Biomedical subjects

V Tomás

Publications and source records attributed to V Tomás.

At least 19 recordsLinked to original sources

PubMed2003

Spectrofluorimetric determination of formaldehyde by a flow-injection method based on its catalytic effect on the acridine yellow-bromate reaction.

A flow-injection configuration for the determination of formaldehyde is proposed. The method is based on the enhancing effect of formaldehyde on the oxidation of acridine yellow by bromate in acidic medium. The proposed procedure is simple, inexpensive, sensitive and suitable for concentrations of formaldehyde between 1 and 56 microg mL(-1). A sampling-rate of 60 samples h(-1) was achieved. The effect of several organic and inorganic species was studied. The method was applied to the determination of formaldehyde in pharmaceuticals, milk and air in work environments. The accuracy of the method was confirmed by comparing the results with those obtained using the standard acetylacetone method.

Air Pollutants↗

PubMed2002

Direct determination of ranitidine and famotidine by CE in serum, urine and pharmaceutical formulations.

A simple and sensitive capillary electrophoresis method using UV detection has been developed for the direct determination of ranitidine (RANT) and famotidine (FAMT) in serum, urine and pharmaceutical formulations. A buffer consisting of 60 mM phosphate buffer adjusted to pH 6.5 was found to provide a very efficient and stable electrophoretic system for the analysis of both drugs. The detection limits obtained were 0.088 microgram ml(-1) for RANT and 0.16 microgram ml(-1) for FAMT.

Chemistry, Pharmaceutical↗

PubMed2001

Flow-injection extraction-spectrophotometric method for the determination of ranitidine in pharmaceutical preparations.

The spectrophotometric determination of trace amounts of ranitidine was carried out by liquid-liquid extraction using bromothymol blue with a flow system. The determination of ranitidine in the range of 1 x 10(-5) - 1 x 10(-4) mol l(-1) was possible with a sampling frequency of 40 samples h(-1). The method was satisfactorily applied to the determination of ranitidine in pharmaceutical preparations and the recovery was quantitative and no interferences from excipients were observed.

Anti-Ulcer Agents↗

PubMed2001

Fluorimetric determination of total ascorbic acid by a stopped-flow mixing technique.

A simple, rapid and automatic fluorimetric method for the determination of total ascorbic acid is described. The method makes use of the stopped-flow mixing technique in order to achieve the rapid oxidation of ascorbic acid by dissolved oxygen to dehydroascorbic acid, which then reacts with o-phenylenediamine to form a fluorescent quinoxaline. The initial rate and fluorescence signal of this system are directly proportional to the ascorbic acid concentration. The calibration graph was linear over the range 0.1-30 microg ml(-1) (kinetic method) and 0.25-34 microg ml(-1) (equilibrium method). The precision (% RSD) was close to 0.5%. The method has been used for the determination of ascorbic acid in pharmaceutical formulations, fruit juices, soft drinks and blood serum.

Ascorbic Acid↗

PubMed2000

Determination of proteins in serum by fluorescence quenching of rose bengal using the stopped-flow mixing technique.

The stopped-flow mixing technique was used to develop a very fast, sensitive and accurate method for determining total proteins. The method is based on the lower fluorescence of Rose Bengal caused by binding of the dye to the proteins. The decrease in the fluorescence intensity, measured at 572 nm with excitation 555 nm, was linearly related to protein concentration from 1.3 to 24.5 micrograms ml-1. The detection limit was 0.3 microgram ml-1. The method was satisfactorily applied to the determination of total proteins in different serum samples.

Animals↗

PubMed2000

Sensitive determination of diquat by a kinetic method using the stopped-flow mixing technique.

A simple, sensitive, selective, fast and inexpensive assay for the determination of diquat is proposed. The method is based on the reduction of the herbicide to a strongly fluorescent monocation radical with sodium dithionite. The initial rate of this reaction is directly proportional to the diquat concentration. The stopped-flow mixing technique was used because the kinetic data can be obtained in only 7 s, meaning that the method can be automated. The calibration graph is linear over the range 5-500 ng ml-1 and the precision (RSD) is close to 1.2%. The applicability of the method was demonstrated by determining the herbicide in different kinds of samples.

Diquat↗

PubMed1999

Flow injection determination of vitamin K3 by a photoinduced chemiluminescent reaction.

The determination of vitamin K3 using the coupling between a photochemical reaction and a chemiluminescent reaction in a flow system is described. The method is based on the photooxidation of ethanol sensitized by vitamin K3 to yield hydrogen peroxide, which is monitored through the chemiluminescent reaction with luminol catalysed by hematin. The new approach allows the determination of vitamin K3 in a wide concentration range (1 x 10(-7)-5 x 10(-4) mol l-1) with a throughput of 30 samples h-1. The applicability of the method was demonstrated by the determination of vitamin K3 in pharmaceutical preparations.

