Application of cloud point extraction technique to preconcentration and spectrophotometric determination of free chlorine in water samples

A rapid, selective, and sensitive cloud point extraction process using mixed micelle of a nonionic surfactant Triton X-114 and an anionic surfactant, SDS, to extract chlorine from aqueous solution was investigated. The method is based on the color reaction of chlorine with N,N-diethyl-p-phenylenediamine (DPD) in phosphate buffer media and cloud point extraction of the produced dye. Various factors and extraction and reaction conditions such as surfactant concentration and reagent concentration were studied and the analytical characteristics of the method (e.g. limit of detection, linear range, preconcentration, and improvement factors) were obtained. Linearity was obeyed in the range of 3.0–450 ng/mL of chlorine and the detection limit of the method was 1.0 ng/mL. The interference effects of some cations and anions were also tested. The proposed method was successfully applied to the determination of free chlorine in drinking, river, well and pool swimming water samples.     

Numerical modelling of the entrainment of particles in inviscid supersonic flow

The interaction between particles situated in close proximity and moving at supersonic speeds is investigated computationally. The simplest case of the motion of a single particle travelling behind a lead particle is used to elucidate the role of aerodynamic forces in the motion of a group of particles. The effect of the following parameters on the drag and lift forces acting on each of two particles of equal diameter in proximity is investigated: the free-stream Mach number, and the axial and lateral displacements of the trailing particle. The two-dimensional flow field is numerically simulated using an unsteady Euler CFD code to find the steady-state drag and lift coefficients for both particles. Three static zones of aerodynamic influence in the wake of the lead particle are identified, which are denoted as the entrainment, lateral attraction, and ejection zones. A non-dimensional representation of the zones of influence is given. It is shown that the dynamic entrainment of particles can occur even when the path of the trailing particle originates outside the entrainment and lateral attraction zones.     

Simplified modeling of blast waves from metalized heterogeneous explosives

The detonation of a metalized explosive generates a complex multiphase flow field. Modeling the subsequent propagation of the blast front requires a detailed knowledge of the metal particle dynamics and reaction rate. Given the uncertainties in modeling these phenomena, a much simpler, 1D compressible flow model is used to illustrate the general effects of secondary energy release due to particle reaction on the blast front properties. If the total energy release is held constant, the blast pressure and impulse are primarily dependent on the following parameters: the proportion of secondary energy released due to afterburning, the rate of energy release, the location the secondary energy release begins, and the range over which it occurs. Releasing the total energy over a longer time period in general reduces the peak blast overpressure at a given distance. However, secondary energy release reduces the rate of decay of the shock pressure, increases the local gas temperature and hence increases the velocity of the secondary shock front. As a result, for certain values of the above parameters, the peak blast impulse may be increased by a factor of about two in a region near the charge. The largest augmentation to the near-field peak impulse results when the secondary energy is released immediately behind the shock front rather than uniformly within the combustion products.     

Aryldiazonium silica sulfates as efficient reagents for Heck-type arylation reactions under mild conditions

An efficient and straightforward procedure for Heck-type arylation reactions was studied using aryldiazonium silica sulfates and olefins in the presence of a catalytic amount of Pd(OAc)₂. These reactions were carried out in water at room temperature without using a base or additional ligands. The use of a non-toxic solvent, a simple and clean work-up, short reaction times, and good yields are advantages of this method.     

Q-Switching Pulse Generation with Thulium-Doped Fiber Saturable Absorber

Q-switched pulsed laser systems operating in the eye-safe wavelength region （λ〉 1.4 μm） are promis- ing for applications such as light detection and ranging （lidar）, differential absorption lidar, optical communi- cation, sensor and instrumentations. Fiber lasers are particularly attractive for such applications due to the fact that the beam quality can be independent of output power and they can be robustly engineered. There is an increasing interest in Q-switched erbium- doped fiber lasers （EDFLs）, which can be generated by using either active or passive techniques. Com- pared with the actively Q-switched ones, passively Q- switched EDFLs have attracted much attention for their advantages of compactness, low cost, flexibility and simplicity of design. Different kinds of saturable absorbers, such as the transition metal-doped crys- tals and semiconductor quantum-well structures, have been applied to realize Q-switched EDFLs.How- ever, when they are used in the laser cavity, additional alignment devices, such as lens, mirrors or U-bench units, have to be applied. This may increase the in- sertion loss and the complexity of the laser cavity.     

Simultaneous Determination of Nitrophenol Isomers at Multi-Walled Carbon Nanotube-β-Cyclodextrin-Poly (Diphenylamine) Composite Modified Glassy Carbon Electrode

Russian Journal of Electrochemistry - Nitrophenol (NP) isomers are toxic for human, animals and plants. Therefore determination of them in environment is very urgent and important. In this paper,...     

Green Sample Preparation Based on Directly Suspended Droplet Microextraction using Deep Eutectic Solvent for Ultra-Trace Quantification of Nitroaromatic Explosives by High Performance Liquid Chromatography

Journal of Analytical Chemistry - In the present study, a simple and efficient directly suspended-solidified floating organic droplet microextraction using deep eutectic solvent in combination with...