Biomedical subjects

N Campillo

Publications and source records attributed to N Campillo.

17 recordsLinked to original sources

PubMed2004

Purge-and-trap capillary gas chromatography with atomic emission detection for volatile halogenated organic compounds determination in waters and beverages.

A method for the simultaneous determination of 10 volatile halogenated organic compounds (VHOCs), including four trihalomethanes (THMs), in waters and beverages was developed. The analytes were stripped from the aqueous sample by a flow of helium, preconcentrated in a capillary trap and thermally desorbed using a purge-and-trap (PT) system. This was followed by capillary gas chromatography with microwave-induced plasma atomic emission spectrometry (GC-AED). For element-specific detection, three wavelengths were monitored, corresponding to chlorine (479 nm), bromine (478 nm) and iodine (193 nm). Each chromatographic run took 21 min, including the purge time. After careful choice of the experimental conditions, the performance of the system was evaluated. Calibration curves were obtained by plotting peak area versus concentration and the correlation coefficients for linear calibration were at least 0.9987. Detection limits, calculated for 5 ml sample volume, ranged from 0.05 microg l(-1) for chloroform to 0.5 microg l(-1) for tetrachloromethane. The method was successfully applied to the quantitative analysis of water samples of different origin and also of several beer and juice samples. The tap water samples analyzed contain variable concentrations of the four trihalomethanes, ranging from 1.0 to 66.5 microg l(-1), depending of the compound. Whereas chloroform, bromodichloromethane and bromoform were found in some of the juice samples, only chloroform was detected in the beer samples. The method is reliable and can be used for routine monitoring in water and beverages.

Beverages↗

PubMed2003

Stability of arsenobetaine levels in manufactured baby foods.

The stability of arsenobetaine in baby foods under different experimental conditions is evaluated. Total arsenic was analyzed by electrothermal atomic absorption spectrometry, and the speciation of arsenicals was carried out by coupling liquid chromatography to hydride generation-atomic absorption spectrometry. The highest arsenic levels in the analyzed baby foods corresponded to those containing plaice (2 to 3 microg/g). The speciation data indicated that arsenobetaine, a nontoxic species, was the only arsenical present in the baby foods analyzed at levels between 0.2 and 3 microg/g. Two different procedures for extracting arsenicals from baby foods, involving a water-methanol-chloroform mixture and enzymatic hydrolysis, were tested, and similar results were obtained. Furthermore, the arsenobetaine levels remained unchanged when the baby foods were stored for different times or when the samples were freeze-dried, thus confirming the stability of arsenobetaine and the nonappearance of other arsenic species by interconversion. The reliability of the procedure was checked by analyzing a certified reference material.

Arsenicals↗

PubMed2002

Determination of pesticides in waters by capillary gas chromatography with atomic emission detection.

Capillary gas chromatography with atomic emission detection (GC-AED) was successfully used to separate and quantify 14 pesticides (organochlorines, organophosphorus compounds and pyrethrins) in water samples after liquid-liquid extraction with ethyl acetate. Monitoring the emission lines for elements such as chlorine, bromine and sulfur ensures nearly specific chromatograms for these elements, and markedly increases selectivity. Calibration curves were obtained by plotting peak area versus concentration and the correlation coefficients relating to linearity were at least 0.999. Each chromatographic separation takes 21 min and, since two injections are necessary, it requires approximately 1 h to analyze one sample. The method shows a precision of 4.3-8.2% (RSD), depending on the compound. The application of liquid-liquid extraction with ethyl acetate led to recoveries from spiked samples ranging from 76 to 113%. The sensitivity and linearity for the elements chlorine, sulfur, nitrogen and phosphorus were checked under the optimized conditions at their customary emission wavelength. The sensitivity and linearity for these compounds decreased in the order (atom and emission wavelength) Cl (479 nm)>S (181 nm)>P (178 nm)>N (174 nm). A study of the GC-AED system's response to chlorine concentration in eight pesticide molecules was performed and a linear relationship was found with a correlation coefficient of 0.987.

Calibration↗

PubMed2002

On-line filtration system for determining total chromium and chromium in the soluble fraction of industrial effluents by flow injection flame atomic absorption spectrometry.

