Physical-Chemical Characterization and Polymorphism Determination of Two Nimodipine Samples Deriving from Distinct Laboratories

Knowing the characteristics of raw materials in pharmaceutical practice is both important and useful. Firstly, evaluating the physical-chemical properties of the substances that will be used must be the primary step for quality control in the pharmacy industry. This work aims at analyzing the physical-chemical characteristics of two nimodipine samples I and II derived from distinct laboratories through thermal analysis (DSC and TG/DTG), HPLC, crystallography, and microscopy. Thermal analysis showed that sample II was more unstable than I. Morphological differences concerning shape, size, and crystallinity of particles were visualized by scanning electron microscopy (SEM) and X-ray powder diffraction. To sum up, the techniques used in this study can be said to have been efficient in the characterization and evaluation of quality control of the raw material.     

Experimental investigations on the effects of asparagine and serine on the polymorphism of calcium carbonate

The present study investigated the effects of the amino acids asparagine and serine, as additives, on the polymorphic transformation of calcium carbonate (CaCO₃) within the concentration range of 25–100 ppm at 30 °C and pH 12. The structural composition and morphology of the samples prepared with and without additives were evaluated experimentally through X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) analysis. The XRD results showed that the calcite composition of CaCO₃ samples prepared with asparagine and serine reduced with increasing concentrations of both additives. SEM images showed that CaCO₃ prepared with asparagine and serine had three coexisting crystal forms: cubic-shaped calcite, spherical shaped vaterite, and needle-like aragonite crystals. Moreover, the addition of both additives separately was found to increase the average particle size and Brunauer–Emmett–Teller (BET) specific surface area of the crystals. Higher concentrations of serine and asparagine individually in the crystallization media resulted in a more negative zeta potential. Meanwhile, the thermal behavior, kinetics, and thermodynamics of the CaCO₃ crystals were simultaneously evaluated by means of by thermogravimetric analysis (TGA) coupled with Fourier transform infrared (FTIR) and mass spectrometry (MS). The master plots method combined with the Friedman method revealed that the decomposition of CaCO₃ prepared in pure media followed the contracting volume mechanism, R₃. Positive values of ΔH and ΔG were obtained for CaCO₃ decomposition.     

Separation and enrichment of gold(III) from environmental samples prior to its flame atomic absorption spectrometric determination

A simple and accurate method was developed for separation and enrichment of trace levels of gold in environmental samples. The method is based on the adsorption of Au(III)-diethyldithiocarbamate complex on Amberlite XAD-2000 resin prior to the analysis of gold by flame atomic absorption spectrometry after elution with 1 molL(-1) HNO3 in acetone. Some parameters including nitric acid concentration, eluent type, matrix ions, sample volume, sample flow rate and adsorption capacity were investigated on the recovery of gold(III). The recovery values for gold(III) and detection limit of gold were greater than 95% and 16.6 microgL(-1), respectively. The preconcentration factor was 200. The relative standard deviation of the method was <6%. The adsorption capacity of the resin was 12.3 mg g(-1). The validation of the presented procedure was checked by the analysis of CRM-SA-C Sandy Soil certified reference material. The presented procedure was applied to the determination of gold in some environmental samples.     

Effect of molecular weight and testing rate on adhesion property of pressure-sensitive adhesives prepared from epoxidized natural rubber

The dependence of peel strength and shear strength of epoxidized natural rubber (ENR 25)-based pressure-sensitive adhesive on molecular weight and rate of testing was investigated using coumarone-indene as the tackifying resin. Toluene and polyethylene terephthalate (PET) were used as the solvent and substrate respectively throughout the study. A SHEEN hand coater was used to coat the adhesive on the substrate at a coating thickness of 120 μm. All the adhesion properties were determined by a Llyod Adhesion Tester operating at different rates of testing. Result shows that peel strength and shear strength increases up to an optimum molecular weight of 6.5 × 10⁴ of ENR 25. For peel strength, the observation is attributed to the combined effects of wettability and mechanical strength of rubber at the optimum molecular weight, whereas for the shear strength, it is ascribed to the increasing amount of adhesive present in the coating layer which enhances the shear resistance of the adhesive. Peel strength and shear strength also increases with increase in rate of testing, an observation which is associated to the viscoeslastic response of the adhesive. Differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) study confirms the miscibility of tackifier and the ENR 25.     

Identifying Phase‐Dependent Electrochemical Stripping Performance of FeOOH Nanorod: Evidence from Kinetic Simulation and Analyte–Material Interactions

Metal hydroxide nanomaterials are widely applied in the energy and environment fields. The electrochemical performance of such materials is strongly dependent on their crystal phases. However, as there are always multiple factors relating to the phase‐dependent electrochemistry, it is still difficult to identify the determining one. The well‐defined crystal phases of α‐ and β‐FeOOH nanorods are characterized through the transmission electron microscopy by a series of rotation toward one rod, where the cross‐section shape and the growth direction along the [001] crystalline are first verified for 1D FeOOH nanostructures. The electrosensitivity of the two materials toward Pb(II) is tested, where α‐FeOOH performs an outstanding sensitivity whilst it is only modest for β‐FeOOH. Experiments via Fourier transform infrared spectroscopy, X‐ray absorption fine structure (XAFS), etc., show that α‐FeOOH presents a larger Pb(II) adsorption capacity due to more surficial hydroxyl groups and weaker Pb? O bond strength. The reaction kinetics are simulated and the adsorption capacity is found to be the determining factor for the distinct Pb(II) sensitivities. Combining experiment with simulation, this work reveals the physical insights of the phase‐dependent electrochemistry for FeOOH and provides guidelines for the functional application of metal hydroxide nanomaterials.