The Experts below are selected from a list of 33444 Experts worldwide ranked by ideXlab platform

P. Daniel Dapkus - One of the best experts on this subject based on the ideXlab platform.

Adam Mock - One of the best experts on this subject based on the ideXlab platform.

Georges Guiochon - One of the best experts on this subject based on the ideXlab platform.

  • peak Compression Factor of proteins
    Journal of Chromatography A, 2009
    Co-Authors: Fabrice Gritti, Georges Guiochon
    Abstract:

    An experimental protocol is proposed in order to measure with accuracy and precision the band Compression Factor G(12)(2) of a protein in gradient RPLC. Extra-column contributions to bandwidth and the dependency of both the retention Factor and the reduced height equivalent to a theoretical plate (HETP) on the mobile phase composition were taken into account. The band Compression Factor of a small protein (insulin, MW kDa) was measured on a 2.1mm x 50mm column packed with 1.7 microm C(4)-bonded bridged ethylsiloxane BEH-silica particles, for 1 microL samples of dilute insulin solution (<0.05g/L). A linear gradient profile of acetonitrile (25-28% acetonitrile in water containing 0.1% trifluoroacetic acid) was applied during three different gradient times (5, 12.5, and 20 min). The mobile phase flow rate was set at 0.20 mL/min in order to avoid heat friction effects (maximum column inlet pressure 180 bar). The band Compression Factor of insulin is defined as the ratio of the experimental space band variance measured under gradient conditions to the reference space band variance, which would be observed if no thermodynamic Compression would take place during gradient elution. It was 0.56, 0.71, and 0.76 with gradient times of 5, 12.5, and 20 min, respectively. These Factors are 20-30% smaller than the theoretical band Compression Factors (0.79, 0.89, and 0.93) calculated from an equation derived from the well-known Poppe equation, later extended to any retention models and columns whose HETP depends on the mobile phase composition. This difference is explained in part by the omission in the model of the effect of the pressure gradient on the local retention Factor of insulin during gradient elution. A much better agreement is obtained for insulin when this effect is taken into account. For lower molecular weight compounds, the pressure gradient has little effect but the finite retention of acetonitrile causes a distortion of the gradient shape during the migration of its breakthrough front along the column. This phenomenon should be taken into account in the theoretical models.

  • Peak Compression Factor of proteins.
    Journal of chromatography. A, 2009
    Co-Authors: Fabrice Gritti, Georges Guiochon
    Abstract:

    An experimental protocol is proposed in order to measure with accuracy and precision the band Compression Factor G(12)(2) of a protein in gradient RPLC. Extra-column contributions to bandwidth and the dependency of both the retention Factor and the reduced height equivalent to a theoretical plate (HETP) on the mobile phase composition were taken into account. The band Compression Factor of a small protein (insulin, MW kDa) was measured on a 2.1mm x 50mm column packed with 1.7 microm C(4)-bonded bridged ethylsiloxane BEH-silica particles, for 1 microL samples of dilute insulin solution (

  • experimental band Compression Factor of a neutral compound under high pressure gradient elution
    Journal of Chromatography A, 2008
    Co-Authors: Fabrice Gritti, Georges Guiochon
    Abstract:

    Abstract To measure the gradient Compression Factor for a low molecular weight compound (caffeine, MW = 194  g/L), 1  μ L samples of solution were injected into a 2.1 mm × 100  mm column packed with bridged ethylsiloxane BEH-silica. These samples were successively run under isocratic and gradient elution modes. Both chromatograms were recorded with either a low ( 250  bar) or a high pressure drop ( > 650  bar), corresponding to flow rates of 0.10 and 0.35 mL/min, respectively. Caffeine was eluted with a mixture of methanol and water at room temperature. The efficiency and the retention Factors of caffeine on the BEH-C18column were measured as a function of the mobile phase composition under isocratic conditions. During the gradient elution, the methanol concentration was increased from 10 to 25% (v/v). The experimental Compression Factors measured are in excellent agreement with those predicted with an equation previously derived, which is valid at low flow rates and for smooth gradients. The negative relative difference observed between experimental and theoretical values at high flow rates originates from the compressibility of the eluent. Using a high gradient steepness to perform fast gradient elution limits the degree of band Compression that can be achieved, even when the radial temperature gradient across the column is as small as 0.2 K.

  • Experimental band Compression Factor of a neutral compound under high pressure gradient elution.
    Journal of chromatography. A, 2008
    Co-Authors: Fabrice Gritti, Georges Guiochon
    Abstract:

    To measure the gradient Compression Factor for a low molecular weight compound (caffeine, MW=194 g/L), 1 microL samples of solution were injected into a 2.1 mm x 100 mm column packed with bridged ethylsiloxane BEH-silica. These samples were successively run under isocratic and gradient elution modes. Both chromatograms were recorded with either a low (650 bar), corresponding to flow rates of 0.10 and 0.35 mL/min, respectively. Caffeine was eluted with a mixture of methanol and water at room temperature. The efficiency and the retention Factors of caffeine on the BEH-C(18)column were measured as a function of the mobile phase composition under isocratic conditions. During the gradient elution, the methanol concentration was increased from 10 to 25% (v/v). The experimental Compression Factors measured are in excellent agreement with those predicted with an equation previously derived, which is valid at low flow rates and for smooth gradients. The negative relative difference observed between experimental and theoretical values at high flow rates originates from the compressibility of the eluent. Using a high gradient steepness to perform fast gradient elution limits the degree of band Compression that can be achieved, even when the radial temperature gradient across the column is as small as 0.2K.

