Biomedical subjects

Francisco Merino

Publications and source records attributed to Francisco Merino.

7 recordsLinked to original sources

PubMed2005

Stability of benzalkonium surfactants on hemimicelle-based solid-phase extraction cartridges.

The capability of hemimicelle-based solid-phase extraction cartridges for the preservation of organic compounds after their concentration from water samples was investigated for the first time. The approach is illustrated by studying the stability of benzalkonium homologue (C12, C14 and C16) surfactants (BAS) on monolayers of dodecyl sulphate (SDS) hemimicelles formed on alumina. The stability study included storage of cartridges at room temperature, at 4 and -20 degrees C, during a period of up to 3 months. The influence of water matrix components was also investigated from parallel experiments using spiked distilled, river and wastewater samples. Complete recovery of BAS was obtained for all storage conditions tested. Recoveries were independent on the alkyl chain length of BAS homologues and water matrix. The SPE of BAS on the SDS hemimicelles had a strong stabilizing effect for the target compounds and their analysis can be accomplished after at least 3 months without the necessity of special storage conditions for cartridges. Because of the lack of data, an additional stability study was carried out for BAS in an aqueous matrix using traditional preservation methods such as acidification (pH 2)/refrigeration, addition of formaldehyde (5%)/refrigeration, and freezing (-20 degrees C). Only combination of chemical addition (e.g. nitric acid or formaldehyde)/refrigeration was found effective to preserve BAS in the short term (e.g. for a week), then losses up to 40% were observed for these target compounds after a month.

Benzalkonium Compounds↗

PubMed2005

Supramolecular systems-based extraction-separation techniques coupled to mass spectrometry.

The combination of supramolecular chemistry and MS has not only been fruitful in the field of gas-phase fundamental studies of host-guest complexes and supramolecular assemblies. Mass spectrometric analysis has also benefited from the ability of supramolecular systems to behave as pseudophases in which solutes partition from the bulk solvent phase. Supramolecular systems-based extraction and concentration schemes and separation techniques have been widely used in different fields of analytical chemistry and are ideally suited for coupling with MS. This review describes the present status of the application of supramolecular chemistry in mass spectrometric analysis and includes topics such as the use of coacervative liquid-liquid extraction and hemimicelle/admicelle-based SPE of organic compounds prior to chromatography and electrophoresis. It also discusses the recent advances in enantioselective analysis using CD in electrophoresis- and chromatography-MS. The potential and analytical challenges of these approaches in environmental and bioanalytical chemistry, where one can expect significant developments in the future, are outlined.

Journal Article↗

PubMed2004

Apoptotic cell death dynamics of HL60 cells studied using a microfluidic cell trap device.

This paper presents the design, fabrication and first results of a microfluidic cell trap device for analysis of apoptosis. The microfluidic silicon-glass chip enables the immobilization of cells and real-time monitoring of the apoptotic process. Induction of apoptosis, either electric field mediated or chemically induced with tumour necrosis factor (TNF-alpha), in combination with cycloheximide (CHX), was addressed. Exposure of cells to the appropriate fluorescent dyes, FLICA and PI, allows one to discriminate between viable, apoptotic and necrotic cells. The results showed that the onset of apoptosis and the transitions during the course of the cell death cascade were followed in chemically induced apoptotic HL60 cells. For the case of electric field mediated cell death, the distinction between apoptotic and necrotic stage was not clear. This paper presents the first results to analyse programmed cell death dynamics using this apoptosis chip and a first step towards an integrated apoptosis chip for high-throughput drug screening on a single cellular level.

Apoptosis↗

PubMed2004

Evaluation and optimization of an on-line admicelle-based extraction-liquid chromatography approach for the analysis of ionic organic compounds.

Admicelles-based solid-phase extraction (SPE) was on-line coupled with liquid chromatography/electrospray ionization/ion trap mass spectrometry, and it was proposed for the extraction of ionic organic compounds based on the formation of surfactant-analyte ion pairs. The approach was illustrated by studying the preconcentration of quaternary ammonium herbicides (quats) on sodium dodecyl sulfate (SDS) admicelles produced on alumina. Optimization of the parameters affecting SPE were studied on the basis that admicelles are dynamic entities in equilibrium with the aqueous phase. Some general guidelines could be established for method development from the results obtained. Factors influencing on-line operation were elucidated. On-line regeneration of the sorbent in each run was easily achieved by disruption of SDS admicelles with methanol and posterior coating of the alumina with SDS. The recovery of quats from drinking water samples were found quantitative for paraquat, diquat, and difenzoquat and above to 70% for chlormequat and mepiquat. Concentration factors of about 250, using sample volumes of 50 mL, were achieved. The detection limits ranged from 10 to 30 ng/L. The approach developed permits compliance with the directives of the European Community for drinking waters (100 ng/L) and goes deeply into the basis of solid-phase extractions that use surfactant-coated mineral oxide as sorbents.

