Physical Experimental Parameters Research Articles

Theoretical formulation of the distribution function of critical nuclei under precipitation polymerization conditions

Precipitation Polymerization (Pre-Poly) can be considered a nucleation and growth process in which complex and high molecular weight branched polymers are involved. From an experimental point of view, it is well-known that under Pre-Poly conditions the phase transition (nucleation) occurs in the first minutes of polymerization, and then a long growth stage is observed in which the critical nuclei simultaneously grow until reaching a highly monodisperse distribution of microspheres (characteristic mechanism of binodal decomposition). The high rate at which nucleation and growth processes usually take place when radical polymerization (extremely high polymerization rate) under Pre-Poly conditions is used, makes it very difficult to study experimentally some aspects of these processes, such as the size and concentration of critical nuclei, among others. Based on the thermodynamic principles of Pre-Poly, this analytical paper covers for the first time, to the best of our knowledge, the theoretical formulation of the distribution function of critical nuclei under Pre-Poly conditions. In addition, a simple empirical method to calculate the concentration of critical nuclei was also developed using only three global, physical experimental parameters, and good agreement was found between empirical and theoretical calculations.

Thermodynamic study and spectrophotometric determination of cefixime trihydrate in pure form and pharmaceutical tablets using batch and normal flow injection analysis

This study aimed at developing pectrophotometric methods for the determination of Cefixime Trihydrate [CFT] by simple, sensitive batch and flow-injection analysis in its purest form and tablet formulations. These developed methods were based on an oxidative coupling reaction of CFT with thaimine hydrochloride in the presence of a basic medium and using potassium ferricyanuide as an oxidant to produce a stable water-soluble, intense orange dye with a maximum absorption at 440 nm. Beer's law was followed over the concentration range [2.5-75 and 10-400 µg.mL-1] of CFT with limits of detection of 0.7223 and 2.6145 µg.mL-1 of CFT for batch and FIA methods, respectively. The average sample throughput for the FIA was 68 h-1. The effects of various chemical and physical experimental parameters on the development and stability of the colored product were carefully investigated. CFT estimated in commercial tablets forms was successfully applied using these methods, in which the results were in good agreement with those produced using the official procedure. Thermodynamic parameters, including the free energy changes [∆G], enthalpy [∆H] and entropy [∆S] were determined at different temperatures for the reaction product.

DETERMINATION OF PHENYLEPHRINE HYDROCHLORIDE IN PHARMACEUTICAL PREPARATIONS USING SPECTROPHOTOMETRIC METHOD

Objective: A simple and sensitive spectrophotometric method has been presented for the determination of phenylephrine hydrochloride by coupling reaction with diazotized sulfacetamide sodium.
 Methods: The method is based on the diazotization reaction of sulfacetamide sodium with sodium nitrite in the presence of hydrochloric acid to form diazonium salt, which is coupled with the drug in alkaline medium to form azo dye, showing absorption maxima at 425 nm.
 Results: Calibration plot was linear over the concentration range of 2–24 μg/mL and detection limit of 0.278 μg/mL with a correlation coefficient of 0.9929. All different chemical and physical experimental parameters affecting on the development and stability of the colored product were carefully studied.
 Conclusions: The proposed method was successfully applied to the determination of phenylephrine in nasal drops with good precision and sensitivity.

A Reynolds equation modelling Coriolis force effects on chemical mechanical polishing

A Reynolds equation modelling chemical mechanical polishing in cylindrical polar coordinates is derived. Coriolis force effects are included in the derivation of the model equation. The main effect of the Coriolis force is to increase the magnitude of the peak pressure. A model for the peak pressure is given by max|p/patm|≈κ/ϵ where p is the pressure, patm is atmospheric pressure, κ=5×10−8 is a constant and ϵis a ratio of the thin film height to the height of the Ekman boundary layer. The value of ϵis obtained through numerical experimentation. Using the physical experimental parameters we show that for Newtonian fluids ϵ=O(10−5).

Determination of Doxycycline Hyclate by Batch and Reverse Flow Injection Analysis Based on the Oxidative Coupling Reaction with 3-Methyl-2-benzothiazolinone Hydrazone hydrochloride (MBTH)

New, simple and sensitive batch and reverse FIA spectrophotometric methods for the determination of doxycycline hyclate in pure form and in pharmaceutical preparations were proposed. These methods based on oxidative coupling reaction between doxycycline hyclate and 3-methylbenzothiazolinone-2-hydrazone hydrochloride (MBTH) in the presence ammonium ceric sulfate in acidic medium, to form green water-soluble dye that is stable and has a maximum absorbance at 626 nm. A calibration graph shows that a Beer's law is obeyed over the concentration range of 1-80 and 0.5-110 ?g.mL-1 of DCH for the batch and rFIA respectively with detection limit of 0.325 ?g.mL-1 of DCH for r-FIA methods. All different chemicals and physical experimental parameters affecting the development and stability of the colored product were carefully studied. The proposed methods were successfully applied for the determination of DCH in pharmaceutical preparations.

