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Biomedical subjects

D Pérez-Bendito

Publications and source records attributed to D Pérez-Bendito.

At least 19 recordsLinked to original sources
PubMed2004

Ion trap LC/MS characterisation of toxic polar organic pollutants in colour photographic wastewaters and monitoring of their chemical degradation.

Liquid chromatography/electrospray ionisation-ion trap mass spectrometry (LC/ESI-ITMS) with positive mode of operation was successfully applied to the characterisation of aromatic amines and chelating agents in colour photographic wastewaters. In addition to residual ingredients, monomers and dimers of sulphonated aromatic amines were the main toxic polar organic pollutants found. Oxidation of wastewater components by the Fenton-like reagent (Fe3+ + H2O2) was investigated by continuously pumping a solution of hydrogen peroxide. Iron concentration, present in the wastewater as ferric carboxylate complexes, was typically above 1 g l(-1), and therefore addition of Fe3+ was not necessary for treatment. Operating variables like reagent feeding concentration and flowrate, temperature and pH were studied. The overall chemical oxygen demand (COD) removal reached 90% after 7.5 h of treatment when the dosage of hydrogen peroxide was 230 g per litre of effluent, the pH was about 4 and the temperature was 60 degrees C. The absence of toxics in the treated effluents was confirmed by the Photobacterium phosphoreum luminescence reduction test. Monitoring of the chemical degradation of aromatic amines and chelating agents by LC/ESI-ITMS proved that the Fenton's like reagent was effective in degrading them. Propylenediamine tetraacetic acid (PDTA) was found to be the more recalcitrant compound, however about 97% of degradation was achieved after 7.5 hours of treatment.

Amines↗
PubMed2001

Determination of dialkyldimethylammonium surfactants in sewage based on the formation of premicellar aggregates.

A method is described for the determination of dialkyldimethylammonium surfactants (DDAS) in sewage, based on the formation of premicellar aggregates with sodium dodecyl sulfate and using the dye Coomassie Brilliant Blue G (CBBG) as a photometric probe. The mixed aggregates are selectively obtained at DDAS concentrations three orders of magnitude below the critical micelle concentration. As a result, DDAS can be determined at the microg l(-1) level without interference from other quaternary ammonium/pyridinium or anionic/non-ionic surfactants. Because of the selectivity of the method, the clean-up of sewage influents and effluents only involves extraction with chloroform, after formation of the DDAS-sodium dodecane sulfonic acid ion pair, evaporation of the extracts to dryness and dissolution of DDAS in 4 M hydrochloric acid. The recovery of DDAS ranged from 82 to 93% and from 100 to 105% in sewage influents and effluents, respectively.

Journal Article↗
PubMed2000

Simultaneous stopped-flow determination of butylated hydroxyanisole and propyl gallate using a T-format luminescence spectrometer.

A simple and fast luminescent method is used for the first time to resolve a mixture of two synthetic antioxidants, propyl gallate (PG) and butylated hydroxyanisole (BHA), by the joint use of the stopped-flow mixing technique and a T-format luminescence spectrometer. The determination of these compounds involves two different and independent reactions. On the one hand, PG determination is based on an energy transfer process that involves the formation of a lanthanide chelate with terbium in the presence of Triton X-100 and tri-n-octylphosphine oxide. On the other hand, BHA is determined using a reaction between the oxidized form of Nile Blue and the antioxidant. Both systems are excited at the same excitation wavelength (310 nm), and the emission wavelengths are 545 and 665 nm for PG and BHA, respectively. The absence of overlap in the emission spectra makes it possible to measure separately the analytes in each channel of the instrument. Initial rate and equilibrium signal are used as analytical parameters and measured in 0.1 and 1 s for PG and BHA, respectively. Calibration graphs are linear over the range 0.09-3.5 microg mL(-)(1) for PG and 0.3-15 microg mL(-)(1) for BHA. The relative standard deviations of both systems are close to 2%. The proposed method is applied to the determination of these two antioxidants in several commercial food samples with recoveries ranging between 94.8 and 102.9% for PG and between 94.1 and 102.1% for BHA.

Butylated Hydroxyanisole↗
PubMed1999

Multi-residue analysis of N-methylcarbamate pesticides and their hydrolytic metabolites in environmental waters by use of solid-phase extraction and micellar electrokinetic chromatography.

