Javier Gotta

National University of La Plata, La Plata, Provincia de Buenos Aires, Argentina

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Publications (4)11.23 Total impact

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    ABSTRACT: The prediction capability of the solvation parameter model in reverse-phase liquid chromatography at different methanol-water mobile phase compositions and temperatures was investigated. By using a carefully selected set of solutes, the training set, linear relationships were established through regression equations between the logarithm of the solute retention factor, logk, and different solute parameters. The coefficients obtained in the regressions were used to create a general retention model able to predict retention in an octadecylsilica stationary phase at any temperature and methanol-water composition. The validity of the model was evaluated by using a different set (the test set) of 30 solutes of very diverse chemical nature. Predictions of logk values were obtained at two different combinations of temperature and mobile phase composition by using two different procedures: (i) by calculating the coefficients through a mathematical linear relationship in which the mobile phase composition and temperature are involved; (ii) by using a general equation, obtained by considering the previous results, in which only the experimental values of temperature and mobile phase composition are required. Predicted logk values were critically compared with the experimental values. Excellent results were obtained considering the diversity of the test set.
    Journal of Separation Science 09/2012; 35(20):2699-709. · 2.59 Impact Factor
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    ABSTRACT: The natural alkaloid quinine (QN) was immobilized on porous silica particles, and part of the material was subsequently endcapped with n-hexyl hydrocarbon chains. Two synthetic strategies for silanization of the support were first compared. These columns were thoroughly evaluated in order to study the influence of endcapping in the enantiorecognition features. Enantioseparations of twenty N-derivatized 2,4-dinitrophenyl α-amino acids (DNP-amino acids) were studied by changing mobile phase pH, buffer concentration, type of organic solvent in the mobile phase, and column temperature. Maximum retention factors were observed at pH ≈6, at this intermediate pH the tertiary amine of the quinine is protonated to a high degree and therefore available for strong electrostatic interactions with unprotonated anionic DNP-amino acids. The enantioselectivity factors, however, increased as the pH did in the range between 5 and 7. The increase in ionic strength had influence on retention, but not on enantioselectivity, allowing the use of this variable for optimization of retention factors. Finally, the thermodynamic transfer parameters of the enantiomers from the mobile to both CSPs (with and without endcapping, QN-CSP(EC) and QN-CSP, respectively) were estimated from van't Hoff plots within the range of 10-40 °C. Thus, the differences in the transfer enthalpy, Δ(ΔH°), and transfer entropy, Δ(ΔS°), enabled an investigation of the origin of the differences in interaction energies.
    Journal of chromatography. A 06/2011; 1218(23):3660-8. · 4.19 Impact Factor
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    ABSTRACT: We developed an improved reversed-phase high-performance liquid chromatography (RPLC) assay for the rapid separation and determination of the 2-hydroxyethidium ion. The 2-hydroxyethidium ion is the specific product of the redox reaction between hydroethidine with superoxide radical. High resolution between the chromatographic bands corresponding to ethidium and 2-hydroxyethidium ions was achieved within a practicable analysis time. The RPLC-fluorescence method can reliably detect 2-hydroxyethidium ion concentrations down to 0.12 [small micro]M (or 1.2 pmol) and the signal is linear with concentration beyond 50 [small micro]M. An application of the method to neutrophil samples demonstrated that intracellular quantification of 2-hydroxyethidium was reproducible, as evidenced by low values of the relative standard deviations: 0.016 for non-stimulated cells, and 0.056 and 0.0125 for neutrophils incubated with agonists phorbol myristate acetate (PMA) and N-formyl-methionyl-leucyl-phenylalanine (fMLP), respe
    Analytical methods 01/2011; 3(3):593-598. · 1.86 Impact Factor
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    ABSTRACT: Recent developments in HPLC methods have focused on various strategies in order to increase the speed of analysis. One area of impressive growing is column technology. Today, analytical methods that propose the use of short columns packed with sub-2 μm particles installed in ultra high-pressure LC instruments are not uncommon. Another strategy consisted of heating thermally resistant columns to temperatures well above of 100°C in order to reduce eluent viscosities and, therefore, column backpressure. We discuss experimental conditions for achieving high-throughput analysis using standard instruments with a few simple modifications. The chromatographic performance of two particulated and a silica-based monolithic column operated at moderate temperatures and flow rates are compared. The monolithic column proved to be stable over several thousands column volumes at 60°C. More important, its resistance to mass transfer at this temperature was significantly reduced. Very fast separations of two different mixtures of pharmaceutical compounds, anti-inflammatory drugs and β-blockers, were achieved with the three columns at 60°C by using ACN/buffer at 5 mL/min. Excellent peak shapes of basic solutes and quite reasonable resolutions were achieved in very short analysis times with columns operated at temperatures moderately higher than the usual room temperature.
    Journal of Separation Science 09/2010; 33(17-18):2645-53. · 2.59 Impact Factor