Ground based testing of space tether deployment using an air bearing inclinable turntable

This paper discusses the development of a ground based experimental environment that can mimic the deployment dynamics of tethered satellites in orbit. The setup consists of an air-bearing inclinable turntable, whose inclination and rotation rate can be adjusted individually. Appropriate scaling factors are developed for the various forces acting on the daughter satellite as well as for physical experimental parameters including the length of the tether, the mass of the daughter satellite, the deployment speed and the tension along the tether. The scaling factors are used to compare the behaviour of the tethered system in the experiment to that in orbit.

Determination of Doxycycline Hyclate by Batch and Reverse Flow Injection Analysis Based on the Oxidative Coupling Reaction with 3-Methyl-2-benzothiazolinone Hydrazone hydrochloride (MBTH)

New, simple and sensitive batch and reverse FIA spectrophotometric methods for the determination of doxycycline hyclate in pure form and in pharmaceutical preparations were proposed. These methods based on oxidative coupling reaction between doxycycline hyclate and 3-methylbenzothiazolinone-2-hydrazone hydrochloride (MBTH) in the presence ammonium ceric sulfate in acidic medium, to form green water-soluble dye that is stable and has a maximum absorbance at 626 nm. A calibration graph shows that a Beer's law is obeyed over the concentration range of 1-80 and 0.5-110 ?g.mL-1 of DCH for the batch and rFIA respectively with detection limit of 0.325 ?g.mL-1 of DCH for r-FIA methods. All different chemicals and physical experimental parameters affecting the development and stability of the colored product were carefully studied. The proposed methods were successfully applied for the determination of DCH in pharmaceutical preparations.

Two-dimensional metal-insulator transition as a strong localization induced crossover phenomenon

Low-disorder and high-mobility 2D electron (or hole) systems undergo an apparent metal-insulator-transition (MIT) at low temperatures as the carrier density (n) is varied. In some situations, the 2D MIT can be caused at a fixed low carrier density by changing an externally applied in-plane magnetic field parallel to the 2D layer. d\rho/dT changes its sign at some nonuniversal sample-dependent critical carrier density n_c separating an effective 2D metal (d\rho/dT >0) for n>n_c from an effective 2D insulator (d\rho/dT<0) for n<n_c. We study the 2D MIT phenomenon as a possible strong localization induced crossover process controlled by the Ioffe-Regel criterion, k_F l=1. Calculating the quantum mean free path (l) in the effective metallic phase from a realistic transport theory including disorder scattering effects, we solve the integral equation defined by the Ioffe-Regel criterion to obtain the nonuniversal critical density n_c as a function of the applicable physical experimental parameters including disorder strength, in-plane magnetic field, spin and valley degeneracy, background dielectric constant and carrier effective mass, and temperature. The key physics underlying the nonuniversal parameter dependence of the n_c is the temperature and density dependence of the Coulomb disorder. Our calculated results for the crossover n_c appear to be in qualitative and semi-quantitative agreement with the available experimental data in different 2D semiconductor systems lending credence to the possibility that the apparent 2D MIT signals the onset of the strong localization crossover in disordered 2D systems. We provide some results for graphene where a low-temperature 2D MIT becomes possible in the presence of intervalley scattering. We also provide an extensive comparison with the theoretical results obtained on the basis of 2D MIT being considered as a percolation transition.

Batch and Flow-Injection Spectrophotometric Determination of Procaine HCl in Pharmaceutical Preparations Via Using Diazotization and Coupling Reaction

Simple and sensitive batch and Flow-injection spectrophotometric methods for the determination of Procaine HCl in pure form and in injections were proposed. These methods were based on a diazotization reaction of procaine HCl with sodium nitrite and hydrochloric acid to form diazonium salt, which is coupled with chromatropic acid in alkaline medium to form an intense pink water-soluble dye that is stable and has a maximum absorption at 508 nm. A graphs of absorbance versus concentration show that Beer’s law is obeyed over the concentration range of 1-40 and 5-400 µg.ml-1 of Procaine HCl, with detection limits of 0.874 and 3.75 µg.ml-1 of Procaine HCl for batch and FIA methods respectively. The FIA average sample throughput was 70 h-1. All different chemical and physical experimental parameters that affecting on the development and stability of the colored product were carefully studied and the proposed methods were applied satisfactorily for the determination of Procaine HCl in an injections samples using the standard addition method.

