Column comparison and method development for the analysis of short‐chain carboxylic acids by zwitterionic hydrophilic interaction liquid chromatography with UV detection

Short‐chain carboxylic acids are relevant in pharmaceutical, food quality control, and biomedical analysis. In this study, 11 acids commonly found in drugs and in food products were selected. Wine was chosen as matrix for testing the method. The test compounds were used for comparing the selectivity of four 150 × 2.1 mm zwitterionic hydrophilic interaction LC (HILIC) columns (ZIC‐HILIC 5 μm, 200 Å, and 3.5 μm, 100 Å, ZIC‐pHILIC 5 μm, ZIC‐cHILIC 3 μm, 100 Å) while varying the conditions to optimize for low UV wavelength detection and achieve high sensitivity. Retention using potassium phosphate and ammonium carbonate as mobile‐phase components at pH 6.0, 7.5, and 8.5–8.9 was studied considering recent hypotheses on HILIC mechanism‐related with the Hofmeister series effect and ion hydration. An isocratic method with UV detection at 200 nm and mobile phase consisting of 75% acetonitrile and 10 mM potassium phosphate at pH 6.0 applied to a ZIC‐cHILIC column was found provisionally optimal and partially validated for the 11 analytes. Satisfactory results (R² from 0.9940 to >0.9999), and recoveries from 93–106% for all analytes evidenced the method as suitable for wine analysis. To the best of our knowledge, no previous study has reported on the direct ZIC‐HILIC separation and UV detection of the acids considered here in wine.     

Experimental investigation of the effect of initial fuel particle shape, size and bed temperature on devolatilization of single wood particle in a hot fluidized bed

Considerable amount of investigation on the subject of devolatilization of wood is found in the open literature. However, a systematic study of the effect of initial particle size and shape, and bed temperature on devolatilization time and char yield of wood in a hot fluidized bed is still missing. This paper attempts to fill this gap through a systematic experimental investigation to determine the devolatilization time and char yield of a typical woody biomass, “Casuarina equisetifolia” particles of different initial sizes and shapes at various fluidized bed temperatures. Experiments are conducted using 10, 15, 20, and 25 mm Casuarina wood particles of three shapes, namely, cube, cylinder, and sphere at bed temperatures of 1023, 1123, and 1223 K.It is found that the initial wood particle size has the strongest influence on devolatilization time followed by the shape of initial wood particle and the bed temperature. Correlation for devolatilization time (τ_d) as a function of initial wood particle size (d_eq), sphericity (?), and bed temperature (T_b), is developed using 573 experimental data points exhibiting a correlation coefficient of 0.96 and predictions falling well within a deviation band of ±20%. The predictions of the present correlation are compared with the predictions of the existing correlations in literature for conditions also out of the present study and the deviation is found to be ±30%.Char yield, defined as the ratio of the residual mass at the end of devolatilization process to the initial mass of the wood particle is found to be in the range of 9-14% for all sizes, shapes, and bed temperatures. Char yield does not depict any definite trend with the variation of initial particle size, shape and bed temperature.     

Why ultra high performance liquid chromatography produces more tailing peaks than high performance liquid chromatography, why it does not matter and how it can be addressed

The purpose of this study is to demonstrate, with experiments and with computer simulations based on a firm chromatographic theory, that the wide spread perception of that the United States Pharmacopeia tailing factor must be lower than 2 (T(f)<2) is questionable when using the latest generation of LC equipment. It is shown that highly efficient LC separations like those obtained with sub-2 μm porous and 2.7 μm superficially porous particles (UHPLC) produce significantly higher T(f)-values than the corresponding separation based on 3 μm porous particles (HPLC) when the same amount of sample is injected. Still UHPLC separations provide a better resolution to adjacent peaks. Expressions have been derived that describe how the T(f)-value changes with particle size or number of theoretical plates. Expressions have also been derived that can be used to scale the injection volume based on particle size or number of theoretical plates to maintain the T(f)-value when translating a HPLC separation to the corresponding UHPLC separation. An aspect that has been ignored in previous publications. Finally, data obtained from columns with different age/condition indicate that T(f)-values should be complemented by a peak width measure to provide a more objective quality measure.     

Analyser‐based tomography images of cartilage

Analyser‐based imaging expands the performance of X‐ray imaging by utilizing not only the absorption properties of X‐rays but also the refraction and scatter rejection (extinction) properties. In this study, analyser‐based computed tomography has been implemented on imaging an articular cartilage sample, depicting substructural variations, without overlay, at a pixel resolution of 3.6 µm.     

Double and negative reflection of cold atoms in non-Abelian gauge potentials

Atom reflection is studied in the presence of a non-Abelian vector potential proportional to a spin-1/2 operator. The potential is produced by a relatively simple laser configuration for atoms with a tripod level scheme. We show that the atomic motion is described by two different dispersion branches with positive or negative chirality. As a consequence, atom reflection shows unusual features, since an incident wave may split into two reflected ones at a barrier, an ordinary specular reflection, and an additional nonspecular one. Remarkably, the latter wave can exhibit negative reflection and may become evanescent if the angle of incidence exceeds a critical value. These reflection properties are crucial for future designs in non-Abelian atom optics.     

Deuteron energy of 15 MK in ultra-dense deuterium without plasma formation: Temperature of the interior of the Sun

Deuterons are released with kinetic energy up to 630 eV from ultra-dense deuterium as shown previously, by Coulomb explosions initiated by ns laser pulses at . With higher laser intensity at , the initial kinetic energy now observed by TOF-MS with variable acceleration energy is up to 1100 eV per deuteron. This indicates ejection of one deuteron by Coulomb repulsion from two stationary charges in the material. It proves a full kinetic energy release of 1260 eV or a deuteron temperature of 15 MK, similar to the temperature in the interior of the Sun. Plasma processes are excluded by the sharp TOF peaks observed and by the slow signal variation with laser intensity. Deuterons with even higher energy from multiple charge repulsion are probably detected. D + D fusion processes are expected to exist in the ultra-dense phase without plasma formation.     

An adaptive stochastic sequential quadratic programming with differentiable exact augmented lagrangians

Mathematical Programming - We consider solving nonlinear optimization problems with a stochastic objective and deterministic equality constraints. We assume for the objective that its evaluation,...     

A Diffuse-Interface Approach for Solid-State Dewetting with Anisotropic Surface Energies

Journal of Nonlinear Science - Exact variational integrators were exposed in the context of Lagrangian mechanics in Marsden and West (2001). These integrators sample the trajectories of holonomic...