A method for the simultaneous separation and determination of N-methylcarbamate pesticides and their hydrolytic metabolites by micellar electrokinetic chromatography (MEKC) was developed. A mixture of five pesticides (carbaryl, propuxur, carbofuran, aminocarb, and methiocarb) and their corresponding phenols was studied to optimize the separation of its components in terms of various electrophoretic parameters such as buffer type, pH and concentration, sodium dodecyl sulfate concentration, injection conditions, and applied voltage. Excellent separation of all ten analytes was achieved within about 20 min. The optimized method was used for determinations in environmental water samples. Sample volumes of 250 mL were first preconcentrated in the pesticides and metabolites by passage through a LiChrolut EN sorbent column and then further enriched by on-column stacking. Dynamic ranges of 40 ng/L - 6 microg/L, limits of detection at the nanogram-per-liter level, and relative standard deviations from 2.6 to 7.4% were obtained. The proposed method surpasses high-performance liquid chromatography (HPLC) in separation efficiency. In fact, it provides more expeditious separations and allows more flexible adjustment of the selectivity. Also, it enables the quantification for the analytes studied in this work with decreased limits of detection.

Carbamates↗
PubMed1999

Simultaneous determination of benzoic acid and saccharin in soft drinks by using lanthanide-sensitized luminescence.

A simple and fast approach is used for the first time to develop a time resolved lanthanide-sensitized luminescence method for the simultaneous determination of a preservative and a sweetener, namely benzoic acid (BZ) and saccharin (SC), respectively, in food samples. The method involves the formation of the corresponding ternary chelates with terbium(III) and trioctylphosphine oxide (TOPO) in the presence of Triton X-100, and the measurement of the initial rate and equilibrium signal of this system, which were obtained in 0.1 and 5 s, respectively. The dynamic ranges of the calibration graphs, obtained by using kinetic and equilibrium measurements, were 0.2-36 micrograms ml-1 and 0.15-30 micrograms ml-1, respectively, for BZ, and 3.3-24 micrograms ml-1 and 4-36 micrograms ml-1 for SC and the detection limits were 0.07 and 0.04 microgram ml-1, respectively, for BZ, and 1.1 and 1.2 micrograms ml-1, respectively, for sodium SC. The relative standard deviation ranged between 2.3 and 3.0%. Both compounds were determined simultaneously by using a system of two equations which were resolved by using the calibration data obtained individually for each analyte and by multiple linear regression. Mixtures of BZ and SC in ratios between 3:1 and 1:9 were satisfactorily resolved by using both approaches. The method was applied to the direct analysis of several soft drinks. Analytical recoveries ranged between 89.3 and 108.5%.

Benzoic Acid↗
PubMed1998

Quantitation of tricyclic antidepressant drugs based on the formation of mixed aggregates with surfactants.

A new approach for the quantitation of drugs, based on the measurement of the critical micelle concentration of mixed surfactant-drug aggregates, is proposed. This methodology involves the photometric titration of drugs in an aqueous medium using a surfactant as titrant. The Coomassie Brilliant Blue G (CBBG) dye, negatively charged, is used as a photometric probe. The analytical applicability of this approach is demonstrated by quantifying tricyclic antidepressants (TCAs) such as imipramine, desimipramine, amitriptylin, and nortriptylin. Aggregates studied included TCA-sodium dodecyl sulfate (SDS) and TCA-Triton X-100 mixtures. Because of the opposite charge of TCAs and SDS, which causes strong synergistic effects in the mixture relative to the properties of their individual components, this anionic surfactant was selected for the quantitation of TCAs. Pharmaceutical preparations can be analyzed directly after dissolution of the samples in water or ethanol. The detection limit achieved for the studied drugs is about 0.12 mg L-1, so the proposed method surpasses existing alternative photometric methods in sensitivity and features a detection limit similar to fluorimetric methods. The relative standard deviation for 0.8 mg L-1 of TCA is 2.6%.

Antidepressive Agents, Tricyclic↗
PubMed1998

Determination of antihistamines based on the formation of mixed aggregates with surfactants.

The determination of antihistamines based on the measurement of the critical micelle concentration (c.m.c.) of mixed sodium dodecyl sulfate (SDS)-antihistamine aggregates is proposed. The dye Coomassie Brilliant Blue G (CBBG) was used as a photometric probe for the rapid determination of c.m.c.s. The micellar properties of these drugs permitted the determination of diphenhydramine, antazoline, tripelennamine, diphenylpyraline and clemizole at the micron level with detection limits ranging between 0.1 and 0.7 microns. Hence the proposed method surpassed existing alternative photometric methods used routinely in the quality control of these drugs in sensitivity and featured similar detection limits to fluorimetric methods. The relative standard deviation for 6 micron diphenhydramine was 3.7%. The method was applied to the determination of these drugs in pharmaceutical preparations (solutions, capsules, creams and pills). which were analyzed directly after dissolution of the samples in distilled water.

