Biomedical subjects

M J Ruiz-Angel

Publications and source records attributed to M J Ruiz-Angel.

10 recordsLinked to original sources

PubMed2005

Ionic liquids versus triethylamine as mobile phase additives in the analysis of beta-blockers.

A comparative study of peak shape, elution behavior, elution strength and resolution of seven beta-blockers (acebutolol, alprenolol, labetalol, metoprolol, nadolol, pindolol and propranolol) chromatographed with aqueous-organic mobile phases containing additives such as the ionic liquid (IL) 1-butyl-3-methylimidazolium (BMIM BF(4)) or triethylamine (TEA) is performed using a conventional reversed-phase Kromasil C(18) column and isocratic elution. The efficiencies and asymmetry factors achieved for the group of beta-blockers in the Kromasil C(18) column improve when the cationic modifiers are added to the aqueous-organic mobile phase as competing additives for the silanol active sites. BMIM BF(4) is a significantly better additive compared to TEA. The improvement is more notably for the asymmetry factor, BMIM BF(4) allowing to obtain higher plate numbers than TEA at the same concentration. The effects of both modifiers on elution strength and retention factors are, however, different. TEA decreases the solute retention factors when BMIM BF(4) does not change them significantly. Using other additives taken in the IL family such as 1-butyl-3-methylimidazolium hexafluorophosphate and 1-octyl-3-methylimidazolium tetrafluoroborate (OMIM BF(4)), it is shown that the silanol screening effect is always observed, due to the IL cation, when it is possible to increase or to decrease the solute retention factors playing with the hydrophobic nature or chaotropic character of its anion.

Adrenergic beta-Antagonists↗

PubMed2005

Alkane effect in the Arizona liquid systems used in countercurrent chromatography.

Countercurrent chromatography (CCC) is a separation technique that uses a biphasic liquid system; one liquid phase is the mobile phase, the other liquid phase is the stationary phase. Selection of the appropriate liquid system can be a problem in CCC, since it is necessary to select both the "column" and the mobile phase at the same time as the first is completely dependent on the second. A range of systems with various proportions of solvents were developed to ease this choice; 23 variations of the heptane/ethyl acetate/methanol/water biphasic liquid system were labeled A to Z. This range proved to be extremely useful and became the popular Arizona (AZ) liquid system. However, authors often replace the heptane with hexane. In this work, the chemical compositions of the upper phases and the lower phases of 55 Arizona systems made with various alkanes (pentane, hexane, heptane, isooctane and cyclohexane) were determined by gas chromatography and Karl Fischer titration. The test mixture separated consisted of five steroid compounds. The lower phases were found to have similar compositions when different alkanes were used, but the upper phases were found to change. Exchanging heptane for hexane or isooctane produced minimal changes in the CCC chromatogram, while changing the proportions of the solvents resulted in an exponential change in the retention volumes. The high density of cyclohexane made liquid stationary phase retention difficult. All Arizona systems equilibrated within 30 min, but were not stable: water slowly hydrolyzed the ethyl acetate (as shown by a continuous decrease in the pH of the lower aqueous phase), especially in the water-rich systems (early alphabet letters).

Acetates↗

PubMed2005

Effect of ionization and the nature of the mobile phase in quantitative structure-retention relationship studies.