Batch and Flow-Injection Spectrophotometric Determination of Procaine HCl in Pharmaceutical Preparations Via Using Diazotization and Coupling Reaction

Simple and sensitive batch and Flow-injection spectrophotometric methods for the determination of Procaine HCl in pure form and in injections were proposed. These methods were based on a diazotization reaction of procaine HCl with sodium nitrite and hydrochloric acid to form diazonium salt, which is coupled with chromatropic acid in alkaline medium to form an intense pink water-soluble dye that is stable and has a maximum absorption at 508 nm. A graphs of absorbance versus concentration show that Beer’s law is obeyed over the concentration range of 1-40 and 5-400 µg.ml-1 of Procaine HCl, with detection limits of 0.874 and 3.75 µg.ml-1 of Procaine HCl for batch and FIA methods respectively. The FIA average sample throughput was 70 h-1. All different chemical and physical experimental parameters that affecting on the development and stability of the colored product were carefully studied and the proposed methods were applied satisfactorily for the determination of Procaine HCl in an injections samples using the standard addition method.

Batch and Flow-Injection Spectrophotometric Determination of Thymol Using Procaine Hydrochloride as a New Chromogenic Reagent

New, simple and sensitive batch and Flow-injecton spectrophotometric methods for the determination of Thymol in pure form and in mouth wash preparations have been proposed in this study. These methods were based on a diazotization and coupling reaction between Thymol and diazotized procaine HCl in alkaline medium to form an intense orange-red water-soluble dye that is stable and has a maximum absorption at 474 nm. A graphs of absorbance versus concentration show that Beer’s law is obeyed over the concentration range of 0.4-4.8 and 4-80 µg.ml-1 of Thymol, with detection limits of 0.072 and 1.807 µg.ml-1 of Thymol for batch and FIA methods respectively. The FIA procedure sample throughput was 80 h-1. All different chemical and physical experimental parameters that affecting on the development and stability of the colored product were carefully studied and the proposed methods were successfully applied to the determination of Thymol in mouth wash preparations.

Batch and Flow-Injection Spectrophotometric Determination of Thymol Using Procaine Hydrochloride as a New Chromogenic Reagent

New, simple and sensitive batch and Flow-injecton spectrophotometric methods for the determination of Thymol in pure form and in mouth wash preparations have been proposed in this study. These methods were based on a diazotization and coupling reaction between Thymol and diazotized procaine HCl in alkaline medium to form an intense orange-red water-soluble dye that is stable and has a maximum absorption at 474 nm. A graphs of absorbance versus concentration show that Beer’s law is obeyed over the concentration range of 0.4-4.8 and 4-80 µg.ml-1 of Thymol, with detection limits of 0.072 and 1.807 µg.ml-1 of Thymol for batch and FIA methods respectively. The FIA procedure sample throughput was 80 h-1. All different chemical and physical experimental parameters that affecting on the development and stability of the colored product were carefully studied and the proposed methods were successfully applied to the determination of Thymol in mouth wash preparations.

Chitosan beads as barriers to the transport of azo dye in soil column

The development of chitosan-based materials as useful adsorbent polymeric matrices is an expanding field in the area of adsorption science. Although chitosan has been successfully used for the removal of dyes from aqueous solutions, no consideration is given to the removal of dyes from contaminated soils. Therefore this study focuses on the potential use of chitosan as an in situ remediation technology. The chitosan beads were used as barriers to the transport of a reactive dye (Reactive Black 5, RB5) in soil column experiments. Batch sorption experiments, kinetic and equilibrium, were performed to estimate the sorption behavior of both chitosan and soil. The chitosan beads were prepared in accordance with published literature and a synthetic soil was prepared by mixing quantities of sand, silt and clay. The synthetic soil was classified according to British Standards. Calcium chloride was used as tracer to define transport rates and other physical experimental parameters. Dye transport reaction parameters were determined by fitting dye breakthrough curves (BTCs) to the HYDRUS-1D version 4.xx software. Fourier Transform-Infra Red (FT-IR) spectroscopy was used to reveal the sorption mechanism. The study showed that chitosan exhibited a high sorption capacity (S(max)=238 mg/g) and pseudo-first sorption rate (k(1)=1.02 h(-1)) coupled with low swelling and increased retardation for the azo dye tested. Thus it has potential as a Permeable Reactive Barrier (PRB) for containment and remediation of contaminated sites.