M.G. Quaglia

Simultaneous determination of losartan and hydrochlorothiazide in tablets by high-performance liquid chromatography.

A method for the simultaneous determination of losartan potassium and hydrochlorothiazide in tablets is described. The procedure, based on the use of reversed-phase high-performance liquid chromatography, is linear in the concentration range 3.0-7.0 microg ml(-1) for losartan and 0.5-2.0 microg ml(-1) for hydrochlorothiazide, is simple and rapid and allows accurate and precise results. The limit of detection was 0.08 microg ml(-1) for losartan and 0.05 microg ml(-1) for hydrochlorothiazide.

Determination of silymarine in the extract from the dried silybum marianum fruits by high performance liquid chromatography and capillary electrophoresis

Silybine (SBN), isosilybine (ISBN), silycristine (SCN), silydianine (SDN), and taxifoline (TXF) are the main active flavanoids, generally found in the dried fruits of silybum marianum. The concentrations of these compounds, excepted TXF, are all together usually expressed as silymarine content. In this paper the determination of the silymarine titre was made by high performance liquid chromatography (HPLC), and high performance capillary electrophoresis (HPCE). Two reversed stationary phases, RP-18 and RP-8, were observed comparing the resolutions of all considered flavanoids with each stationary phases. The HPCE was carried out considering the possible improvement in the resolution of SBN, CN, SDN and TXF using, 8-cyclodextrines or organic modifier. The qualitative and quantitative data obtained by HPLC and HPCE were compared.

Determination of losartan and hydrochlorothiazide in tablets by CE and CEC.

Capillary Electrophoresis (CE) and Capillary Electrochromatography (CEC) have been used to determine losartan and hydrochlorothiazide. The CE separation was carried out in an uncoated capillary filled with a 100 mM sodium borate pH 9 solution containing trimethyl-beta-cyclodextrins. CEC was performed using a capillary packed with a RP-18 stationary phase. The mobile phase was a mixture of 50 mM ammonium acetate pH 7, water, acetonitrile (1/1.5/7.5). By CE and CEC suitable methods to determine simultaneously losartan and hydrochlorothiazide in working standard mixture or pharmaceutical form were obtained. The proposed methods are very simple and both gave accurate and precise results.

Use of vancomycin silica stationary phase in packed capillary electrochromatography: III. Enantiomeric separation of basic compounds with the polar organic mobile phase

The separation of basic compounds into their enantiomers was achieved using capillary electrochromatography in 50 or 75 νm inner diameter (ID) fused‐silica capillaries packed with silica a stationary phase derivatized with vancomycin and mobile phases composed of mixtures of polar organic solvents containing 13 mM ammonium acetate. Enantiomer resolution, electroosmotic flow, and the number of theoretical plates were strongly influenced by the type and concentration of the organic solvent. Mobile phases composed of 13 mM ammonium acetate dissolved in mixtures of acetonitrile/methanol, ethanol, n‐propanol, or isopropanol were tested and the highest enantioresolutions were achieved using the first mobile phase, allowing the separation of almost all investigated enantiomers (9 from 11 basic compounds). The use of capillaries with different ID (50 and 75 νm ID) packed with the same chiral stationary phase revealed that a higher number of theoretical plates and higher enantioresolution was achieved with the tube with lowest ID.*

Separation of tocopherols by nano-liquid chromatography

Nanoliquid chromatography (nano-LC) was used for the separation of tocopherols (delta-, gamma-, alpha-TOH), alpha-tocopherol acetate (alpha-TOH-Ac) and an antioxidant compound, namely butylated hydroxytoluene (BHT) used to prevent TOHs autoxidation. The separation was carried out in a fused silica capillary of 100 microm I.D. and 375 microm O.D. packed in our laboratory with RP18 silica stationary phase of either 5- or 3-microm diameter (23-cm long). The mobile phase was composed by mixtures of methanol (MeOH), acetonitrile (MeCN) and water. Typical analyses time for the separation of all the five components of the mixture were 6-9 min depending on the composition of the mobile phase. Efficiency and resolution were strongly influenced by the particle diameter and the highest Rs and N/m values were observed using 3-microm RP18 particles. Experiments performed with capillaries packed with 3-microm RP18 particles provided good limit of detection (LOD) and limit of quantification (LOQ) (for delta-, gamma-TOH, alpha-TOH-Ac were 4 and 8 microg/ml, while for alpha-TOH were 6 and 10 microg/ml, respectively). The optimized method was applied to extracts of serum and pharmaceutical preparation containing alpha-TOH and alpha-TOH-Ac.

Enantioseparation and anti-rhinovirus activity of 3-benzylchroman-4-ones

In a series of homo-isoflavonoids, chloro-substituted rac-3-benzylchroman-4-ones (3 d-f) showed an antiviral in vitro activity against selected picornaviruses. In order to study the anti-rhinovirus activity of each stereoisomer, racemic mixtures of 3 d and 3 e were successfully resolved by high-performance liquid chromatography, using a Whelk-O 1 column as chiral stationary phase. The CD spectra confirm that the two eluates of each compound are enantiomers but do not allow the assignment of their absolute configurations. The antiviral activity of the isomers and their racemates was tested in vitro against human rhinovirus serotype 1B and 14 infection, by means of the plaque reduction assay. All homoisoflavonoids tested exhibited an inhibitory effect on rhinovirus replication with an activity depending on virus serotype and compound. The two enantiomers of each compound and the corresponding racemate were equipotent, clearly showing that the configuration of the chiral center in position 3 does not influence the activity against both rhinovirus serotypes.