Two manifolds were assessed for the purpose of determining both the total chromium content and that present as a soluble form in industrial effluents by flow injection flame atomic absorption spectrometry (FI-FAAS). To determine the chromium content in the soluble fraction the samples were used without additional treatment, a 0.45 microm filter being included in the FI system. To determine the total chromium content, the samples were acidified with nitric acid 20% (v/v) and heated for 30 s in a microwave oven (temperatures of about 70 degrees C were reached). The problem posed by the very different concentration range in which total and soluble chromium are present was overcome by using programmed flow rate methodology and by only partially emptying the sample loop. A personal computer controlled both the rotation speed of a peristaltic pump and the volume of sample injected into the system, thus obtaining the dispersion degree required. Using the manifold proposed, the chromium content in the soluble fraction can be determined in the 0.5-20 microg mL(-1) range using a 10 microg mL(-1) single standard for calibration. To determine the total chromium content, a calibration line in the 20-200 microg mL(-1) range was obtained using a single 50 microg mL(-1) chromium standard solution. The reliability of the semi-automatic devices was verified by comparing the results obtained with those found by treating the samples and using both FAAS in a conventional way and a spectrophotometric method using diphenylcarbazide at the 95% confidence level (ANOVA test). The proposed procedures showed a RSD lower than +/-3%.

Chromium↗

PubMed2001

Sequence-structure homology recognition by iterative alignment refinement and comparative modeling.

Our approach to fold recognition for the fourth critical assessment of techniques for protein structure prediction (CASP4) experiment involved the use of the FUGUE sequence-structure homology recognition program (http://www-cryst.bioc.cam.ac.uk/fugue), followed by model building. We treat models as hypotheses and examine these to determine whether they explain the available data. Our method depends heavily on environment-specific substitution tables derived from our database of structural alignments of homologous proteins (HOMSTRAD, http://www-cryst.bioc.cam.ac.uk/homstrad/). FUGUE uses these tables to incorporate structural information into profiles created from HOMSTRAD alignments that are matched against a profile created for the target from multiple sequence alignment. In addition, environment-specific substitution tables are used throughout the modeling procedure and as part of the model evaluation. Annotation of sequence alignments with JOY, to reflect local structural features, proved valuable, both for modifying hypotheses, and for rejecting predictions when the expected pattern of conservation is not observed. Our stringency in rejecting incorrect predictions led us to submit a relatively small number of models, including only a low number of false positives, resulting in a high average score.

Amino Acid Sequence↗

PubMed2000

Novel bronchodilators: synthesis, transamination reactions, and pharmacology of a series of pyrazino[2,3-c][1,2,6]thiadiazine 2, 2-dioxides.

The synthesis, pharmacological evaluation, and structure-activity relationships of a new class of bronchodilator agents, derivatives of pyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxides are described. The compounds were prepared by reaction of 3,4,5-triamino-1,2, 6-thiadiazine 1,1-dioxide with suitable 1,2-dicarbonyl compounds or alpha-hydroxyiminoketones and subsequent N-alkylation. A transamination procedure for synthesizing derivatives with different substituents at the 4-amino group is reported for the first time. The pyrazino[2,3-c][1,2,6]thiadiazine derivatives were screened for tracheal relaxing activity in vitro, and the active compounds were evaluated in vivo in guinea pigs as bronchodilator agents in comparison to theophylline. Among the compounds studied, the most interesting properties were displayed by the 4-amino-1-ethyl-6-methyl derivative (21). The toxicological evaluation of this derivative is also reported.

Animals↗

PubMed2000

Selenium determination in biological fluids using Zeeman background correction electrothermal atomic absorption spectrometry.

Procedures for the direct determination of total selenium in urine, serum, and blood using electrothermal atomic absorption spectrometry are presented. In the selected experimental conditions, Zeeman correction is mandatory to compensate for the high background signals. The sample diluted and containing 0.1% (w/v) Triton X-100 is introduced directly into the electrothermal atomizer. A solution containing 15% (w/v) hydrogen peroxide, 0.65% (w/v) nitric acid, and 0.5% (w/v) nickel is injected separately into the atomizer. Calibration is carried out using the standard additions method. The detection limit is 30 pg selenium. If palladium, instead of nickel, is used as the chemical modifier, calibration can be carried out against aqueous standards, and the detection limit is 45 pg. In this case, three separate injections are required to prevent precipitation problems in the automatic injector. The reliability of the procedures is checked by analyzing three certified reference materials and by recovery studies. Mean recoveries are 99.7% for serum, 99.4% for urine, and 100.8% for blood samples. Relative standard deviation values are +/-4.0% for serum, +/-3.9% for urine, and +/-4.5% for blood.