Flow Injection Analysis↗

PubMed1999

Flow injection determination of lactate based on a photochemical reaction using photometric and chemiluminescence detection.

A photochemical method for the determination of lactate using a flow-injection system is proposed. The method is based on the decomposition of lactate in the presence of UO2(2+) and Fe3+ upon irradiation with UV or visible light. The Fe2+ produced in the photochemical process was monitored by measuring the absorbance after complexation with ferrozine (lambda max = 562 nm) or the chemiluminescence (CL) intensity in a luminol system without added oxidant. The range of measurements depended on the length of the irradiation time and the detection system used. The detection limits using CL and photometric detection were 2 ng ml-1 and 50 ng ml-1, respectively. The sample throughput was 45 samples h-1. The usefulness of the method was demonstrated by determining lactate levels in blood serum, milk, yoghurt, beer and pharmaceutical preparations.

Animals↗

PubMed1998

Selective determination of naproxen in the presence of nonsteroidal anti-inflammatory drugs in serum and urine samples using room temperature liquid phosphorimetry.

A very simple, rapid and highly sensitive method is described for determining naproxen in serum and urine. This method is based on room temperature phosphorescence of naproxen in sodium dodecylsulphate micelles, with thallium(I) providing the external heavy atom and sodium sulphite acting as the oxygen scavenger. Under the optimum and experimental conditions, the range of application is 0.09-4.5 micrograms ml-1 and the limit of detection is 0.03 micrograms ml-1. The most relevant characteristic of this method is its great selectivity, e.g. naproxen can be determined in the presence of other nonsteroidal anti-inflammatory drugs (NSAIDs). The clinical applicability of this procedure has been tested, analysing naproxen in serum and urine samples. The analytical recoveries and inter- and intra assay precision data obtained demonstrate the usefulness of this procedure when used with very complex samples.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1998

Spectrofluorimetric determination of paraquat by manual and flow injection methods.

The reaction involving the formation of a fluorescent charge-transfer complex between paraquat and benzaldehyde was studied in ethanol-water medium. In the presence of a large excess of benzaldehyde, the fluorescence intensity is linearly related to paraquat concentration from 0.13 to 7.4 micrograms ml-1. The method can be easily adapted to a flow system using a two-channel manifold, the peak height being proportional to the paraquat concentration over the range 1.6-22.3 micrograms ml-1. Manual and flow-injection procedures were satisfactorily applied to the determination of paraquat in commercial herbicides, waters, soils and potatoes.

Benzaldehydes↗

PubMed1997

Flow injection fluorimetric determination of ascorbic acid based on its photooxidation by thionine blue.

The photooxidation of ascorbic acid sensitized by Thionine Blue was studied. The Leucothionine Blue formed during the reaction is highly fluorescent. A flow injection method using merging zones is proposed for the determination of ascorbic acid over a concentration range from 8 x 10(-7) to 5 x 10(-5) mol l-1 with a throughout of 80 samples per h. The method was used for the simple and rapid determination of ascorbic acid in pharmaceuticals, fruit juices and soft drinks.

Ascorbic Acid↗

PubMed1997

Determination of norfloxacin in real samples by different spectrofluorimetric techniques.

Simple, rapid, accurate and sensitive spectrofluorimetric methods for the determination of norfloxacin are described. The methods are based on the reaction of this drug with aluminium(III) ion to form a strongly fluorescent complex. Fluorescence properties of the AlIII-norfloxacin complex were used for the determination of this drug in pharmaceutical preparations. First-derivative constant wavelength synchronous fluorescence spectrometry was used for the determination of norfloxacin in the presence of nalidixic acid. The determination of norfloxacin in urine without the need of tedious pre-separation was achieved by using zero-crossing second-derivative synchronous fluorescence spectrometry.

Aluminum↗

PubMed1996

Fluorimetric determination of chloroxine using manual and flow-injection methods.

A reliable and highly sensitive method is described for the determination of chloroxine in pharmaceutical preparations. It involves the formation of a complex between chloroxine and aluminum(III) in a micellar medium. The complex is a very fluorescent species, and there is a linear relationship between chloroxine concentration and fluorescence intensity over the range 2.0 x 10(-8)-5.1 x 10(-5) mol l-1. The limit of detection is 5 x 10(-9) mol l-1. The method can be easily adapted to a flow system using a three-channel manifold, the peak height being proportional to the chloroxine concentration over the range 5.6 x 10(-7)-5.6 x 10(-5) mol l-1. Manual and flow-injection procedures permit the determination of chloroxine in the presence of chlorquinaldol, and have been successfully applied to the determination of chloroxine in pharmaceutical preparations.