Journal Article↗

PubMed2003

Solid-phase extraction of amphiphiles based on mixed hemimicelle/admicelle formation: application to the concentration of benzalkonium surfactants in sewage and river water.

The capability of surfactant-coated mineral oxides to aid the solid-phase extraction (SPE) of amphiphiles based on the formation of mixed hemimicelles/admicelles was investigated. The approach is illustrated by studying the adsolubilization of benzalkonium homologue (C(12), C(14), C(16)) surfactants (BAS) on sodium dodecyl sulfate (SDS)-coated alumina. These oppositely charged surfactants form mixed aggregates on alumina causing retention of BAS by strong hydrophobic and ionic interactions. The recovery of BAS was found quantitative and independent of the alkyl chain length under a wide range of experimental conditions (3-200 mg of SDS/g of alumina; pH 2-11; sample flow rate 3-20 mL/min, and sample loading volume 0.025-1 L). Anionic and nonionic surfactants and electrolytes did not interfere to the levels found in raw sewage. Combination of BAS adsolubilization-based SPE with liquid chromatography/electrospray ionization in positive ion mode/ion trap mass spectrometry permitted the quantification of BAS with detection limits of 4 ng/L and their identification by isolation and subsequent fragmentation in the ion trap. The approach developed was applied to the determination of BAS in raw and treated sewage and river samples. The concentrations of benzalkonium surfactants found ranged between 0.1 and 49 microg/L.

Journal Article↗

PubMed2003

Mixed aggregate-based acid-induced cloud-point extraction and ion-trap liquid chromatography-mass spectrometry for the determination of cationic surfactants in sewage sludge.

Alkyl ammonium surfactants were extracted and concentrated from sludge samples using the acid-induced cloud-point extraction (ACPE) technique. Reversed-phase liquid chromatography-electrospray ionization in positive ion mode ion-trap mass spectrometry was then used for the separation, quantitation and identification of single homologues of the cationic surfactants. Variables affecting the ACPE efficiency were optimized using a spiked activated sludge. Total method recoveries ranged from 91 to nearly 100%. Detection limits for cationics in the sludge were between 40 and 75 ng/g. The analysis of cationic surfactants in activated and dehydrated sludge collected from two different sewage treatment plants revealed the presence of dialkyldimethyl, alkylbenzyldimethyl and alkyltrimethyl ammonium in the concentration range from 0.1 to 34 mg/kg. Alkylpyridinium surfactants were not detected. The persistence of alkyl ammonium surfactants in sewage sludge after treatments applied at municipal sewage plants was confirmed.

Acids↗

PubMed2002

Acid-induced cloud point extraction and preconcentration of polycyclic aromatic hydrocarbons from environmental solid samples.

The effectiveness of the acid-induced phase separation of anionic surfactants (acid-induced cloud point extraction, ACPE) to extract polycyclic aromatic hydrocarbons (PAHs) from different environmental samples (soils, sediments and sludges), prior to chromatographic analysis, was evaluated. Variables affecting the ACPE efficiency were optimised using a natural matrix (a harbour sediment, CRM 535). Temperature, surfactant concentration and stirring were of primary importance to maximise recovery, whereas temperature and surfactant/hydrochloric acid concentration influenced the volume of the surfactant-rich phase and therefore the preconcentration factor achieved. The optimal conditions (2% sodium dodecanesulphonate (SDoS), 4.2 M HCl, 60 degrees C, 1 h) were applied to the extraction of PAHs from various matrices and the ACPE recoveries compared to certified results from Soxhlet extractions. Recoveries obtained for four to five aromatic ring PAHs ranged from 71 to 98%. Uncertainties obtained using ACPE were similar to or lower than those provided for the certified values. The volume of the extracts ranged from 1 to 2 ml. The method did not require additional clean-up or preconcentration steps.

Acids↗