Body Fluids↗

PubMed2000

Determination of arsenic in biological fluids by electrothermal atomic absorption spectrometry.

A procedure for the determination of the total content of arsenic in urine, serum and blood by electrothermal atomic absorption spectrometry (ETAAS) is described. Zeeman correction is used to compensate the high background signals. The samples are diluted (1 + 1 for urine and 1 + 3 for both serum and blood samples) in a medium containing 0.1% w/v Triton X-100 before being introduced directly into the furnace. A solution containing 15% w/v hydrogen peroxide, 0.65% w/v nitric acid and 0.5% w/v nickel is also introduced into the atomizer by means of a separate injection. Calibration is carried out against aqueous standards for blood and serum samples and using the standard additions method for urine samples. The detection limit is 20 pg (2 ng ml-1). The reliability of the procedure is checked by analyzing three certified reference materials and by recovery studies.

Arsenic↗

PubMed1999

Novel arylpyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxides as platelet aggregation inhibitors. 2. Optimization by quantitative structure-activity relationships.

In the previous paper (Part 1), we described the synthesis and antiplatelet activity of a series of phenyl- and heteroarylpyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxides. In this paper, we report the optimization of the platelet aggregation inhibitory activity by an iterative sequence of quantitative structure-activity relationship studies which encompassed synthesis and evaluation of the effects of structure variations at the 1-, 6-, and 7-positions of the heterocyclic system. A model has been established that correctly correlates antiplatelet activity in this series with the partial atomic charges calculated by a local density functional ab initio method. As a result of this study, the experimental platelet aggregation inhibitory activity of the lead compound was improved 300-fold.

Animals↗

PubMed1999

Novel arylpyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxides as inhibitors of platelet aggregation. 1. Synthesis and pharmacological evaluation.

A series of N-1-substituted derivatives of pyrazino[2,3-c][1,2, 6]thiadiazine 2,2-dioxides bearing aryl groups at the pyrazino moiety have been prepared. The synthesis involves ring formation between the diaminothiadiazine and suitable dicarbonyl compounds and subsequent introduction of the substituent at N-1. The compounds have been tested in vitro, as inhibitors of rabbit and human platelet aggregation, and ex vivo against rat platelet aggregation induced by arachidonic acid, ADP, collagen, U46619, and I-BOP. The results obtained indicate that some pyrazino[2,3-c][1,2, 6]thiadiazine derivatives show significant platelet aggregation inhibition similar to other antithrombotic agents and that the antiplatelet properties may be mediated by interference with the arachidonic acid pathway.

Animals↗

PubMed1999

An iterative structure-assisted approach to sequence alignment and comparative modeling.

Correct alignment of the sequence of a target protein with those of homologues of known three-dimensional structure is a key step in comparative modeling. Usually an iterative approach that takes account of the local and overall structural features is required. We describe such an approach that exploits databases of structural alignments of homologous proteins (HOMSTRAD, http:/(/)www-cryst.bioc.cam.ac.uk/ approximately homstrad) and protein superfamilies (CAMPASS, http:/(/)www-cryst.bioc.cam.ac.uk/ approximately campass), in which structure-based alignments are analyzed and formatted with the program JOY (http:/(/)www-cryst.bioc.cam.ac.uk/ approximately joy) to reveal conserved local structural features. The databases facilitate the recognition of a family or superfamily, they assist in the selection of useful parent structures, they are helpful in alignment of the target sequences with the parent set, and are useful for deriving relationships that can be used in validating models. In the iterative approach, a model is constructed on the basis of the proposed sequence alignment and this is then reexpressed in the JOY format and realigned with the parent set. This is repeated until the model and sequence alignment is optimized. We examine the case for comparison and use of multiple structures of family members, rather than a single parent structure. We use the targets attempted by our group in CASP3 to assess the value of such procedures.

Algorithms↗

PubMed1997

Use of post-column fluorescence derivatization to develop a liquid chromatographic assay for ranitidine and its metabolites in biological fluids.