The octanol-water distribution constant, commonly called partition coefficient, Po/w, is a parameter often retained as a measure of the hydrophobicity of a molecule. log Po/w, for a given molecule, can be conveniently evaluated constructing correlation lines between standard retention factor logarithms (log k) in reversed-phase liquid chromatography (RPLC) and standard log Po/w values. Many compounds of pharmaceutical interest can be quite hydrophobic and have, simultaneously, basic nitrogen atoms or acidic sulfur containing groups in their structure. This renders them ionizable. The hydrophobicity of the molecular drug form (Po/w value) is completely different from its ionic form (log Po/w(+ or -) value). The actual hydrophobicity of such ionizable molecule depends on the pH. It can be represented by an apparent Papp value that takes into account the amount of compound in its molecular and ionic state combining the Po/w and Po/w(+ or -) values. In this work, log k in RPLC for ionizable as well as non-ionizable pharmaceutical compounds with different therapeutic properties (10 beta-blockers, seven tricyclic antidepressants (TA), eight steroids and 12 sulfonamides) were correlated with log Po/w. Similar correlations were done between log k and the corrected log Papp values at pH 3. Aqueous-organic mobile phases containing acetonitrile (conventional RPLC) and micellar-organic mobile phases (micellar liquid chromatography, MLC), prepared with the anionic surfactant sodium dodecyl sulfate and the organic solvents acetonitrile, propanol or pentanol, were also used to elute the compounds. All mobile phases were buffered at pH 3. Using conventional retention RPLC data, the correlation of log k with log Po/w, was satisfactory for steroids because they cannot ionize. For ionizable beta-blockers and TAs, the use of log Papp values improved the quality of the correlations, but yielded similar results for sulfonamides. In MLC, since an electrostatic interaction is added to hydrophobic forces, poorer correlations were obtained in all cases. The retention data obtained in RPLC also seems to correlate better with the biological activity of the drugs.

Chromatography, Liquid↗

PubMed2004

Micellar versus hydro-organic mobile phases for retention-hydrophobicity relationship studies with ionizable diuretics and an anionic surfactant.

Logarithm of retention factors (log k) of a group of 14 ionizable diuretics were correlated with the molecular (log P o/w) and apparent (log P(app)) octanol-water partition coefficients. The compounds were chromatographed using aqueous-organic (reversed-phase liquid chromatography, RPLC) and micellar-organic mobile phases (micellar liquid chromatography, MLC) with the anionic surfactant sodium dodecyl sulfate (SDS), in the pH range 3-7, and a conventional octadecylsilane column. Acetonitrile was used as the organic modifier in both modes. The quality of the correlations obtained for log P(app) at varying ionization degree confirms that this correction is required in the aqueous-organic mixtures. The correlation is less improved with SDS micellar media because the acid-base equilibriums are shifted towards higher pH values for acidic compounds. In micellar chromatography, an electrostatic interaction with charged solutes is added to hydrophobic forces; consequently, different correlations should be established for neutral and acidic compounds, and for basic compounds. Correlations between log k and the isocratic descriptors log k(w), log k(wm) (extrapolated retention to pure water in the aqueous-organic and micellar-organic systems, respectively), and psi0 (extrapolated mobile phase composition giving a k = 1 retention factor or twice the dead time), and between these descriptors and log P(app) were also satisfactory, although poorer than those between log k and log P(app) due to the extrapolation. The study shows that, in the particular case of the ionizable diuretics studied, classical RPLC gives better results than MLC with SDS in the retention hydrophobicity correlations.

Chromatography, High Pressure Liquid↗

PubMed2004

Effects of pH and the presence of micelles on the resolution of diuretics by reversed-phase liquid chromatography.

A comparative study on the performance of two RPLC modes on the separation of 18 diuretics with diverse acid-base behaviour (acetazolamide, althiazide, amiloride, bendroflumethiazide, benzthiazide, bumetanide, canrenoic acid, chlorothiazide, chlorthalidone, ethacrynic acid, furosemide, hydrochlorothiazide, piretanide, probenecid, spironolactone, triamterene, trichloromethiazide and xipamide) was carried out. A conventional octadecylsilane column and acidic acetonitrile-water mobile phases, in the absence and presence of micelles of the anionic surfactant sodium dodecyl sulphate (SDS), were used. The effects of pH and the modifiers acetonitrile and SDS on peak asymmetry, efficiency, selectivity, resolution and analysis time, were examined. The comparison of both RPLC modes (aqueous- and micellar-organics) was done using the same processing tools, applying several polynomial and mechanistic equations to describe the retention. The best separations were obtained by maximising the product of peak purities, considering a wide range of experimental conditions. The study illustrates that, despite the theoretical and practical complexity of the problem, the predicted optimal chromatograms can be reproduced experimentally with great accuracy. None of the examined RPLC modes was able to yield baseline separation of the 18 diuretics. However, their selectivity was complementary, being appropriate for different combinations of a smaller number of the assayed diuretics.

