Biomedical subjects

A Santos-Montes

Publications and source records attributed to A Santos-Montes.

10 recordsLinked to original sources

PubMed2005

Comparison of the performance of conventional microparticulates and monolithic reversed-phase columns for liquid chromatography separation of eleven pollutant phenols.

The performance of isocratic separations of 11 pollutant phenols (PP) using monolithic (Chromolith RP-18e) and conventional reversed-phase 5 microm (Luna and Purospher C18) and 4 microm (Synergi C12) particulate size columns, selected from high purity silica materials, has been compared. The separations have been optimized based on a previously optimized separation in which a reversed-phase C18 Luna column and acetonitrile as organic modifier were used, allowing the separation of all phenols tested in 23 min. The optimization process was carried out for each column by studying the effect of the mobile phase (acetonitrile as organic modifier, pH, flow-rate) on phenols separation. Under the optimized separation conditions, all phenols were separated in less than 23 min for all columns tested. Asymmetry factors were further evaluated and used to estimate column efficiency using the Dorsey-Foley equation. The efficiency and asymmetry factors were lower for Chromolith than for Purospher and Luna columns respectively. The Chromolith column was finally selected, due to its lower flow resistance, analysis time and good efficiency and asymmetry factors. The PPs separation was achieved in 3 min. The asymmetry factors were in the range 0.9-1.5 using 50mM acetate buffer (pH = 5.25)-ACN (64:36, v/v) as mobile phase, T=45 degrees C and 4.0 ml min(-1) flow-rate.

Environmental Pollutants↗

PubMed2004

Method development for betamethasone and dexamethasone by micellar liquid chromatography using cetyl trimethyl ammonium bromide and validation in tablets. Application to cocktails.

An isocratic liquid chromatographic method for the determination of betamethasone (BM) and dexamethasone (DM) using methylprednisolone (MPL) as internal standard and micellar mobile phases consisting of cetyl trimethyl ammonium bromide (CTAB) and organic modifiers such as propanol, butanol and pentanol has been developed. The effect of organic modifiers, surfactant concentration, temperature and flow-rate on the separation has been studied. Method validation for dexametasone or bethametasone in tablets was carried out using a mobile phase 0.24% pentanol and 32.5 mM CTAB, a flow-rate of 0.5 ml min(-1), an Hypersil C18 column (60 degrees C), and UV detection at 243 nm. The recoveries for BM and DM found in the accuracy test were 99 +/- 3 and 101 +/- 2, respectively. Repeatability and intermediate precision expressed as R.S.D. were lower than 5% for both compounds. The proposed method was applied to cocktails containing both compounds.

Betamethasone↗

PubMed2000

High-performance liquid chromatographic separation of a complex mixture of diuretics using a micellar mobile phase of sodium dodecyl sulphate. Application to human urine samples.

A systematic optimization of the HPLC separation of a complex mixture containing 19 diuretics by micellar liquid chromatography using sodium dodecyl sulphate (SDS), a Hypersil (150 mmx3.0 mm I.D., 5 microm) C18 column, a flow-rate of 0.5 ml min(-1) and UV absorbance detection has been carried out. Several mobile phases consisting of SDS and organic modifiers such as acetonitrile, tetrahydrofuran, propanol, butanol or pentanol, and the pH adjusted to 3.2, were tested. The effect of the organic modifier and SDS concentration on the retention behavior and separation of the diuretics was investigated. A mobile phase containing 40 mM SDS and 4% tetrahydrofuran was finally selected. Under these conditions, 14 out of 19 diuretics were separated in about 31 min. A bivariant optimization method for the mobile phase SDS-tetrahydrofuran corroborated the above results. The effect of temperature on the retention was also studied, and 50 degrees C was selected. The optimized method was applied to human urine samples of subjects administered Diurex (tablets containing 20 mg of the active ingredient xipamide) without sample preparation.

Calibration↗

PubMed1999

Optimization of separation of a complex mixture of natural and synthetic corticoids by micellar liquid chromatography using sodium dodecyl sulphate. Application to urine samples.

A systematic optimization of the separation of a mixture of corticoids by micellar liquid chromatography, using sodium dodecyl sulphate as surfactant, a Hypersil (250 mm x 3.2 mm I.D.) C18 column, a flow-rate of 0.5 ml min(-1), and UV absorbance detection at 245 nm has been carried out. Several mobile phases consisting of sodium dodecyl sulphate and different organic modifiers were tested of which tetrahydrofuran, PrOH and BuOH were finally selected. On the basis of analysis time, resolution and number of compounds separated, a mobile phase containing 36 mM sodium dodecyl sulphate and 1.91% butanol allowed the separation of thirteen corticoids out of sixteen in about 27 min. Under these conditions the optimal concentration of sodium dodecyl sulphate was found to be 36 mM. A bivariant optimization method for the mobile phase BuOH-sodium dodecyl sulphate corrobored these results. The effects of temperature, ionic strength and flow-rate effect have also been studied. The most important analytical figures of merit were assessed and compared with those obtained using conventional mobile phases. The optimized method was applied to human urine samples of subjects administered with Dezacor (tablets containing 30 mg of the active ingredient deflazacort) with and without sample preparation.

Adrenal Cortex Hormones↗

PubMed1997

The effect of different amines added to eluents as silanol masking agents on the chromatographic behavior of some diuretics in reversed-phase high-performance liquid chromatography using C18 packings.

