Biomedical subjects

L Toribio

Publications and source records attributed to L Toribio.

28 records · Page 2Linked to original sources

PubMed2000

Determination of the 2-bromomethyl-2-(2,4-dichlorophenyl)-1, 3-dioxolan-4-yl)methyl benzoate diastereoisomers by supercritical fluid chromatography.

The study of the separation and determination of the two 2-bromomethyl-2-(2,4-dichlorophenyl)-1,3-dioxolan-4-yl-methyl benzoate diastereoisomers is presented in this work. The separation was achieved using packed column supercritical fluid chromatography. Three stationary phases were checked, the C(18) packing providing the best results. The influence of several parameters (nature and percentage of modifier, temperature and pressure) on the separation were also evaluated. The baseline separation (R(s)=1.78) of the compounds was obtained in only 2 min, using a C(18) column, a pressure of 100 bar, a temperature of 35 degrees C, a flow-rate of 2. 5 ml/min and 5% of 2-propanol as organic modifier. Under these conditions the unwanted diastereoisomer (trans) was eluted before the main compound (cis), so the determination of the purity was more accurate.

2-Propanol↗

PubMed2000

Separation of ketoconazole enantiomers by chiral subcritical-fluid chromatography.

The separation of ketoconazole enantiomers by subcritical-fluid chromatography using an amylose-based column is described. Drastic changes in the resolution have been obtained for the different organic modifiers evaluated, with ethanol providing the best results. Other chromatographic parameters such as temperature, pressure and flow-rate have also been studied. The best results in terms of resolution and analysis time were obtained using 30% ethanol (containing 0.1% triethylamine and 0.1% trifluoroacetic acid), a pressure of 300 bar, a temperature of 35 degrees C and a flow-rate of 3 ml/min. Under these conditions the ketoconazole enantiomers are resolved in a short time (less than 7 min) and with high resolution (4.29).

Amylose↗

PubMed2000

Chiral separation of four 1,3-dioxolane derivatives by supercritical fluid chromatography on an amylose-based column.

The chiral separation of four 1,3-dioxolane derivatives by supercritical fluid chromatography on an amylose-based column is described. The effects of mobile phase composition, temperature and pressure have been investigated. The nature of the modifier is the parameter which has the highest impact on the chiral resolution and it is more important than the polarity of the mobile phase. The organic modifier used for the best enantiomeric separation was different for each compound, because it depends strongly on the molecular structure of the compound.

Amylose↗

PubMed2000

Validation of the removal of acetylsalicylic acid. Recovery and determination of residues on various surfaces by high performance liquid chromatographic.

The validation of a procedure to clean glass, vinyl and stainless steel surfaces that have been exposed to acetylsalicylic acid during its manufacture is described. The cleaning procedure using two cotton swabs moistened with the mobile phase was validated using a wipe-test and a high-performance liquid chromatography (HPLC) method developed to determine low quantities of the acid. The HPLC method involves an octadecylsilane column at 55 degrees C, a mixture of water-acetonitrile-orthophosphoric acid (779:220:1, v/v) as mobile phase and detection at 226 nm. Recoveries of 86%, 90% and 94% were obtained from vinyl, glass and stainless steel plates respectively. The validation gave acceptable levels of sensitivity, recovery, precision and linearity.

Aspirin↗

PubMed1998

Gas chromatography with electron-capture and nitrogen-phosphorus detection in the analysis of pesticides in honey after elution from a Florisil column. Influence of the honey matrix on the quantitative results.

A modified procedure to extract pesticides from honey samples that involves loading the honey onto a Florisil packed column and subsequently eluting it with an n-hexane-dichloromethane mixture is proposed. Anomalous high gas chromatographic responses and subsequently very high recoveries for the pesticides in the extracts were obtained by a conventional calibration with pesticide solutions in organic solvent. This effect was attributed to the honey matrix and can be circumvented by using spiked honey extracts as calibration standards.

