Victor David

Degradation of pharmaceutical compound pentoxifylline in water by non-thermal plasma treatment.

The decomposition of a model pharmaceutical compound, pentoxifylline, in aqueous solution was investigated using a dielectric barrier discharge (DBD) in coaxial configuration, operated in pulsed regime, at atmospheric pressure and room temperature. The solution was made to flow as a film over the surface of the inner electrode of the plasma reactor, so the discharge was generated at the gas-liquid interface. Oxygen was introduced with a flow rate of 600sccm. After 60min plasma treatment 92.5% removal of pentoxifylline was achieved and the corresponding decomposition yield was 16g/kWh. It was found that pentoxifylline degradation depended on the initial concentration of the compound, being faster for lower concentrations. Faster decomposition of pentoxifylline could be also achieved by increasing the pulse repetition rate, and implicitly the power introduced in the discharge, however, this had little effect on the decomposition yield. The degradation products were investigated by liquid chromatography-mass spectrometry technique (LC-MS). The evolution of the intermediates during plasma treatment showed a fast increase in the first 30min, followed by a slower decrease, so that these products are almost completely removed after 120min treatment time.

Degradation of antibiotics in water by non-thermal plasma treatment

The decomposition of three β-lactam antibiotics (amoxicillin, oxacillin and ampicillin) in aqueous solution was investigated using a dielectric barrier discharge (DBD) in coaxial configuration. Solutions of concentration 100 mg/L were made to flow as a film over the surface of the inner electrode of the plasma reactor, so the discharge was generated at the gas-liquid interface. The electrical discharge was operated in pulsed regime, at room temperature and atmospheric pressure, in oxygen. Amoxicillin was degraded after 10 min plasma treatment, while the other two antibiotics required about 30 min for decomposition. The evolution of the degradation process was continuously followed using liquid chromatography-mass spectrometry (LC-MS), total organic carbon (TOC) and chemical oxygen demand (COD) analyses.

HPLC-DAD determination of Metformin in human plasma using derivatization with p-nitrobenzoyl chloride in a biphasic system

An optimized method for determination of Metformin at ppb level in human plasma is described. Derivatization of Metformin with p-nitrobenzoyl chloride was carried out in a biphasic system. The derivative extracted in the organic layer (dichloromethane) was concentrated and analyzed by HPLC-DAD, using an isocratic elution (water/methanol mixture 65/35), monitored at 280 nm. Good selectivity against co-extracted matrix components was observed. A detection limit of 10 ppb Metformin in human plasma was reached.

Validation of a LC-fluorescence method for determination of free captopril in human plasma, using a pre-column derivatization reaction with monobromobimane

Both derivatization of free captopril in human plasma samples using monobromobimane as fluorescent label and the corresponding HPLC-fluorescence detection (FLD) method were validated. Calibration curve for the fluorescent captopril derivative in plasma samples is linear in the ppb-ppm range with a detection limit of 4 ppb and an identification limit of 10 ppb (P%: 90; nu > or = 5). These methods were successfully applied on bioequivalence studies carried out on some marketed pharmaceutical formulations.

Liquid extraction and HPLC-DAD assay of hydrochlorothiazide from plasma for a bioequivalence study at the lowest therapeutic dose

SummaryThe main parameters considered in optimizing the liquid extraction and quantitative assay were the yield, precision, limit of quantification, time required for extraction and concentration, and quantity of solvent. The influence on these parameters of the following factors was examined: nature of the extracting solvent, quantity of solvent, co-extraction solvent, and duration of stirring. Instead of equilibrium parameters of the involved thermodynamic system, a kinetic approach was preferred in terms of the effective partition ‘constant’, which is not really constant but a function of time and extraction conditions. The final selected method, considered to be rapid and simple, was applied to determine the pharmacokinetics of hydrochlorotiazide (HCT) after administration of Capozide (Bristol-Myers Squibb) tablets containing 50 mg Captopril and 25 mg HCT, to 4 healthy volunteers. The results obtained were in accordance with the pharmacokinetic parameters of HCT reported in the literature.

Retention Phenomena Induced by Large Volume Injection of Solvents Non‐Miscible with the Mobile Phase in Reversed‐Phase Liquid Chromatography

Abstract Enhancement of sensitivity for spectrometric detection in liquid chromatography is obtained when increased sample volumes are loaded into the chromatographic column. A new approach of injecting large volumes of solvents non‐miscible with the mobile phase is proposed. The paper focuses on the retention study of butylated hydroxyanisole (BHA) loaded into the chromatographic column dissolved in liquid alkanes (n‐hexane, n‐heptane, and iso‐octane, respectively) at volumes up to 600 µL. A simple model based on adsorption for explaining the experimental results is proposed. A clear insight of the process was possible by studying the migration of the solvent zone within the column, at different mobile phase compositions and different loaded volumes, by means of refractive index detection. The model allowed calculation of the number of solvent molecules saturating a C8 alkyl chain site within the stationary phase layer. Competition between the analyte and solvent molecules, together with the homogeneity of the “saturation” realized by solvent over the adsorption sites, could explain the experimental results. It was demonstrated that large volume injection of solvents non‐miscible with the mobile phase is possible in RP‐LC with a gradual reduction of retention and a relatively small loss in terms of peak efficiency.

