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L Ramos

Publications and source records attributed to L Ramos.

At least 37 records · Page 2Linked to original sources
PubMed2001

Solid-phase microextraction method for the determination of atrazine and four organophosphorus pesticides in soil samples by gas chromatography.

A simple and rapid solid-phase microextraction (SPME) based method is presented for the simultaneous determination of atrazine and four organophosphorus (i.e. parathion-methyl, chlorpyriphos, methidathion and carbophenothion) in soils. After optimisation of the different experimental variables affecting the SPME of the target compounds from aqueous solutions by using an experimental design, a consensus strategy was adopted which allowed the use of the SPME method developed for the simultaneous screening of all the analytes selected. The complete analytical procedure finally proposed consisted of a 15-min ultrasonic extraction of the target compounds from a 0.5-g soil sample with 5 ml of methanol and the dilution of this extract to up 10% methanol followed by the addition of NaCl to a final concentration of 10% (w/v). The analytes in this aqueous extract were preconcentrated for 30 min in the SPME fiber and subsequently desorbed by heating of the fiber at 260 degrees C for 5 min in the gas chromatograph injection port. Final determination was carried out with an electron-capture detector. The recoveries of the pesticides studied in soils ranged from 72 to 123%, except for atrazine, and the SDs were below 16%. The feasibility of the procedure finally proposed for the screening of the endogenous pesticides irrespective of the properties of the soil selected has been shown.

Atrazine↗
PubMed2001

Ultraslow dynamics and stress relaxation in the aging of a soft glassy system.

We use linear rheology and multispeckle dynamic light scattering (MDLS) to investigate the aging of a gel composed of multilamellar vesicles. Light scattering data indicate rearrangement of the gel through an unusual ultraslow ballistic motion. A dramatic slowdown of the dynamics with sample age t(w) is observed for both rheology and MDLS, the characteristic relaxation time scaling as t(mu)w. We find the same aging exponent mu = 0.78 for both techniques, suggesting that they probe similar physical processes, that is the relaxation of applied or internal stresses for rheology or MDLS, respectively. A simple phenomenological model is developed to account for the observed dynamics.

Journal Article↗
PubMed2001

Scaling with temperature and concentration of the nonlinear rheology of a soft hexagonal phase.

The nonlinear rheology of a soft surfactant hexagonal phase is examined. The system exhibits a shear-melting transition from a two-dimensional polycrystalline texture to a liquid of cylinders aligned along the flow [Ramos et al., Langmuir 16, 5846 (2000)]. This dynamic transition is associated with a discontinuity in the stress-strain curve (flow curve). A detailed study of the temperature and concentration dependence of the flow curves is presented. The nonlinear rheology is found to display a scaling behavior, when temperature or concentration are varied. We demonstrate that the whole behavior of the hexagonal phase under shear is essentially governed by the linear shear modulus of the sample, G0. When temperature is varied, we show that the two key parameters, which control G0 and in turn, the flow curve, are a transition temperature T(c) and an activation energy E(A). We propose E(A) to be related to the scission energy of one cylinder into two pieces.

Journal Article↗
PubMed2001

Suitability of several carbon sorbents for the fractionation of various sub-groups of toxic polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans.

Feasibility of several sorbents, Amoco PX-21, Carbosphere, Carbopack B and C and 2-(1-pyrenyl) ethyldimethylsilylated silica gel (PYE), for the fractionation of polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins and furans was investigated. Selection was based on their suitability for quantitative isolation of the target compounds with special attention for the most toxic mono- and non-ortho-CBs to prevent coelution with other congeners during the final determination by gas chromatography. Cost-effectiveness in terms of solvent and time consumption as well as feasibility for routine analysis and automation were considered additional merits of the methods compared. Final evaluation of the procedures providing the best results was done by comparison of the results obtained from the analysis of real-life samples. The results showed that, among the sorbents tested, Carbopack B and PYE were the most suitable for routine analysis. In particular, these sorbents allowed a more reliable determination of the toxic congeners and, consequently, of the toxic equivalents of 2,3,7,8-tetrachlorodibenzo-p-dioxin content in environmental samples.

Benzofurans↗
PubMed2001

Miniaturized automated matrix solid-phase dispersion extraction of pesticides in fruit followed by gas chromatographic-mass spectrometric analysis.

In this study a simple and fast miniaturized automated matrix solid-phase dispersion method for the sample preparation and quantitative extraction of pesticides was developed and evaluated. Only 25 mg of sample and 100 microl of organic solvent were used per analysis for this new miniaturized set-up. The extracts were subsequently analysed by GC-MS without any further purification. The method was optimized for oranges and tested for the determination of a variety of organophosphorus pesticides and a pyrethroid at concentration levels below the maximum residue levels set by the European Union and authorities in The Netherlands. The limits of detection were 4-90 microg/kg. The recoveries for pesticides in orange were 83-118% and the relative standard deviations for the total procedure were 10-13% (n=4) at the limit of quantification. The feasibility of the developed method for apple, pear and grapes was also studied. Equally good results were obtained, but for apple the washing step should be omitted.