Chromatography, Liquid↗

PubMed2003

Optimised procedures for the reversed-phase liquid chromatographic analysis of formulations containing tricyclic antidepressants.

The chromatographic behaviour (retention, selectivity, peak shape and resolution) of seven tricyclic antidepressants (TCAs), amitryptiline, clomipramine, doxepin, imipramine, maprotiline, nortryptiline and trimipramine, was examined. Conventional unendcapped Cs and C18 columns and an endcapped XTerra MS C18 column recommended for the analysis of basic compounds were used together with acetonitrile-water and micellar sodium dodecylsulfate (SDS)-pentanol mobile phases. The two best combinations were XTerra C18/acetonitrile, which yielded the largest efficiencies and resolution, and C8/SDS-pentanol, which eliminated the peak tails that were still observed with the XTerra C18 column. Both the systems were used to develop simple chromatographic procedures for the control of TCAs in pharmaceutical formulations using UV detection. The selected mobile phase compositions were 35% (v/v) acetonitrile (XTerra C18 column) and 0.075 M SDS-6% (v/v) pentanol (C8 column), both at pH 3. Satisfactory recoveries were achieved in both cases, with intra- and inter-day relative standard deviations (RSDs) always below 0.6 and 2.0%, respectively. The preparation of the samples was simple in both modes, since a previous extraction of the drugs was not needed. The micellar mode has, however, the advantage of using a smaller amount of organic solvent, which is retained in the micellar SDS solution. The C8 column is also less expensive.

Acetonitriles↗

PubMed2003

Improvement of peak shape and separation performance of beta-blockers in conventional reversed-phase columns using solvent modifiers.

A comparative study of peak shape, elution behavior, and resolution of 16 beta-blockers (acebutolol, alprenolol, atenolol, bisoprolol, carteolol, celiprolol, esmolol, labetalol, metoprolol, nadolol, oxprenolol, pindolol, practolol, propranolol, sotalol, and timolol) chromatographed with hybrid mobile phases of triethylamine (TEA)-acetonitrile and sodium dodecyl sulfate (SDS)-propanol is performed using conventional reversed-phase columns and isocratic elution. Both solvent modifiers (TEA and SDS) prevent the interaction of the basic drugs with the alkyl-bonded phase. However, the protection mechanisms of silanols on the packing are different. Whereas TEA associates with the silanol sites (blocking ion-exchange processes or repelling the solutes), the long hydrophobic chain of SDS is inserted in the bonded organic layer with the sulfate group protruding outside, which makes the stationary phase negatively charged. The effects of TEA, acetonitrile, SDS, and propanol on the elution strength, efficiency, peak asymmetry, and resolution are examined under an experimental design basis that is assisted by computer simulation to reach more general conclusions. The combination of improved peak shapes, larger selectivity, and a smaller range in retention among compounds of extreme polarity leads to the observation that a greater number of beta-blockers can be resolved with a hybrid micellar system.

Adrenergic beta-Antagonists↗

PubMed2002

Micellar liquid chromatography: suitable technique for screening analysis.