Antazoline↗
PubMed1996

Advances in drug analysis by kinetic methods.

Automatic kinetic methods are powerful tools for drug analysis as they use modern instrumentation and computers, which are essential for shortening analysis times and enhancing the quality of routine analyses. This paper reviews novel kinetic approaches to the determination of various types of drugs in bio(pharmaceutical) materials including the following: (a) a combination of the stopped-flow (SF) technique and fluorescence polarization immunoassay for the determination of drugs of abuse and opiates in urine; (b) the joint use of the SF technique and micelle-stabilized room-temperature phosphorimetry for the determination of anti-inflammatory drugs such as naproxen; (c) the use of sensitized luminescence by energy transfer processes for the kinetic determination of antibiotics such as tetracycline using the SF technique; and (d) the use of the continuous addition of reagent technique for determining hallucinogenic alkaloids and phenothiazines by peroxyoxalate chemiluminescence reactions. Other advances in drug analysis by kinetic methods involving kinetometric approaches (e.g. Kalman filtering) and the use of micellar catalysis are also discussed.

Chemistry Techniques, Analytical↗
PubMed1996

Kinetic fluorimetric determination of gliadins in foods.

Kinetic methodology was applied for the first time to the determination of gliadin proteins by using a stopped-flow mixing technique. The method is based on two simultaneous processes: the reaction between gliadins and sodium dodecyl sulfate and the elimination of the quenching caused by this surfactant of the fluorescence of Cresyl Violet. Thus, the increase in fluorescence intensity with time is directly related to gliadin concentration. The use of this oxazine dye allows dynamic fluorescence measurements at long wavelengths, which avoids potential interferences from the sample matrix. The reaction rate is measured within 5 s, so the method is very suitable for the routine determination of gliadins in food samples. The dynamic range of the calibration graph was 0.5-50 micrograms ml-1 and the LOD was 0.25 microgram ml-1. The RSD was 1.6%. The method was applied to different food samples and the analytical recoveries were 88-107%.

Fluorometry↗
PubMed1996

Simultaneous spectrophotometric determination of o-cresol and m-cresol in urine by use of the kinetic wavelength-pair method.

The kinetic wavelength-pair method was applied to the simultaneous determination of o-cresol and m-cresol, based on their oxidative coupling with aniline in the presence of hypochlorite as oxidant and nitroprusside as catalyst. The benzoquinoneanils produced exhibited severe spectral overlap. Resolution of this isomer mixture by using discrete wavelengths was subject to a high degree of error for the determination of m-cresol since the ratios vo-cresol/vm-cresol (where v denotes initial rate for the oxidative coupling reaction) and epsilon o-cresol/epsilon m-cresol (where epsilon is the absorptivity of reaction products) were greater than unity at any given wavelength. Selectivity in the resolution was achieved by measuring the initial rate difference at the wavelength pair 666-566 nm where the contribution of o-cresol was removed, o-Cresol and m-cresol were simultaneously determined at mass ratios between 5:1 and 1:5 at concentrations from 1 to 5 micrograms ml-1, with relative standard deviations of less than 3%. The proposed method was applied to the determination of o-cresol and m-cresol in urine samples, with analytical recoveries ranging between 95 and 105%.

Aniline Compounds↗
PubMed1995

Multicomponent kinetic determinations using artificial neural networks.

Neural networks were successfully used for multicomponent kinetic determinations of species with rate constant ratios approaching unity without the aid of spectral discrimination. The ensuing method relies on two inputs describing the profile of the kinetic curve for each mixture, which is obtained by preprocessing kinetic data using nonlinear least-squares regression. A straightforward network architecture (2:4s:21) was used to resolve mixtures of 2- and 3-chlorophenol; the trained network estimated the concentrations of both components in the mixture with a relative standard error of prediction of approximately 5%, which is much lower than that obtained with Kalman filtering. The effect of some variables such as the rate constant and analyte concentration ratios on the proposed multicomponent determination is discussed.

Chlorophenols↗
PubMed1995

Kinetic determination of nortriptyline in pharmaceutical samples by use of photometric and fluorimetric detection.

A fast kinetic method is proposed for the photometric and fluorimetric determination of nortriptyline hydrochloride. The method involves measuring the rate of formation of an adduct with 4-chloro-7-nitrobenzofurazan, which exhibits light absorption and fluorescent properties, and the use of a stopped-flow mixing technique, which facilitates application to automatic routine analyses. The reaction rate is measured within only 30 s. The detection limit is 0.12 micrograms ml-1 (photometry) and 0.18 micrograms ml-1 (fluorimetry) and the calibration graph is linear up to 60 micrograms ml-1 in both cases. The precision (as RSD) is less than 1.5%. The proposed method was satisfactorily used for direct analysis of pharmaceutical preparations and a mean recovery near 100% was obtained with both photometric and fluorimetric detection.