Automation↗
PubMed2001

Distribution of aflatoxin M1 in cheese obtained from milk artificially contaminated.

Small-scale manufacture of cheese using artificially AFM1 contaminated milk as raw material to study the distribution of such toxin both in whey and in cheese, was carried out. Whole milk with undetectable levels of AFM1 was used. The toxin was added in concentration that varied from 1.7 to 2.0 microg/l of milk. After the home-made production of cheese, the concentration of AFM1 was determined both in whey and in cheese, using the enzymatic immunoassay technique. The greatest proportion, 60%, was detected in whey while 40% AFM1 remained in cheese.

Aflatoxin M1↗
PubMed2001

Use of atmospheric pressure ionization mass spectrometry in enantioselective liquid chromatography.

Recent advances in mass spectrometry have rendered it an attractive and versatile tool in industrial and academic research laboratories. As a part of this rapid growth, a considerable body of literature has been devoted to the application of mass spectrometry in studies involving enantioselectivity, molecular recognition, and supramolecular chemistry. In concert with separation techniques such as capillary electrophoresis and liquid chromatography, mass spectrometry allows rapid characterization of a large array of molecules in complex mixtures. A majority of these findings have been made possible by the introduction of 'soft-ionization' techniques such as electrospray ionization interface. Other techniques such as atmospheric pressure chemical ionization mass spectrometry have been widely used as a rugged interface for quantitative liquid chromatography-mass spectrometry. Herein, we present a brief overview of the above techniques accompanied with several examples of enantioselective capillary electrophoresis- and liquid chromatography-mass spectrometry in drug discovery and development. Although the emphasis of this article is on quantitative enantiomeric chromatography-mass spectrometry, we envisage that similar strategies are adaptable in qualitative studies.

Atmospheric Pressure↗
PubMed2001

Case report. Cutaneous cryptococcosis in a patient with systemic erythematous lupus.

The first case of a cutaneous cryptococcosis associated with systemic erythematous lupus (SLE) diagnosed in our Mycology Reference Centre is presented: a 24-year-old female patient diagnosed with SLE, nephrotic syndrome, arterial hypertension, renal insufficiency due to glomerulonephritis type IV and cellulitis in the right thigh and gluteus. Cryptococcus neoformans was isolated by cutaneous biopsy and haemoculture. Cryptococcal antigen was detected in serum by the latex agglutination test. As the patient did not respond to fluconazol intravenous treatment, amphotericin B administration was performed. She died of acute renal insufficiency.

Adult↗
PubMed2001

Low rates of DNA fragmentation in selected motile human spermatozoa assessed by the TUNEL assay.

BACKGROUND: In this study we present the physiological changes observed in ejaculated spermatozoa of normospermic men after exposure to hydrogen peroxide (H(2)O(2)) or gamma irradiation. METHODS: Motility changes as well as membrane and DNA-damage were determined in spermatozoa after incubation with 25 micromol/l of H(2)O(2) during increasing intervals of time (0--60 min and after 24 h) or after irradiation of cells using alpha rays. Annexin V-binding in combination with propidium iodide was used for the assessment of membrane changes after each incubation time. TdT-mediated-dUTP nick-end labelling (TUNEL) was used to evaluate DNA damage. RESULTS: After 1 h incubation of the spermatozoa with H(2)O(2), almost all cells were positive for Annexin-V, while no significantly increase in TUNEL positivity was observed. TUNEL results were significantly higher 24 h after incubation with H(2)O(2) (10--16.3%, P = 0.03). In the control group (cumulus cells), an increase in the percentage of TUNEL positive cells was observed after 15 min of incubation with H(2)O(2) and showed a five-fold increase after 24 h (from 8.1-72.1%, P < 0.001). TUNEL positive cells after alpha irradiation increased with the doses and post-irradiation time (from 10.8--47.2%). Interestingly, when only motile spermatozoa from irradiated samples were analysed, only 0.5% were TUNEL positive. CONCLUSION: Motility may be a relevant physiological marker for DNA-intact sperm after exposure of spermatozoa to H(2)O(2) and alpha irradiation.

Annexin A5↗
PubMed2000

Assessment of methods for tissue-based detection of the HER-2/neu alteration in human breast cancer: a direct comparison of fluorescence in situ hybridization and immunohistochemistry.

PURPOSE: To compare the efficacy of fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC) in detecting the HER-2/neu alteration in human breast cancer. PATIENTS AND METHODS: Unselected stage I, II, and III breast cancer patients (N = 900) were tested for HER-2/neu gene amplification by FISH in paraffin-embedded, formalin-fixed archival material. Of these samples, 856 were tested for HER-2/neu overexpression by non-antigen-retrieval IHC with the polyclonal antibody R60, the sensitivity and specificity of which was preliminarily compared with the United States Food and Drug Administration-approved HercepTest (Dako Corp, Carpinteria, CA). Patient survival was analyzed in relation to the presence of the HER-2/neu alteration as determined by these two methodologies. RESULTS: A total of 189 (21%) of 900 patients were positive by FISH and 147 (17.2%) of 856 were positive by IHC. This discrepancy is consistent with expected loss of IHC sensitivity associated with tissue fixation/embedding. The HercepTest did not improve sensitivity and introduced false positives. Comparison of R60-based IHC with FISH demonstrates that patient survival is associated progressively to gene amplification level as determined by FISH, whereas for IHC an association is found only in the highest (3+) immunostaining group. Among FISH-negative tumors, 45 (6.6%) of 678 were IHC-positive, with a survival probability similar to that of FISH-negative/IHC-negative cases; FISH-positive/IHC-negative patients have a survival probability similar to that of FISH-positive/IHC-positive cases. CONCLUSION: IHC does not consistently discriminate patients likely to have a poor prognosis, whereas FISH provides superior prognostic information in segregating high-risk from lower-risk beast cancers. HER-2/neu protein overexpression in the absence of gene amplification occurs infrequently in breast cancer, in which case, patient outcome is similar to that of patients without the alteration.

