Numerical study of a stochastic particle algorithm solving a multidimensional population balance model for high shear granulation

This paper is concerned with computational aspects of a multidimensional population balance model of a wet granulation process. Wet granulation is a manufacturing method to form composite particles, granules, from small particles and binders. A detailed numerical study of a stochastic particle algorithm for the solution of a five-dimensional population balance model for wet granulation is presented. Each particle consists of two types of solids (containing pores) and of external and internal liquid (located in the pores). Several transformations of particles are considered, including coalescence, compaction and breakage. A convergence study is performed with respect to the parameter that determines the number of numerical particles. Averaged properties of the system are computed. In addition, the ensemble is subdivided into practically relevant size classes and analysed with respect to the amount of mass and the particle porosity in each class. These results illustrate the importance of the multidimensional approach. Finally, the kinetic equation corresponding to the stochastic model is discussed.     

On-Line Coupling of Separation Techniques to NMR

The hyphenation of chromatographic separation techniques with NMR spectroscopy is one of the most powerful and time-saving methods for the separation and structural elucidation of unknown compounds and molecular compositions of mixtures. Most of the routinely used NMR flow-cells have detection volumes between 40–180 μL for conventional separations with analytical columns, and the newest designs employ detection volumes in the order of 200 nL for capillary separations. The low flow rates used in capillary chromatography permit the use of deuterated solvents. Unequivocal structural assignment of unknown chromatographic peaks is possible by two-dimensional stopped-flow capillary HPLC-NMR experiments.     

Multiphasic Individual Growth Models in Random Environments

The evolution of the growth of an individual in a random environment can be described through stochastic differential equations of the form dY _t  = β(α − Y _t )dt + σdW _t , where Y _t  = h(X _t ), X _t is the size of the individual at age t, h is a strictly increasing continuously differentiable function, α = h(A), where A is the average asymptotic size, and β represents the rate of approach to maturity. The parameter σ measures the intensity of the effect of random fluctuations on growth and W _t is the standard Wiener process. We have previously applied this monophasic model, in which there is only one functional form describing the average dynamics of the complete growth curve, and studied the estimation issues. Here, we present the generalization of the above stochastic model to the multiphasic case, in which we consider that the growth coefficient β assumes different values for different phases of the animal’s life. For simplicity, we consider two phases with growth coefficients β ₁ and β ₂. Results and methods are illustrated using bovine growth data.     

Application of direct on-line coupling of HPLC and SFC with 1HNMR spectroscopy for the investigation of monomeric acrylates

The separation of monomeric acrylates was performed with High Performance Liquid Chromatography (HPLC) and Supercritical Fluid Chromatography (SFC). A direct on-line structural assignment of all compounds by continuous-flow ¹HNMR spectroscopy is possible with both separation techniques. The direct SFC-NMR coupling offers the advantage that the recorded continuous-flow ¹HNMR spectrum is not obscured by solvent signals.     

Application of high-performance liquid chromatography-nuclear magnetic resonance coupling to the identification of limonoids from mahogany tree (Switenia macrophylla, Meliaceae) by stopped-flow 1D and 2D NMR spectroscopy

Separation and characterization of limonoids from Switenia macrophylla (Meliaceae) by HPLC-NMR technique has been described. Analyses were carried out using reversed-phase gradient HPLC elution coupled to NMR (600 MHz) spectrometer in stopped-flow mode. Separated peaks were collected into an interface unit prior to NMR measurements, which were performed with suppression of solvent signals by shaped pulses sequences. Structure elucidation of the limonoids was attained by data obtained from 1H NMR, TOCSY, gHSQC and gHMBC spectra without conventional isolation that is usually applied in natural products studies.     

Application of direct on-line coupling of HPLC and SFC with 1HNMR spectroscopy for the investigation of monomeric acrylates

The separation of monomeric acrylates was performed with High Performance Liquid Chromatography (HPLC) and Supercritical Fluid Chromatography (SFC). A direct on-line structural assignment of all compounds by continuous-flow ¹HNMR spectroscopy is possible with both separation techniques. The direct SFC-NMR coupling offers the advantage that the recorded continuous-flow ¹HNMR spectrum is not obscured by solvent signals.Dedicated to Professor Dr. H. Kriegsmann on the occasion of his 70th birthday     

Structure Identification of Aporphine Alkaloids by On‐Line Coupling of HPLC‐NMR with Loop Storage

The potential of coupling HPLC separation methodology to on‐line high resolution nuclear magnetic resonance (NMR) spectroscopy has been demonstrated with a mixture of nine aporphine alkaloids. A loop storage procedure after separation has facilitated the identification of closely eluted peaks (α = k₂/k₁ = 1.01 and Δv = 0.37 min = 367 μL). These were collected off‐line and identified by a 1D ¹H NMR spectrum. For this purpose an automated procedure has been implemented which includes the use of shaped pulses, multiple solvents suppression and ¹³C satellite suppression of acetonitrile.     

Characterization of the aromatic composition of some liquid foods by nuclear magnetic resonance spectrometry and liquid chromatography with nuclear magnetic resonance and mass spectrometric detection

This paper describes the first application of NMR spectroscopy and LC-NMR/MS to the direct analysis of the aromatic composition of beer, grape juice and a wine phenolic extract. NMR spectroscopy provides non-invasive information on the overall aromatic profile and enables the identification of some compounds. However, a more comprehensive assignment is hindered by the low peak intensity and strong signal overlap in the low-field spectral region, as well as by the inherent lack of scalar coupling information for many aromatic compounds present. LC-NMR/MS can overcome these problems and is shown to aid significantly in the identification of aromatic compounds composing all samples analyzed. Some examples are the identification of several cinnamic acids (e.g. p-coumaric, trans-coutaric and trans-caftaric) in grape juice, the identification of 2-phenylethanol, tyrosol and tryptophol in beer and the detection of phenolics such as catechin, epicatechin, trans-resveratrol, tyrosol and caffeic acid in the wine extract.