Large volume injection of 1-octanol as sample diluent in reversed phase liquid chromatography: Application in bioanalysis for assaying of indapamide in whole blood

Large volume injection of samples in strong diluents immiscible with the mobile phases used in reversed phase liquid chromatography (RPLC) has been recently introduced in practice. In the present work, the potential of the technique has been evaluated for bioanalytical applications. The process consists of the liquid-liquid extraction of indapamide from whole blood into 1-octanol, followed by the direct injection from the organic layer into the LC. Detection was made through negative electrospray ionization (ESI) and tandem mass spectrometry (MS(2)). The method was developed, validated, and successfully applied to a large number of samples in two bioequivalence studies designed for indapamide 1.5mg sustained release and 2.5mg immediate release pharmaceutical formulations. The performance of the analytical method is discussed based on data resulting from the validation procedure and the completion of the bioequivalence studies.

Hydrophobicity/hydrophilicity descriptors obtained from extrapolated chromatographic retention data as modeling tools for biological distribution: Application to some oxime-type acetylcholinesterase reactivators

Chromatographic retention data obtained from interactions between some oxime-type compounds and different stationary phases (involving hydrophobic interaction, ion pairing formation availability, pi-pi, H-bonding, dipole-dipole, ion-dipole, electrostatic interaction and glycoprotein binding ability) have been studied. The logarithms of the capacity factors extrapolated at 0% or 100% organic solvent, resulting from the functional dependencies between retention and mobile phase composition, were used for estimation of different kind of hydrophobicity or hydrophilicity descriptors (HHDs) of these compounds. The conditions of the chromatographic separation were chosen as close as possible to in-vivo conditions (the aqueous component of the mobile phase has a pH in the physiologic interval 6.8-7.2, 0.9% sodium chloride was added to reproduce ionic strength and isotonic character, and the temperature was set at 37 degrees C). These descriptors characterizing the partition between stationary/mobile phases through specific interactions may be directly used for correlation to biological distribution processes, such as penetration of the blood/brain barrier. Oxime-type compounds used as acetylcholinesterase (AChE, E.C.3.1.1.7) reactivators have been considered for the retention study. The choice is supported by their use in the therapy of acute intoxication with organophosphorus AChE inhibitors (OPIs, especially nerve agents and pesticides), a rather complicated chemistry in solution and a relative lack of data about computational molecular descriptors used for modeling biological partition/distribution. Some correlations between the determined descriptors and computational values have also been discussed.

Retention Behavior of Metformin and Related Impurities in Ion‐Pairing Liquid Chromatography

Abstract The ion‐pair (IP) mechanism was applied to achieve HPLC‐diode‐array detector (DAD) separation and determination of metformin and five related impurities (cyanoguanidine, 1‐methylbiguanidine, melamine, N,N‐dimethylmelamine, and 4,6‐diamino‐1,3,5‐triazin‐2‐yl guanidine). Sodium octanesulphonate (0.010 mol/L) at pH = 3 was used as an ion pair agent in the aqueous component of the mobile phase. Isocratic elution with 80% acetonitrile and 20% aqueous component was applied with a flow rate of 1.2 mL/min. A double end‐capped, 5 µm particle size Inertsil ODS‐2 stationary phase (250 mm length, 4.6 mm internal diameter column) was used. Limit of quantitation (LOQ), as absolute amount of analytes loaded to the column, in the 35–250 pg interval were obtained using detection at 218 nm. Retention data were used in estimating the thermodynamic parameters (enthalpy and entropy) corresponding to the mobile/stationary phase transfer. Correlations between experimental data and data predicted by means of basicity constant, pH, and water/octanol partition coefficient were also achieved.

Analytical issues in HPLC/MS/MS simultaneous assay of furosemide, spironolactone and canrenone in human plasma samples

A new sensitive HPLC/MS/MS method for simultaneous determination of furosemide, spironolactone and canrenone in human plasma samples is presented. Electrospray ionization source (ESI) has been used. The tandem MS detection was performed under MRM conditions, in the negative ion mode for furosemide and indapamide (internal standard 1) and in the positive ion mode for spironolactone, canrenone and nitrazepam (internal standard 2). A simple plasma protein precipitation with acetonitrile was used as sample preparation technique. The chromatographic separation was carried out under the reversed phase mechanism, on a 250 mm length column packed with octadecyl modified silicagel and thermostated at 35 degrees C. The column was operated under isocratic conditions (3:7 aqueous 0.1% formic acid and methanol, v/v) at a flow rate of 0.8 mL/min. Quantitation intervals of 20-1600 ng/mL for furosemide and 2-100 ng/mL for spironolactone and canrenone have been concluded through validation. Precision and accuracy were situated within the accepted thresholds (maximum 15% relative standard deviation and +/-15% percentage bias). The most sensitive aspects relating to the analytical method development and validation were highlighted and critically assessed in order to reach an objective opinion about the real performances and inherent applicability of the method in bioanalysis.