Adult↗
PubMed2000

Miniaturised pressurised liquid extraction of polycyclic aromatic hydrocarbons from soil and sediment with subsequent large-volume injection-gas chromatography.

Analyte extraction is the main limitation when developing at-line, or on-line, procedures for the preparation of (semi)solid environmental samples. Pressurised liquid extraction (PLE) is an analyte- and matrix-independent technique which provides cleaner extracts than the time-consuming classical procedures. In the study, the practicality of miniaturised PLE performed in a stainless-steel cell, and combined with subsequent large-volume injection (LVI)-GC-MS was studied. As an example, the new system was applied to the determination of polycyclic aromatic hydrocarbons (PAHs) in soils and a sediment. Variables affecting the PLE efficiency, such as pressure and temperature of the extraction solvent and total solvent volume, were studied. Toluene was selected as extraction solvent and a total solvent volume of 100 microl was used for the 10 min static-dynamic PLE of 50-mg samples. Additional clean-up or filtration of the sample extracts was not required. Detection limits using LVI-GC-MS were below 9 ng/g soil for the 13 PAHs more volatile than indeno[1,2,3-cd]pyrene in real soil samples and the repeatability of the complete PLE plus LVI-GC-MS method for the analysis of the endogenous PAH was better than 15%. Comparison of PLE and Soxhlet or liquid-partitioning extraction results for the analysis of non-spiked samples showed that the efficiency of PLE is the same or better than for the other two extraction methods assayed.

Gas Chromatography-Mass Spectrometry↗
PubMed2000

Liquid-liquid extraction using 96-well plate format in conjunction with liquid chromatography/tandem mass spectrometry for quantitative determination of methylphenidate (Ritalin) in human plasma.

Methylphenidate (MPH; Ritalin: methyl-alpha-phenyl-2-piperidinacetate hydrochloride) is utilized for the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy. Recently, we described a rapid enantioselective liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for the determination of the enantiomers of MPH (Rapid Commun. Mass Spectrom. 1999; 13: 2054). A lower limit of quantification (LLOQ) of 87 pg/mL was attained for the human plasma assay. The present paper describes a high-throughput sample preparation procedure in conjunction with racemic LC/MS/MS analysis for MPH with a LLOQ of 50 pg/mL. A semi-automated robotics method using liquid-liquid extraction (LLE) in a 96-well plate format was developed and validated. The correlation coefficients were > or =0.998 for MPH indicating good fits of the regression models over the range of the calibration curve. The accuracy and precision of the semi-automated approach were comparable to those obtained using the manual sample preparation technique reported previously (vide supra). The current method can easily be adapted to the enantioselective LC/MS/MS assay of MPH. The assay was simple, fast, specific, and exhibited excellent ruggedness.

Attention Deficit Disorder with Hyperactivity↗
PubMed2000

High-throughput approaches to the quantitative analysis of ketoconazole, a potent inhibitor of cytochrome P450 3A4, in human plasma.

Ketoconazole, an imidazole-piperazine compound, is an orally active antimycotic agent. In addition, ketoconazole is a specific inhibitor of cytochrome P450 3A4. As about 60% of oxidized drugs are biotransformed by this isoform, the potential effect of a concomitant administration of ketoconazole on drug disposition may be of interest during drug development. The present paper describes three different approaches (methods A, B, and C) to attain high-throughput sample preparation and analysis in the quantification of ketoconazole in human plasma. Method A consisted of acetonitrile precipitation in a 96-well plate, transfer of the supernatant via a Tomtec Quadra 96 Model 320, and subsequent injection onto a 50 x 4.6 mm (i.d.) Develosil Combi-RP-5 column (packed with C30 bonded silica particles). Method B consisted of an identical sample preparation to method A with the exception that a Michrom Magic Bullet(trade mark) column, 2.0 --> 0.50 mm (i.d., tapered bore) x25 mm length, was used. Lastly, in method C, a turbulent-flow chromatography (TurboFlow LC/APCI-MS/MS) module was used for the direct analysis of ketoconazole in human plasma. A Sciex API 3000 was used in methods A and B, while a Micromass Quattro LC was employed in method C. Based on the values obtained for the calibrator (standard) and quality control samples, all three protocols yielded satisfactory accuracy, precision, and reduced manual sample preparation time.

Antifungal Agents↗