim. In this work we report on the application of improved HPLC, as well as CE and CEC, for the analysis of diarrhetic shellfish poisoning toxins, amnesic shellfish poisoning (ASP) toxins and microcystins (MCs) present in different matrices such as water, shellfish or algae. Improvements in sample preparation for increasing sensitivity and selectivity are also shown. While UV and fluorimetric detection are the detection methods generally used, mass spectrometric detection was also applied for ASP toxins and MCs, especially for confirmatory purposes. From the results obtained it can be concluded that both HPLC and CE offer a good potential for a sensitive and selective determination of these algal toxins in such complex matrices. The results obtained for CEC allow also to conclude that this technique can result in a promising technique for such application.

Chromatography, High Pressure Liquid↗

Capillary electrophoresis with diode array detection as an alternative analytical method for paralytic and amnesic shellfish toxins.

In recent years the marine environment has been seriously damaged by the presence of several toxic phytoplanktonic species, such as dinoflagellates and other toxic algae, which contaminate shellfish and other marine products. Amnesic and paralytic shellfish toxins are examples of these contaminants. The search for sensitive methodologies for the analysis of such compounds is one of the aims of researchers working in the marine environment. High-performance liquid chromatographic methods have been used for this purpose, allowing the detection of very low levels of these toxins. Recently, capillary electrophoresis (CE) has been used as an alternative for the separation and analysis of these compounds. In this paper, we report the optimization of CE procedures for their analysis. Due to the complexity of the matrix, clean-up procedures are required for removing interferences which affect the electrophoretic resolution. The influences of electrophoretic parameters such as voltage, buffer concentrations and organic modifiers, were studied in order to optimize the electrophoretic system to achieve high resolution as well as an accurate quantitation. Extraction and other steps such as clean-up of samples prior to the electrophoretic analysis have been also studied. Different buffers and organic modifiers were used in order to improve the separation of the toxic components, and consequently to obtain accurate quantitative information about the amount of toxins present in the contaminated samples.

Amnesia↗

Further studies on the analysis of DSP toxin profiles in galician mussels.

Further studies on mussel samples from Galicia, Spain, have revealed the presence of okadaic acid (OA), dinophysistoxin 2 (DTX2), and the fatty acid acyl esters of both of these toxins as the "DTX3" complex. Measurements were performed with an improved in situ method for the formation of 9-anthryldiazomethane (ADAM) derivatives followed by liquid chromatography with fluorescence detection. Base hydrolysis of DTX3 toxins gave free OA and DTX2, which were determined following ADAM derivatization. Results were confirmed by liquid chromatography/mass spectrometry analyses, and in most of the samples, free DTX2 was the most abundant toxin. However, the OA/DTX2 ratio in the DTX3 conjugated form was different, with OA being the most abundant in all cases. This difference could be due to different rates of metabolism of OA and DTX2 to the acyl esters or due to contamination of the shellfish by the two toxins at different points in time, resulting in less acyl ester formation for one toxin versus the other. The second possibility would be reasonable if two different source organisms were producing the toxins.

Animals↗

Solid-phase extraction and high-performance liquid chromatography procedures for the analysis of paralytic shellfish toxins.

Paralytic shellfish poisoning (PSP) toxins are produced by certain dinoflagellate species such as Gymnodinium catenatum and Alexandrium tamarensis, during certain periods of the year influenced by several environmental factors, affecting the aquaculture industry and mainly bivalve molluscs. HPLC with fluorescence detection is a powerful analytical technique for the analysis of such toxins; several HPLC alternatives have been developed in order to improve the liquid chromatographic analysis, but due to the complexity of the sample matrix, important work has been focused recently on the clean-up of samples prior to HPLC analysis. Solid-phase extraction procedures offer advantages for this clean-up. In this work we focus on the study of three different clean-up methods prior to HPLC with fluorescence detection analysis of PSP toxin present in contaminated mussel samples; by spiking uncontaminated mussel samples with two different PSP toxin standards and by calculating the recovery values for these experiments. These recoveries must be taken into account in order to quantify the exact amount of PSP toxins present in the contaminated samples.

Animals↗