  • Exact peak Compression Factor in linear gradient elution. I. Theory.
    Journal of chromatography. A, 2008
    Co-Authors: Fabrice Gritti, Georges Guiochon
    Abstract:

    The only existing expression for the peak Compression Factor in linear gradient elution chromatography assumes that the linear-solvent-strength model (LSSM) applies to the retention of the compound studied, that the column efficiency is independent of the mobile phase composition, and that, during gradient elution, the relative retention Factor of a compound inside its band varies linearly with the distance from the band center. Because the retention Factors of many analytes in reversed-phase liquid chromatography do not rigorously follow the LSSM, we extend the theoretical approach of Poppe et al. to the prediction of peak Compression Factors in linear gradient elution chromatography for any retention model, when column efficiency varies with the mobile phase composition. Only the contribution of the chromatographic column to the peak Compression was taken into account, the contribution of the dwell volume being neglected. A second restriction is the linearity of the relative retention Factor as a function of the position along the band width inside the column. These constraints could be the sources for the difference observed between experimental and theoretical values of peak Compression Factors. When the retention Factor varies steeply with the mobile phase composition, such as with proteins or large peptides in RP-HPLC, it is found that the thermodynamic Compression term, which tends to sharpen the peak, is coupled with the column dispersion term, which tends to broaden the peak. This coupling term acts as an apparent dispersion term, contributing to broaden the peak. This result is consistent with the measurements of peak Compression Factors found in the literature.

Dakshayani S Jangamashetti - One of the best experts on this subject based on the ideXlab platform.

  • multi band frequency Compression for improving speech perception by listeners with moderate sensorineural hearing loss
    Speech Communication, 2012
    Co-Authors: Pandurangarao N Kulkarni, Prem C Pandey, Dakshayani S Jangamashetti
    Abstract:

    In multi-band frequency Compression, the speech spectrum is divided into a number of analysis bands, and the spectral samples in each band are compressed towards the band center by a constant Compression Factor, resulting in presentation of the speech energy in relatively narrow bands, for reducing the effect of increased intraspeech spectral masking associated with sensorineural hearing loss. Earlier investigation assessing the quality of the processed speech showed best results for auditory critical bandwidth based Compression using spectral segment mapping and pitch-synchronous analysis-synthesis. The objective of the present investigation is to evaluate the effectiveness of the technique in improving speech perception by listeners with moderate to severe sensorineural loss and to optimize the technique with respect to the Compression Factor. The listening tests showed maximum improvement in speech perception for a Compression Factor of 0.6, with an improvement of 9%-21% in the recognition scores for consonants and a significant reduction in response times.

  • Multi-band frequency Compression for sensorineural hearing impairment
    2009 16th International Conference on Digital Signal Processing, 2009
    Co-Authors: Pandurangarao N Kulkarni, Prem C Pandey, Dakshayani S Jangamashetti
    Abstract:

    Sensorineural hearing loss is associated with widening of the auditory filters, leading to increased spectral masking and degraded speech perception. Multi-band frequency Compression can be used for reducing the effect of spectral masking. The speech spectrum is divided into a number of bands and spectral samples in each of these bands are compressed towards the band center, by a constant Compression Factor. In the present study, we have investigated the effectiveness of the scheme for different Compression Factors, in improving the speech perception. Evaluation of the scheme using the modified rhyme test showed maximum improvement in recognition scores for Compression Factor of 0.6: about 17 % for the normal-hearing subjects under simulated hearing loss, and 6–21 % for the subjects with moderate to severe sensorineural hearing loss.

Horacio Soto-ortiz - One of the best experts on this subject based on the ideXlab platform.

  • Polarization dependence of non-linear gain Compression Factor in semiconductor optical amplifier.
    Optics express, 2008
    Co-Authors: Severine Philippe, A. Louise Bradley, Ramon Maldonado-basilio, Frederic Surre, Brendan F. Kennedy, Pascal Landais, Horacio Soto-ortiz
    Abstract:

    We investigate the power and the polarization dependence of the intraband dynamics in a bulk semiconductor optical amplifier using both a 2.5-ps pump-probe experimental set-up in contra-propagation and a theoretical model. Our model is based on the rate equations and takes into account the polarization dependence of the gain. By comparing experimental and computational results we are able to highlight the dependences of the intraband dynamics and to extract the non-linear gain Compression Factor as a function of both pulse energy and polarization of the injected pulses.