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Publications (5)7.88 Total impact

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    ABSTRACT: Retention data (retention factor versus acetonitrile content in the mobile phase) on a zwitterionic hydrophilic stationary phase (ZIC-HILIC) of four cationic-type aldoximes (containing one or two pyridinium rings) showed atypical V-shape profiles. Such an unusual behavior is obviously different from reported U-shaped retention plots obtained for non-ionic compounds, where the ionic strength is constant only in an aqueous component. A double retention mechanism may explain such curves: a reversed phase in highly aqueous mobile phases (more than 60%), and a normal phase for mobile phases with a high concentration of acetonitrile (% acetonitrile > 40%). Polynomial and linear equations were used to describe the dependence of the retention factor on the acetonitrile content in the mobile phase. The experimental inflexion point for each analyte is confirmed through calculation of the content of the organic solvent in the mobile phase for which the two retention functions become equal. When ionic strength becomes constant in the mobile phase the reversed phase is dominant and the retention factor versus acetonitrile content in the mobile phase becomes linear over the entire domain.
    Analytical methods 02/2011; 3(2):241-244. · 1.94 Impact Factor
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    ABSTRACT: Direct plasma loading on a LiChrospher ADS C18 cartridge on-line coupled to an analytical Zorbax XDB C18 column was used to analyze felodipine by means of positive atmospheric pressure chemical ionization (APCI) tandem mass spectrometric (MS/MS) detection. Appropriate sensitivity, accuracy, and precision were obtained using an ion trap mass analyzer operated in a multiple reaction monitoring (MRM) mode. Diethyl-4-(2,3-dichlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate) was used as an internal standard. The method was fully validated. The method was successfully applied to a pilot bioequivalence study made on extended release oral dosage forms containing 10 mg of felodipine, under fed and fasting conditions.
    Analytical Letters 05/2010; 43(7):1330-1343. · 0.98 Impact Factor
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    ABSTRACT: 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. 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.
    Journal of pharmaceutical and biomedical analysis 02/2010; 52(4):508-16. · 2.45 Impact Factor
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    ABSTRACT: The sensitivity of the compendial European Pharmacopoeia RPLC/UV method for assaying residual ginkgolic acids in Ginkgo biloba standardized extracts was essentially improved by operating modifications on the sample preparation procedure, including sample injection. The acidified methanol/water solution of the Ginkgo biloba standardized extract was extracted “in situ” with n-hexane (concentration factor of 20). From the organic layer, a relatively large volume (50 µL) of the hexane solution was directly loaded to the chromatographic column. A modified gradient elution profile was used in order to force the sample solvent to elute faster than analytes, without affecting peak symmetry. The separation is obtained in 22 minutes. As the amount of the target compounds loaded to column is higher, selective UV detection at 310 nm was possible. The method was validated according to specific operating guidelines for selectivity, linearity range, quantitation limits, precision, accuracy, and robustness. A limit of quantitation of 1 ppm (five times less than the accepted maximal content threshold for ginkgolic acids in standardized G. biloba extracts) was obtained. Confirmation of the target compounds through MS2 detection and evaluation of the sensitivity afforded by such a detection system are also discussed.
    Journal of Liquid Chromatography &amp Related Technologies 01/2010; 33(1):133-149. · 0.57 Impact Factor
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    ABSTRACT: A sensitive method for determination of free captopril as monobromobimane derivative in plasma samples is discussed. The internal standard (IS) was 5-methoxy-1H-benzimidazole-2-thiol. Derivatization with monobromobimane immediately after blood collection and plasma preparation prevents oxidation of captopril to the corresponding disulfide compound and enhances the ionization yield. Consequently, derivatization enhances sample stability and detection sensitivity. Addition of the internal standard was made immediately after plasma preparation. The internal standard was also derivatized by monobromobimane, as it contains a thiol functional group. Preparation of plasma samples containing captopril and IS derivatives was based upon protein precipitation through addition of acetonitrile, in a volumetric ratio 1:2. The reversed-phase liquid chromatographic separation was achieved on a rapid resolution cartridge Zorbax SB-C(18), monitored through positive electrospray ionization and tandem MS detection using the multiple-reaction monitoring mode. Transitions were 408-362 amu for the captopril derivative and 371-260 amu for the internal standard derivative. The kinetics of captopril oxidation to the corresponding disulfide compound in plasma matrix was also studied using the proposed method. A linear log-log calibration was obtained over the concentration interval 2.5-750 ng/mL. A low limit of quantitation in the 2.5 ng/mL range was obtained. The analytical method was fully validated and successfully applied in a three-way, three-period, single-dose (50 mg), block-randomized bioequivalence study for two pharmaceutical formulations (captopril LPH 25 and 50 mg) against the comparator Capoten 50 mg.
    Biomedical Chromatography 04/2009; 23(10):1092-100. · 1.95 Impact Factor