Ranitidine and its main metabolites, ranitidine N-oxide and ranitidine S-oxide, were determined in plasma and urine after separation using reversed-phase liquid chromatography. The mobile phase consisted of an initial isocratic step with 7:93 (v/v) acetonitrile-7.5 mM phosphate buffer (pH 6) for 8 min, followed by a linear gradient up to a 25:75 (v/v) mixture over 1 min. Detection was carried out by a post-column fluorimetric derivatization based on the reaction of the drugs with sodium hypochlorite, giving rise to primary amines that reacted with o-phthalaldehyde and 2-mercaptoethanol to form highly fluorescent products. The calibration graphs, based on peak area, were linear in the range 0.1-4 microg/ml for all drugs. The detection limits were 30, 41 and 32 ng/ml (8.6, 12.5 and 9.1 pmol) for ranitidine S-oxide, ranitidine N-oxide and ranitidine, respectively. Chromatographic profiles obtained for plasma and urine samples showed no interference from endogenous compounds.

Anti-Ulcer Agents↗

PubMed1997

Determination of p-hydroxyphenylglycine by reaction with o-phthalaldehyde using a flow-injection fluorimetric procedure.

In the present study, new flow injection procedures for the determination of p-hydroxyphenylglycine using either photometric or fluorimetric detection are proposed. The methods are based on the reaction of the amino acid with o-phthalaldehyde and 2-mercaptoethanol. The calibration graphs based on peak area were linear in the ranges 20-300 ng ml-1 with fluorimetric detection and 5-60 micrograms ml-1 using the photometric mode. The detection limit calculated for the fluorimetric procedure was 10 ng ml-1. The method was applied to the determination of the free p-hydroxyphenylglycine present in industrial pharmaceutical samples of a Dane salt.

Flow Injection Analysis↗

PubMed1997

Heterocyclic structures useful in medicinal chemistry: the case of pyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxide.

Different aspects of a particular kind of heterocycle, namely pyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxide are discussed. These include synthesis, reactivity, tautomerism and acid-base properties, results of x-ray analysis and molecular orbital calcultations. Besides, some of the derivatives have shown interesting biological effects, among which are the diuretic properties which are also presented.

Animals↗

PubMed1996

Indirect flame atomic absorption detection for the liquid chromatographic separation of alkaline metals.

Alkaline metals and ammonium ion are separated by cationic exchange liquid chromatography using a 60 microg ml(-1) aqueous copper solution as the mobile phase at 1.5 ml min(-1). Detection is carried out by measuring copper with an atomic absorption spectrometer directly interfaced to the chromatograph. A simple T-piece is used to compensate the difference between the nebulizer uptake rate and the chromatographic flow-rate with air. The method is applicable to the analysis of alkaline metals and ammonium in waters. Average recovery ( n = 16) was 100.3 +/- 4.0%.

Journal Article↗

PubMed1996

Extending the dynamic range of flame atomic absorption spectrometry: a comparison of procedures for the determination of several elements in milk and mineral waters using on-line dilution.

Three approaches based on continuous flow methodology are assessed for the purpose of extending the dynamic range of flame atomic absorption spectrometry. The determination of several elements in infant liquid and powdered milk and water samples is used to check the performances of the manifolds. Two of the systems are fully computer-controlled and permit a calibration graph to be obtained by using a single standard solution. The results confirm that continuous flow methodology is a reliable alternative to the time-consuming common dilution procedures based on glassware. Since the systems are versatile and permit a wide range of degrees of dilution to be obtained, they can be easily adapted for the automated or semi-automated analysis of other liquid samples which are too concentrated to be aspirated directly into the atomic absorption spectrometer.

Journal Article↗

PubMedDate not supplied

Fast determination of lead and copper in dairy products by graphite furnace atomic absorption spectrometry.

A rapid and direct procedure for determining lead and copper in dairy products by electrothermal atomic absorption spectrometry (ETAAS) is described. Samples are slurried in a medium containing 50% v/v hydrogen peroxide, 1% v/v nitric acid, 0.5% w/v dihydrogen phosphate, and 20% v/v ethanol and directly injected into the furnace with no previous mineralization. Calibration is performed with aqueous standards. Limits of determination were 0.4 and 2.4 ng/mL for copper and lead, respectively. The reliability of the procedure was checked by comparison with the acid mineralization procedure and by analyzing 3 certified reference milk samples.

Calibration↗