The screening capability of micellar liquid chromatography (MLC) is discussed using the reported chromatographic data of several sets of compounds (amino acids, beta-blockers, diuretics, phenethylamines, phenols, polynuclear aromatic hydrocarbons, steroids and sulfonamides) and new results (sulfonamides and steroids). The chromatographic data are treated with an interpretive optimisation resolution procedure to obtain the best separation conditions. Usually, the pH and the concentration of surfactant (sodium dodecyl sulfate, SDS, or cetyltrimethylammonium bromide) for the optimal mobile phase were 2.5-3 and < 0.12 M, respectively. The nature and concentration of organic solvent depended on the polarity of the eluted compounds: a low volume fraction of propanol (approximately 1%, v/v) was useful to separate the amino acids, with log P(o/w) < -1 (where P(o/w) is the octanol-water partition coefficient). A greater concentration of this solvent (approximately 5-7%) was needed for compounds in the range -1 < log P(o/w) < 2, as with the studied diuretics and sulfonamides, and a high concentration of propanol (approximately 15%) or a low concentration of butanol (< 10%) had to be used for less polar compounds with 1 < log P(o/w) < 3, such as the beta-blockers. Pentanol (< 6%) was more suitable for the even less polar compounds with log P(o/w) > 3, such as the steroids. For basic drugs such as the phenethylamines (0 < log P(o/w) < 1.7), eluted with a micellar eluent of anionic SDS, propanol was too weak. A study is also shown for mixtures of sulfonamides (log P(o/w) = -1.2 to 1.7) and steroids (log P(o/w) = 3.0-8.1) eluted from conventional C18 columns with SDS mobile phases containing acetonitrile and 1-pentanol, respectively, which are compared with classical acetonitrile-water and methanol-water mixtures. The results complement a previous study on beta-blockers (log P(o/w) = -0.03 to 2.8) and reveal that MLC is a very competitive technique for the screening of compounds against conventional RPLC, due to its peculiar behaviour with regard to the selectivity and elution strength. The concentration of organic solvent needed to obtain sufficiently low retention times (even for highly hydrophobic steroids with log P(o/w) = 7-8) is also appreciably smaller for MLC, which reduces the environmental impact of the mobile phases.

Chromatography, Liquid↗

PubMed2002

Control of propranolol intake by direct chromatographic detection of alpha-naphthoxylactic acid in urine.

A rapid chromatographic procedure with a C18 column, a mobile phase of 0.15 M sodium dodecyl sulfate (SDS)-10% (v/v) 1-propanol at pH 3 (0.01 M phosphate buffer), and fluorimetric detection, is reported for the control of propranolol (PPL) intake in urine samples, which are injected directly without any other treatment than filtration. The peak of PPL was only observed in samples taken a few hours after ingestion of the drug due to its extensive conjugation and metabolisation. The detection of several unconjugated PPL metabolites was therefore considered: desisopropylpropranolol (DIP), propranolol glycol (PPG), alpha-naphthoxylactic acid (NLT) and alpha-naphthoxyacetic acid (NAC). NLT showed the best characteristics: it eluted at a much shorter retention time than PPL, its concentration in urine samples was greater and it did not present any interference from endogeneous compounds in urine, common drugs or drugs administered in combination with PPL. The limit of quantification, measured as the concentration of analyte providing a relative standard deviation of 20%, was 24 ng/ml, and the day-to-day imprecision was below 4% for concentrations above 200 ng/ml. The procedure allows the routine control of PPL at therapeutic urine levels. Urinary excretion studies showed that the detection of NLT is possible at least up to 20-30 h after oral administration.

Adrenergic beta-Antagonists↗

PubMed2002

Determination of furosemide in urine samples by direct injection in a micellar liquid chromatographic system.

A sensitive, selective and efficient micellar liquid chromatographic (MLC) procedure was developed for the determination of furosemide (4-chloro-N-furfuryl-5-sulfamoylanthranilic acid) in urine samples by direct injection and UV detection. The procedure makes use of a C18 reversed-phase column and a micellar mobile phase of 0.05 mol l(-1) sodium dodecyl sulfate-6% v/v propanol and phosphate buffer at pH 3 to resolve furosemide from its photochemical degradation products. The importance of protecting the standards and urine samples to be analysed from light in the assay of furosemide, avoiding its degradation, was verified. The limit of quantification was 0.15 microg ml(-1) and the relative standard deviation of the inter-day assay was 0.8-0.04% in the 6-82 microg ml(-1) range. Detection of urinary excretion of furosemide was followed up to 12 h after ingestion of the drug by a healthy volunteer. No potential interference from the major metabolite (furosemide acylglucuronide) and its hydrolytic product (4-chloro-5-sulfamoylanthranilic acid) was observed. Commonly administered drugs also did not interfere. The proposed MLC procedure permits the rapid and reproducible measurement of low levels of furosemide in a small amount of urine.

Chromatography, High Pressure Liquid↗