Hydrogen-Ion Concentration↗
PubMed1994

Use of the triiodide-cetylpyridinium chloride micellar system for the determination of benzoyl peroxide in pharmaceutical preparations.

A kinetic spectrophotometric method for the determination of benzoyl peroxide in acne preparations is proposed. The method is based on the reduction of benzoyl peroxide by iodide in the cationic micellar medium provided by cetylpyridinium chloride (CPC). The triiodide ion produced associates with CPC micelles, which gives rise to an absorption maximum at 500 nm in addition to substantially increased absorptivity and stability constant for the triiodide complex. Acne preparations can be analyzed directly after dissolution of the samples in ethanol. The detection limit thus achieved is 0.033 microgram.mL-1, so the proposed method surpasses existing alternative methods in sensitivity. The relative standard deviation for 0.25 microgram.mL-1 is 2.1%.

Acne Vulgaris↗
PubMed1994

Improved automatic kinetic method for the determination of various corticosteroids.

Two reaction-rate methods for the determination of corticosteroids at the micromolar level were developed. The methods are modifications of the widely used Blue Tetrazolium and Porter-Silber reactions which are employed for the automatic kinetic determination of corticosteroids using the continuous-addition-of-reagent (CAR) technique. The CAR technique avoided all technical problems typically associated with these reactions such as long incubation at high temperatures, high blank values, and turbidity. On the basis of its analytical figures of merit, the Blue Tetrazolium method was chosen; it allows corticosteroids to be determined at concentrations from 2.7 x 10(-6) to 1.9 x 10(-4) M at a rate of 25 samples/h (triplicate analyses) with an root mean square deviation of ca. 3%. The proposed method was evaluated in recovery experiments and analyses of commercially available formulations.

Adrenal Cortex Hormones↗
PubMed1994

Direct stopped-flow fluorescence polarization immunoassay of abused drugs and their metabolites in urine.

Kinetic methodology was applied to the direct determination of abused drugs (amphetamines, cocaine, and cannabinoids) in urine by stopped-flow fluorescence polarization immunoassay (SF-FPIA). This technique provides analytical data within a few seconds by measuring the variation of polarized fluorescence with time during development of immunochemical reactions. Methods based on this principle are particularly suitable for routine screening of these drugs in urine, being more expeditious than conventional FPIA methods. The dynamic ranges of the calibration curves were 20-300 micrograms/L for d,l-amphetamine, 15-300 micrograms/L for benzoylecgonine (a cocaine metabolite), and 10-400 micrograms/L for 11-nor-delta 8-tetrahydrocannabinol-9-carboxylic acid (a cannabinoid metabolite). The detection limits and within- and between-assay precision were better than those provided by conventional FPIA. Analytical recoveries ranged between 97.5% for d,l-amphetamine and 102.4% for the cannabinoid metabolite. The results for the three analytes were consistent with those obtained by conventional FPIA.

Amphetamine↗
PubMed1993

Kinetic fluorimetric determination of promethazine by a stopped-flow mixing technique.

The oxidation of promethazine to its corresponding fluorescent sulphoxide was used to develop a novel kinetic fluorimetric method for the determination of this drug. The use of a stopped-flow mixing technique makes use of an oxidizing reagent unnecessary because the oxidation is rapidly carried out by dissolved oxygen. The method is simple and fast as it only requires a few seconds to obtain kinetic data which allows ready application to routine analyses. The calibration graph is linear over the range 0.5-80 micrograms ml-1 and the precision (%RSD) is close to 2%. The method was applied to the determination of promethazine hydrochloride in two pharmaceutical preparations.

Chemistry, Pharmaceutical↗
PubMed1993

Stopped-flow photometric determination of clavulanic acid in pharmaceutical and serum samples.

The stopped-flow mixing technique was used to develop a simple, fast kinetic method for the determination of clavulanic acid by reaction with imidazole. Whereas the conventional method requires about 12-15 min for equilibrium to be reached, kinetic measurements can be made within a few seconds. The calibration graph was linear over the range 1-40 microgram ml-1 of clavulanic acid and the detection limit achieved was 0.3 microgram ml-1. The precision and selectivity of the method are reported. The results obtained by applying the proposed method to the analysis of pharmaceutical and serum samples show how easily it can be adapted for routine analyses.

Clavulanic Acid↗