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Biomedical subjects

M Valcárcel

Publications and source records attributed to M Valcárcel.

At least 73 records · Page 4Linked to original sources
PubMed1994

Sequential determination of triglycerides and free fatty acids in biological fluids by use of a continuous pretreatment module coupled to a gas chromatograph.

A continuous system coupled to a gas-liquid chromatograph was used for the sequential determination of triglycerides and free fatty acids in serum and urine. The module provides compositional information and hence more detailed information on lipid metabolism changes in patients suffering metabolic disorders. Lipids in biological samples are manually extracted in methanol-n-hexane and introduced into the flow system; free fatty acids are then separated by retention on an ion-exchange resin and triglycerides (not retained) are transesterified with acetyl chloride in methanol. The resulting methyl esters are continuously injected into the gas chromatograph and determined by using a flame ionization detector. In a second step, retained free fatty acids are eluted and derivatized (also with acetyl chloride in methanol) and subsequently determined similarly as the triglycerides. The proposed method was applied to the determination of triglycerides in a lipid control serum; free fatty acids were determined in a human pool serum by the proposed method and compared with the volumetric method used in clinical practice. The results obtained in both instances showed good agreement between the results provided for triglycerides and free fatty acids. The proposed method was also applied to urine samples; a parallel recovery study was also made in order to assess the performance of the method.

Automation↗
PubMed1994

Flow-through photometric sensor for determination of sulfonamides.

A sensor based on integration of spectrophotometric detection and retention of the product of the Bratton-Marshall reaction for the determination of sulfanilamide, sulfamethazine, sulfaquinoxaline and sulfathiazole is reported. The methods developed using this sensor in a flow injection manifold feature linear ranges for these analytes between 10 and 1200 ng ml(-1) with relative standard deviations smaller than 2.6% in all instances and they were applied to the determination of sulfonamides in spiked milk and water samples with excellent results. The two main advantages of these sensor-based methods over other automated and non-automated counterparts are enhanced sensitivity as a result of in situ concentration and avoidance of using a de-bubbler to eliminate the nitrogen produced in the flowing system.

Animals↗
PubMed1994

Direct analysis of milk for aluminium using electrothermal atomic absorption spectrometry.

This work was conducted in order to develop a sensitive, precise method for the direct determination of aluminium in dairy products without sample pre-treatment. For this purpose, various chemical modifiers and thermal programmes for an electrothermal atomic absorption spectrometer were assessed. Different dry and wet sample pre-treatments were investigated in order to test the applicability of the method to the direct determination of aluminium in the matrices. Aluminium adsorption or leaching in various milk storage materials was also investigated. The proposed method allows the determination of aluminium in the range 5-50 micrograms l-1 and a detection limit of 0.32 micrograms l-1 for aluminium. The precision achieved, expressed as the relative standard deviation, was 5.6% for within-run assays (repeatability) and 12.7% for between-run assays (reproducibility). Various types of commercially available milk (skim, low fat and whole) and milkshake (marketed in different packages) were analysed after dilution to 1 + 3 (v/v) with 0.2% HNO3. Processing whole milk for drinking slightly decreases its aluminium content, but heating in aluminium vessels also slightly increases its content. The reliability of the entire procedure was confirmed by an analysis performed on a Standard Reference Material.

Aluminum↗
PubMed1993

Automatic gas chromatographic determination of N-methylcarbamates in milk with electron capture detection.

A new analytical method that combines on-line derivatization-extraction and gas-liquid chromatography for the determination of N-methylcarbamates is reported. The hydrolysis products of N-methylcarbamates (phenols) are derivatized and extracted in a continuous fashion using pentafluoropropionic anhydride (derivatizing reagent) in n-hexane as an extractant. The thermal instability of N-methylcarbamates is overcome by forming fluoro derivatives that can be identified and quantified at the nanogram per milliliter level with an ECD detector. Application of the proposed method to six mixtures of N-methylcarbamates yielded detection limits between 2 and 20 ng/mL and a relative standard deviation of 2.35-3.70%. Average recoveries of N-methylcarbamates added to cow's milk at concentrations between 50 ng/mL and 2 micrograms/mL ranged from 93.7 to 100.8%.

Acylation↗
PubMed1993

Automated determination of peroxides in olive oil by flow injection.

A method for the determination of the peroxide value of olive oil based on flow injection principles is proposed. The method requires no pre-treatment of samples that have undergone natural or forced oxidation as the sensitivity can be accommodated over wide margins (determination range 3.4-537 mequiv kg-1). The precision of the method, expressed as relative standard deviation, ranges from 0.7 to 2.4% and the sampling frequency is 15 h-1.

Flow Injection Analysis↗
PubMed1993

Automated enzymatic determination of sodium in serum.

An automated method based on the principles of flow-injection analysis is proposed for the enzymatic determination of sodium ion in serum. The method relies on the activation of beta-galactosidase by the analyte. The features of the proposed method include linear range between 1 and 1700 mumol/L, a sampling rate of 50 samples/h, a sample volume of 50 microL, and the absence of interferences from species usually present in serum. The results obtained were consistent with those provided by widely used methods such as those based on flame spectrometry and direct potentiometry with ion-selective electrodes.

