Biomedical subjects

R Izquierdo-Hornillos

Publications and source records attributed to R Izquierdo-Hornillos.

At least 19 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↗

PubMed2005

HPLC method development for testosterone propionate and cipionate in oil-based injectables.

Two isocratic liquid chromatographic methods for the determination of testosterone propionate (TP) and cipionate (TC) in oil-based injectables using methyltestosterone and bolasterone as internal standards, respectively, have been developed and validated. Mobile phases 57% water:acetonitrile 43% (v:v) and 54% water:acetonitrile 46% (v:v) were used for TP and TC, respectively. For both methods, a bonded-silica Luna CN (250 mm x 4.6 mm i.d., 5 microm) (25 degrees C) column, a flow-rate 1 ml min(-1) and UV absorbance detection at 245 nm were used and two separations up to base line were achieved. Prior to HPLC analysis, sample preparation was required, including extraction of TP and TC from oil-based injectables using the surfactant sodium dodecyl sulphate.

Chromatography, High Pressure Liquid↗

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↗

PubMed2003

Optimization of the separation of a complex mixture of natural and synthetic anabolic steroids by micellar liquid chromatography.

A systematic optimization of the HPLC separation of a complex mixture containing natural and synthetic anabolic steroids by micellar liquid chromatography using a Hypersil (150 mm x 3.0 mm i.d., 5 microm) C18 column and UV detection at 245 nm (exception is made for oxymetolone and danazol which were monitorized at 280 nm) has been carried out. The isocratic micellar mobile phases (from binary to quaternary) consisted of sodium dodecyl sulphate and organic modifiers such as acetonitrile, tetrahydrofuran, propanol, butanol or pentanol. The effect of the organic modifiers, surfactant concentration, temperature, ionic strength and flow-rate on the separation has been studied. A micellar mobile phase 5% propanol and 40 mM surfactant allowed the separation of 12 steroids out of 14 tested in about 20 min. A bivariant optimization method for the micellar mobile phase propanol-surfactant corroborated the above results.

Anabolic Agents↗

PubMed2003

Method development for corticosteroids and anabolic steroids by micellar liquid chromatography.

A systematic optimization of the HPLC separation of a complex mixture containing urinary steroids (anabolics and corticoids), boldenone and bolasterone (synthetic anabolics) by micellar liquid chromatography has been carried out. The isocratic micellar mobile phases (from binary to quaternary) consisted of sodium dodecyl sulphate and organic modifiers such as acetonitrile, tetrahydrofuran, propanol, butanol or pentanol. The effect of the organic modifiers, surfactant concentration, temperature, ionic strength and flow-rate on the separation has been studied. A micellar mobile phase made of 5% propanol and 40 mM surfactant allowed the separation of 13 steroids in about 23 min. A bivariant optimization method for the micellar mobile phase surfactant-propanol corroborated the above results. The separations obtained show good perspectives for future developments.

Adrenal Cortex Hormones↗

PubMed2003

Conventional and micellar liquid chromatography method development for danazol and validation in capsules.

Two isocratic liquid chromatographic methods (conventional and micellar) for the determination of danazol (DZ) in capsules using canrenone (CAN) as internal standard have been developed and validated. In conventional liquid chromatography a mobile phase 35% water:acetonitrile 65%, v:v, a flow-rate 1 ml min(-1) and a C18 Hypersil ODS (250 x 4.6 mm, 5 microm) column (25 degrees C) were used. In micellar liquid chromatography (MLC) the conditions were: mobile phase 40 mM sodium dodecyl sulfate:2% pentanol, flow-rate 0.5 ml min(-1) and C18 Hypersil ODS (150 x 3.0 mm, 5 microm) column (60 degrees C). For both methods. UV absorbance detection at 280 nm was used and a separation up to base line was achieved. Prior to HPLC analysis a simple sample preparation was required. The recoveries found in the accuracy test were 99 +/- 10 and 101 +/- 8%, in conventional liquid chromatography (CLC) and MLC, respectively. Repeatability and intermediate precision expressed as R.S.D. were lower than 5% for both methods. Detection limits obtained were 2.4 and 3.0 ng g(-1) in CLC and CLM, respectively.

Canrenone↗

PubMed2003

Optimization and validation of conventional and micellar LC methods for the analysis of methyltestosterone in sugar-coated pills.