Aluminum↗

PubMed1996

Flow-injection fluorimetric determination of penicillamine and tiopronin in pharmaceutical preparations.

Two flow-injection methods for the fluorimetric determination of penicillamine and tiopronin are proposed. The procedures are based on the oxidation of these drugs by thallium(III). In hydrochloric acid medium the fluorescence of thallium(I) formed in the oxidation of penicillamine or tiopronin is monitored using excitation and emission wavelengths of lambda ex = 227 nm and lambda em = 419 nm respectively. Linear calibration graphs were obtained between 3 x 10(-7) and 8 x 10(-6) M for penicillamine and between 8 x 10(-7) and 2 x 10(-5) M for tiopronin with sampling frequencies of 90 and 45 samples h-1 respectively. The relative standard deviations were in the ranges 0.48-0.29% for penicillamine and 1.04-0.31% for tiopronin. The applicability of the method to the determination of both drugs in pharmaceutical preparations was demonstrated by investigating the effect of potential interferences and by analysis of commercial preparations.

Capsules↗

PubMed1994

Flow-injection determination of Novalgin using amperometric detection at a glassy carbon electrode.

An electroanalytical study of the oxidation of Novalgin (dipyrone) at a glassy carbon electrode in aqueous solution has been carried out. A flow-injection method with amperometric detection based on this oxidation process is also described. The influence of flow rate, coil length and injection volume on the sensitivity of the method was established. The calibration graph was linear within the range 3 x 10(-6)-3 x 10(-5) M in an ammonia buffer solution (pH 9) as a potential of 0.4 V versus an Ag/AgCl reference electrode. The sampling rate was 54 samples h-1. The applicability of the method to the determination of Novalgin in pharmaceutical preparations was demonstrated by investigating the effect of potential sources of interference and by analysing commercial preparations.

Biosensing Techniques↗

PubMed1993

Extraction-spectrofluorimetric method for the determination of erythromycin and its esters in pharmaceutical formulations using manual and flow-injection procedures.

A sensitive and rapid extraction-spectrofluorimetric method for the determination of erythromycin, based on the formation of an ion pair with Erythrosine B, is described. The calibration graph resulting from the measurement of the fluorescence of the chloroform extract (10 cm3) at 560 nm with excitation at 544 nm is linear over the range 10-600 micrograms of erythromycin per 20 cm3 of total volume of aqueous phase, with a relative standard deviation (RSD) of 1.5% for 3.7 micrograms cm-3 erythromycin. The method can be successfully adapted to an unsegmented flow system, the peak height being proportional to erythromycin concentration over the range 0.65-5.88 micrograms of erythromycin per 400 mm3 of sample solution injected. Up to 45 samples h-1 can be processed with an RSD of 2.9-3.8%. Manual and flow-injection methods were satisfactorily applied to the determination of erythromycin in pharmaceutical preparations.

Erythromycin↗

PubMed1992

Spectrofluorimetric flow injection method for the individual and successive determination of L-cysteine and L-cystine in pharmaceutical and urine samples.

A flow injection configuration is proposed for the determination of L-cysteine and L-cystine individually and for mixtures of both analytes. The procedure is based on the rapid oxidation of L-cysteine by thallium(III) with concomitant formation of fluorescent thallium(I). The inclusion of a selecting valve and of a copper-coated cadmium column in the configuration allows the successive determination of two analytes. Linear calibration graphs were obtained between 5 x 10(-6) and 5 x 10(-5) mol dm-3 of L-cysteine and between 2 x 10(-6) and 2 x 10(-5) mol dm-3 of L-cystine. The applicability of the method to the determination of L-cysteine and L-cystine in pharmaceutical preparations was demonstrated by investigating the effect of potential interferents and by the analysis of commercial preparations. The method was successfully applied to the determination of L-cysteine and L-cystine in urine samples.

Cysteine↗

PubMed1991

A simple photokinetic method for the determination of nitroprusside in biological and pharmaceutical samples.

A simple method has been developed for the determination of nitroprusside in human serum and pharmaceutical preparations. The new method is based on the strong inhibitory effect of nitroprusside on the photochemical reduction of phloxin by ethylenediaminetetra-acetic acid. The rate measurements are accomplished very simply by measuring the time needed for the absorbance to be reduced to 1/10th of its initial value. Optimal conditions for the determination of nitroprusside at concentrations of 15-200 ng ml-1 are described.

Edetic Acid↗