Separation of δ-, γ- and α-tocopherols by CEC

Abstract In this study capillary electrochromatography (CEC) was used for the separation of three tocopherols (TOHs), namely δ-, γ- and α-TOH and the antioxidant compound, butylated hydroxytoluene (BHT). The CEC experiments were carried out using an octadecylsilica (ODS) stationary phase packed, in our laboratory, in a fused-silica capillary (100 μm I.D., 365 μm O.D.×33 cm of total length and 24.6 or 8.4 cm effective length). The mobile phase was composed by a mixture of methanol (MeOH) and acetonitrile (ACN), at different concentrations and 0.01% (w/v) of ammonium acetate. Retention time ( t R ), retention factor ( k ), resolution ( R s ) of the three TOHs were strongly influenced by the organic solvent composition of the run buffer and by the effective length of the capillary. Optimum experimental conditions were found even employing the short effective length of the capillary achieving the baseline separation of the studied analytes in a relatively short time (less than 5 min). The optimized method was applied to the qualitative analysis of vitamin E (α-TOH) present in a human serum extract.

Use of short-end injection capillary packed with a glycopeptide antibiotic stationary phase in electrochromatography and capillary liquid chromatography for the enantiomeric separation of hydroxy acids

A new chiral stationary phase (CSP) was prepared by reacting MDL 63,246 (Hepta-Tyr), a glycopeptide antibiotic belonging to the teicoplanin family, with 5-microm diol-silica particles. The CSP mixed with 5-microm amino silica particles (3:1) was packed into 75-microm fused-silica capillaries for only 6.6 cm and used for electrochromatographic experiments analyzing several hydroxy acid enantiomers. A reversed electroosmotic flow carried both analytes and mobile phase towards the anode in a short time (1-3 min), being baseline resolved all the studied analytes. In order to achieve the fastest enantiomeric resolution of the studied hydroxy acids, the effect of several experimental parameters such as mobile phase composition (organic modifier type and concentration, pH of the buffer and ionic strength), capillary temperature and applied voltage on enantioresolution factor, retention time, enantioselectivity were evaluated. The packed capillary column allowed the separation of mandelic acid enantiomers in less than 72 s with resolution factor Rs=2.18 applying a voltage of 30 kV and eluting with a mobile phase composed by 50 mM ammonium acetate (pH 6)-water-acetonitrile (1:4:5, v/v). The CSP was also tested in the capillary liquid chromatography mode resolving all the studied enantiomers applying 12 bar pressure to the mobile phase [50 mM ammonium acetate (pH 6)-water-methanol-acetonitrile, 1:4:2:3, v/v)], however, relatively long analysis times were observed (12-20 min).

Chiral resolution and molecular modeling investigation of rac-2-cyclopentylthio-6-[1-(2,6-difluorophenyl)ethyl]-3,4-dihydro-5- methylpyrimidin-4(3H)-one (MC-1047), a potent anti-HIV-1 reverse transcriptase agent of the DABO class.

rac-2-Cyclopentylthio-6-[1-(2,6-difluorophenyl)ethyl]-3,4-dihydro-5-methylpyrimidin-4(3H)-one (MC-1047) is a potent inhibitor of HIV-1 multiplication in acutely infected cells. MC-1047 racemate has been resolved by chiral HPLC using, as chiral stationary phase (CSP), a commercially available (R,R)-Whelk-01 column. The optical purity and the circular dichroism (CD) of the two resolved enantiomers were determined and their biological activities tested in in vitro assays. Molecular modeling inspection of the binding of (R) and (S) enantiomers to the non-nucleoside binding site (NNBS) of reverse transcriptase (RT) using the defined model of F(2)-S-DABO/RT complex indicates the (R) enantiomer as the more active isomer.

Determination of the binding of a β2-blocker drug, frusemide and ceftriaxone to serum proteins by capillary zone electrophoresis

Abstract A modified Hummel-Dreyer method was used to study the binding of drugs with serum proteins by high performance capillary electrophoresis. The study was carried out to check the possible interaction between serum proteins and a highly selective β 2 -blocker, ICI 118551 (ICI). To prove the suitability of the method the protein binding of frusemide and ceftriaxone, drugs previously investigated, was also studied. The analyses were carried out by injecting a solution of sα 1 -acidic glycoprotein ( α 1 -AGP) or human serum albumin in 70 mM NaH 2 PO 4 : Na 2 HPO 4 (pH 7.4) buffer into an uncoated fused silica capillary filled with the same buffer. In the capillary, maintained at a working temperature of 35°C, a known amount of the ICI, frusemide or ceftriaxone was added. The method allows the bound drug to be determined directly.