Flow Injection Analysis↗
PubMed1992

Diagnostic exposure in a primary care clinic during pediatric training.

A retrospective and descriptive study was done in a general pediatric training site with the purpose of identifying the diagnoses to which the trainees have been exposed, as well as the changes in the pattern of these diagnoses. The number of patient-doctor contacts, type of patient visit, and frequency of diagnoses were compared. A total of 66,054 patient-doctor contacts occurred during the years 1979 to 1989, comprising 79.6 percent scheduled health visits and 20.4 percent emergency visits. The main diagnoses were: healthy child/adolescent (HV), well baby (WB), upper respiratory infection, skin diseases, bronchial asthma, acute gastroenteritis, otitis media, anemia, incomplete immunization, psychosocial problems, nutritional/linear growth problems, psychosomatic disturbances, parasitosis, and pneumonia. There was a significant decrease (P < .005) in the diagnosis of infectious diseases and a significant increase (P < .005) in the proportion of WB and HV. The latter were the two most common diagnoses in the year 1989.

Acute Disease↗
PubMed1990

Gas chromatographic determination of phenol compounds with automatic extraction and derivatization.

Two gas chromatographic procedures for the determination of a variety of substituted phenols in water samples are described. The phenols were extracted or extracted-derivatized by using a continuous liquid-liquid extraction-derivatization system and quantified with flame ionization detection. Ethyl acetate was found to be the most efficient solvent for phenols whereas n-hexane yielded essentially the same recoveries for derivatized phenols. Between 0.1 and 300 mg/l of the different phenols can be detected with a relative standard deviation 1.1 and 3.7%. The acetate esters of six phenols were formed by the direct addition of acetic anhydride to the organic extractant. The stable acetate esters thus formed were isolated by using a standard dimethyl polysiloxane gas chromatographic column.

Chlorophenols↗
PubMed1990

Determination of alanine aminotransferase in human serum in an open-closed flow injection configuration.

Open-closed flow injection systems allow the development of methods based on multidetection by using conventional detectors. The methods proposed here for the determination of alanine aminotransferase (ALT) utilize a photometric detector included in the closed circuit, which allows one to perform fixed-time and reaction-rate measurements whose sensitivity can be increased by using the sum of the analytical signals. The methods, with determination ranges between 1 and 500 U l-1 of ALT, feature sampling frequencies up to 60 h-1. Their application to serum samples provided excellent results, with recoveries between 95 and 106% and averaging at 99.9%.

Alanine Transaminase↗
PubMed1990

Automation of pharmaceutical dissolution testing by flow injection analysis.

The different types of instruments used for monitoring pharmaceutical dissolution testing are presented. Their features and the need for automation are critically discussed. The advantages of flow injection analysis in this respect are illustrated by a variety of examples clearly showing its adaptability to the different problems posed by other automatic and non-automatic alternatives.

Autoanalysis↗
PubMed1990

Indirect continuous automatic determination of pharmaceuticals by atomic absorption spectroscopy.

The implementation of continuous separation techniques such as precipitation, liquid-liquid and solid-liquid extraction in FIA manifolds coupled on-line with an atomic absorption spectrometer for the determination of active components (sulphonamides, local anaesthetics, amphetamines, benzodiazepines, chloramphenicol and methadone) in pharmaceuticals and biological fluids is systematically described. The basic features of the analytical methodologies described (sensitivity, selectivity, precision and rapidity) are also discussed and critically compared.

Amphetamines↗
PubMed1990

Use of photochemical reactions in flow injection: determination of oxalate in urine.

The use of photochemical reactions in flow injection (FI) is reported. The irradiation of an FI reactor with a suitable source facilitates the development of the iron(III)-oxalate reaction, allowing the amperometric determination of the anion in the range 1.0-13.0 micrograms ml-1, with a relative standard deviation of 1.1% and a sampling frequency of 40 h-1. The proposed method was applied successfully to the determination of oxalate in urine samples.

Humans↗
PubMed1989

Flow injection analysis of pharmaceuticals.

An overview of the most representative problems solved by flow injection analysis (FIA) in drug analysis is presented. Different aspects of this technique which can be manipulated with specific purposes are discussed and special emphasis is placed on the possibilities of FIA in dissolution test control.

Chemistry, Pharmaceutical↗
PubMed1987

Determination of total cholesterol in serum by flow injection analysis with immobilized enzymes.

Several photometric and fluorimetric methods are proposed for the determination of cholesterol by use of enzymes immobilized on controlled-pore glass and the normal and stopped-flow injection modes, achieving linear ranges of the calibration curves between 26-776 mumol/l and 5-265 mumol/l with excellent regression coefficients and good coefficients of variation. The methods have been applied to the determination of this analyte in serum with excellent results.

Cholesterol↗