A preliminary gradient separation in reversed-phase liquid chromatography of a mixture of 25 solutes (diuretics, probenecide, and atenolol) is carried out using several C18 columns and an aqueous phosphoric acid solution (pH 3.2)-acetonitrile mobile phase as a control. Using this separation, the chromatographic behavior of these solutes is studied using 11 water-soluble primary, secondary, and tertiary amine modifiers in the range of 0.7-7.5 mM and a Spherisorb C18 column. This study reveals the presence in the complex sample of two groups of solutes with positive (five typical solutes showed improvements in peak symmetry and retention) or negative responses using these amines as mobile phase modifiers. After experimentation in the presence of amines, these differences are related to solute structure. Hexylamine is found to be an effective masking agent of silanols because of its structure and small required concentration. On these bases, the silanophilic and hydrophobic character of typical solutes and several C18 packings are evaluated under isocratic elution and a relative effectiveness index for amines, and a method for their assessment is proposed. The role of the amine structure on solute retention and the importance of selecting amines of suitable hydrophobic character, molecular geometry, and concentration is discussed. A model of the formation and stabilization of the silanol-amine complex based on hydrophobic and ionic interactions is also proposed.

Amines↗

PubMed1995

Simultaneous determination of cortisol and cortisone in urine by reversed-phase high-performance liquid chromatography. Clinical and doping control applications.

A reversed-phase high-performance liquid chromatography (HPLC) method for the simultaneous determination of cortisol and cortisone in human urine samples using methylprednisolone as the internal standard is described. The method involves the systematic use of isocratic mobile phases of water and methanol, acetonitrile or tetrahydrofuran and a reversed-phase Hypersil C18 column. A water-acetonitrile mixture used as the mobile phase proved to be the most adequate one for analyzing urine samples purified by solvent extraction. The proposed method is sensitive, reproducible and selective. It was applied to the determination of cortisol and cortisone in several human urine samples: healthy subjects, sportsmen before and/or after stress for doping control purposes, and patients with Cushing's syndrome.

Calibration↗

PubMed1994

Extraction and high-performance liquid chromatographic separation of deflazacort and its metabolite 21-hydroxydeflazacort. Application to urine samples.

Two HPLC methods for the separation of a mixture of corticoids including the oxazolinic corticoid deflazacort and its metabolite 21-hydroxydeflazacort using different water-tetrahydrofuran mobile phases were developed. Both separations allowed the detection and determination of fifteen out of sixteen corticoids using different C18 columns. Extraction data for deflazacort and its metabolite using different extraction procedures are also reported. These separation conditions were applied to urine samples from two male volunteers administered Dezacor, with both doping control and clinical purposes.

Adrenal Cortex Hormones↗

PubMed1994

Solvent and solid-phase extraction of natural and synthetic corticoids in human urine.

Optimization of the main variables that affect solvent and solid-phase extraction processes, using disposable C18 cartridges and the non-ionic polymeric resin Serdolit AD-2, of human urine containing natural and synthetic corticoids is described. The data were obtained from different HPLC separations of these compounds using calibration graphs obtained before and after extraction of these compounds. The procedures, including sample preconcentration, showed efficiencies over 90%. NaCl was used to avoid emulsion formation in solvent extraction. The results achieved using solvent and solid-phase extraction are discussed.

Adrenal Cortex Hormones↗

PubMed1993

Optimization of the high-performance liquid chromatrographic separation of a mixture of natural and synthetic corticosteroids.

Systematic optimization of the HPLC separation of a mixture of natural and synthetic corticosteroids was carried out for screening purposes. The method involves binary, ternary or quaternary mixtures containing water, methanol, acetonitrile and tetrahydrofuran. It was possible to separate thirteen out of fourteen corticosteroids contained in a sample in about 26 min, with a 5-microns Hypersil-C18 (250 mm x 4.6 mm I.D.) column thermostated at 30 degrees C, using a mobile phase composed of water-tetrahydrofuran (72:28, v/v). This separation was not improved using other C8 or C18 columns. The effect of temperature on the separation of these compounds was also studied. Calibration graphs were established for each corticosteroid up to 8 micrograms/ml using indapamide as internal standard. The detection limits were in the range 0.02-0.14 ng. The optimized method was applied to urine samples spiked with corticosteroids and showed potential for future applications.

Acetonitriles↗

PubMedDate not supplied

Method development for cortisol and cortisone by micellar liquid chromatography using sodium dodecyl sulphate: application to urine samples of rugby players.

The chromatographic behavior of cortisol and cortisone using a micellar medium of sodium dodecyl sulphate (SDS) as surfactant, a Hypersil C18 (150- x 3.2-mm i.d., 5 microm) column, a flow rate of 0.5 mL/min, and UV absorbance detection at 245 nm is described. The effect of several organic modifiers and the surfactant concentration on the separation is studied. A mobile phase of 18 mM SDS and 8.3% tetrahydrofuran allows for the separation of cortisol and cortisone up to baseline. These results are also achieved by applying a bivariant optimization method. The proposed method is sensitive, reproducible, and selective. In addition, it is less expensive than conventional high-performance liquid chromatography methods for cortisol and cortisone. The method is applied to the determination of cortisol and cortisone in urine samples of rugby players before and after stress for doping control purposes.

Chromatography, Liquid↗