Two isocratic liquid chromatographic methods (conventional and micellar) for the determination of methyltestosterone in sugar-coated pills using fluoxymesterone as internal standard have been developed and validated. In conventional liquid chromatography a mobile phase 45% water:acetonitrile 55% (v:v), a flow-rate 1 mlmin(-1) and a C(18) Hypersil ODS (250 x 4.6 mm, 5 microm) column (25 degrees C) were used. In micellar liquid chromatography the conditions were: mobile phase 40 mM sodium dodecyl sulfate: 10% propanol, flow-rate 0.5 mlmin(-1) and C(18) Hypersil ODS (150 x 3.0 mm, 5 microm) column (60 degrees C). For both methods, UV absorbance detection at 245 nm was used and a separation up to base line was achieved. Prior to HPLC analysis a simple sample preparation was required.

Anabolic Agents↗

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↗

PubMed2000

High-performance liquid chromatographic optimization study for the separation of natural and synthetic anabolic steroids. Application to urine and pharmaceutical samples.

An HPLC separation of a complex mixture containing 14 androgenic anabolic steroids (natural and synthetic) for screening purposes has been carried out. The applied optimization method involved the use of binary, ternary and quaternary mobile phases containing acetonitrile, methanol or tetrahydrofuran as organic modifiers. The effect of different reversed-phase packings and temperature on the separation using acetonitrile as organic modifier was studied. The optimum separation was achieved by using a water-acetonitrile (55:45, v:v) mobile phase and a Hypersil ODS (250 mm x 4.6 mm) 5 microm column (30 degrees C) in about 38 min, allowing the separation of 14 out of 14 compounds tested (when danazol is excluded, 13 out of 14 were separated in 23 min). Calibration graphs were obtained using bolasterone, methyltestosterone and canrenone as internal standards. Detection limits were in the range 0.012-0.11 microg ml(-1). The optimized separation was applied for monitoring the norethindrone acetate hydrolysis from tablets and to the analysis, after liquid-liquid extraction, of urine samples spiked with steroids.

Anabolic Agents↗

PubMed2000

Optimization of the high-performance liquid chromatographic separation of a complex mixture containing urinary steroids, boldenone and bolasterone: application to urine samples.

An HPLC separation of a complex mixture containing 13 urinary anabolics and corticoids, and boldenone and bolasterone (synthetic anabolics) has been carried out. The applied optimization method involved the use of binary, ternary and quaternary mobile phases containing acetonitrile, methanol or tetrahydrofuran as organic modifiers. The effect of different reversed-phase packings and temperature on the separation was studied. The optimum separation was achieved by using a water-acetonitrile (60:40, v/v) mobile phase in reversed-phase HPLC at 30 degrees C, allowing the separation of all the analytes in about 24 min. Calibration graphs were obtained using bolasterone or methyltestosterone as internal standards. Detection limits were in the range 0.012-0.107 microg ml(-1). The optimized separation was applied to the analysis, after liquid-liquid extraction, of human urine samples spiked with steroids.

Adrenal Cortex Hormones↗

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↗

PubMed1999

LC method development for ibuprophen and validation in different pharmaceuticals.

An isocratic LC method for the simultaneous determination of ibuprophen (IBU) and its degradation product (4-isobutylacetophenone) has been developed and validated for different pharmaceuticals (sachets, tablets and gels). The chromatographic separation was achieved with phosphoric acid solution (pH 3.2)-acetonitrile (50:50, v/v) as mobile phase, a Hypersil C18 column and UV detection at 254 nm. In all cases, sample preparation was required before HPLC analysis.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1997

Development and validation of a high-performance liquid chromatography method for the determination of cold relief ingredients in chewing gum.

An isocratic high-performance liquid chromatography (HPLC) method for the simultaneous determination of the active compounds paracetamol, pseudoephedrine and chlorpheniramine in chewing gum samples has been developed and validated. The method required a simple liquid-liquid extraction using n-hexane and a mixture of water-acetonitrile prior to HPLC analysis. The chromatographic separation was achieved with an aqueous solution containing hexylamine (pH 3)-acetonitrile as the mobile phase, a Spherisorb C18 column and UV detection at 220 nm. As an application, the proposed method has been used to evaluate the release into saliva of these compounds from samples under a controlled human chewing process.

Acetaminophen↗

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↗