Chromatography, Gas↗

PubMed1998

Packed-column supercritical fluid chromatography coupled with solid-phase extraction for the determination of organic microcontaminants in water.

A multiresidue method for the analysis of 35 common contaminants (including pesticides, polycyclic aromatic hydrocarbons and phenols) in lough and river waters from Castilla y León Spanish region, by using supercritical fluid chromatography (SFC) with five silica packed columns, is described. In order to decrease the detection limits, a preconcentration step by coupling solid-phase extraction to the SFC system was used. The different variables affecting the extraction procedure were studied and optimized, selecting the Isolute Env+ as the best sorbent. The detection limits achieved ranged from 0.4 to 2.6 micrograms l-1.

Chromatography↗

PubMed1997

High-performance liquid chromatographic determination of benomyl and carbendazim residues in apiarian samples.

Simple procedures for the extraction and chromatographic determination of benomyl and carbendazim in honey, bees wax, larvae, bees and pollen are proposed. The fungicides were extracted from honey, larvae and bees using ethyl acetate, while methanol was more suitable for wax and pollen samples. Pollen extracts need a further clean-up step with n-hexane. The determination is carried out by reversed-phase high-performance liquid chromatography (HPLC) with fluorescence detection. The procedures have been applied to the analysis of benomyl on honey and larvae samples from hives whose bees were nourished with artificial food mixed with benomyl.

Animals↗

PubMed1997

Determination of polycyclic aromatic hydrocarbons in waters by use of supercritical fluid chromatography coupled on-line to solid-phase extraction with disks.

The potential of supercritical fluid chromatography (SFC) coupled on-line to solid-phase extraction (SPE) with disks for determining sixteen different polycyclic aromatic hydrocarbons (PAHs) was assessed. A preliminary study of the chromatographic separation was conducted that led to the use of SPE coupled to SFC for improved detection limits. Disks of two different materials, i.e., C18 and polystyrene-divinylbenzene, were assayed in terms of the variables influencing the extraction step. C18 disks provided the best results, with detection limits ranging from 0.1 to 1.5 micrograms l-1. The ensuing method was applied to river and tap water with good repeatability and reproducibility, and no interference from the sample matrix.

Chromatography, Liquid↗

PubMed1997

Determination of glutathione, cysteine and N-acetylcysteine in rabbit eye tissues using high-performance liquid chromatography and post-column derivatization with 5,5'-dithiobis(2-nitrobenzoic acid).

A high-performance liquid chromatographic method to determine glutathione, cysteine and N-acetylcysteine in rabbit retina, vitreous and lens has been developed. The thiols are separated using a 25 x 0.46-cm octadecylsilane column with 0.5 M phosphate buffer, pH 3, as mobile phase. The detection, at 412 nm, involves a post-column derivatization with 5,5-dithiobis(2-nitrobenzoic acid) in presence of cationic micelles of hexadecyltrimethylammonium bromide that enhances the sensitivity. The detection limits are 0.21, 0.92 and 0.61 mumol/g wet sample for glutathione, cysteine and N-acetylcysteine, respectively.

Acetylcysteine↗

PubMed1996

On-line solid-phase extraction coupled to supercritical fluid chromatography to determine phenol and nitrophenols in water.

Determining of phenol and nitrophenols using solid-phase extraction on-line coupled to supercritical fluid chromatography (SFC) is studied. SFC quickly separated the compounds studied, in less than 6 min, and solid-phase extraction was used to decrease the limits of detection. C18, PLRP-S and a highly cross-linked styrene-divinylbenzene copolymer in a 10 x 3 mm I.D. laboratory-packed precolumn were tested comparatively as sorbents in the preconcentration step. Tetrabutylammonium bromide was used as ion-pair reagent in the extraction process to increase breakthrough volumes, mainly for phenol. Performance of the method was checked with tap and river waters.

Chromatography, High Pressure Liquid↗