Simultaneous Determination of Iron,Copper, and Cadmium by Adsorptive Stripping Voltammetry in the Presence of Thymolphthalexone

A novel, sensitive and selective adsorptive stripping procedure for simultaneous determination of iron, copper and cadmium is presented. The method is based on the adsorptive accumulation of thymolphthalexone (TPN) complexes of these elements onto a hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan using differential pulse modulation. The influences of control variables on the sensitivity of the proposed method for the simultaneous determination of iron, copper and cadmium were studied using the Derringer desirability function. The optimum analytical conditions were found to be TPN concentration of 2.0 μM, pH of 9.5, and accumulation potential at ?0.4 V vs. Ag/AgCl with an accumulation time of 60 s. The peak currents are proportional to the concentration of iron, copper and cadmium over the 1–80, 0.5–100 and 1–100 ng mL^?1 ranges with detection limits of 0.5, 0.4 and 0.9 ng mL^?1_, respectively. The R.S.D. at a concentration level of 20 ng mL^?1 of iron, copper and cadmium were 2.5%, 0.9% and 1.5% (n=6), respectively. The procedure was applied to the simultaneous determination of iron, copper and cadmium in the tap water and some synthetic samples with satisfactory results.     

Effect of counterions on the activity of lipase in cationic water-in-oil microemulsions

This paper delineates how the different counterions affect the physicochemical properties of the aqueous aggregates and thereby the lipase activities at the interface of cationic water-in-oil microemulsions. To this end, we have synthesized a series of cetyltrimethylammonium-based surfactants, 1-14, having aliphatic, aliphatic with aromatic substitution at the alpha position, and aromatic carboxylate anion as the counterion. The physicochemical characterizations of these aqueous aggregates were done by conductometric, tensiometric, fluorometric techniques to determine counterion binding (beta), critical micelle concentration (cmc), and micropolarity at the microenvironment. It has been found that the activity of lipase mainly increases with hydrophobicity (which is directly proportional to the counterion binding (beta) of the surfactant) of the counterion and reaches a maximum when the beta value is around 0.5. Increase in hydrophobicity as well as beta leads to the attachment of more counterions at interface resulting in enhancement of interfacial area. Consequently, the enzyme may attain flexible secondary conformation at the augmented surface area and also allow larger population of substrates and enzyme molecules at the interface leading to the enhancement in lipase activity. After an optimum value of beta, further increase probably produces a steric crowding at the interface, hindering the smooth occupancy of enzyme and the substrate in this region leading to decrease of enzyme activity, while molecular surface area of the counterion did not show any virtual influence on the lipase activity. Thus, the variation in the counterion structure and hydrophobicity plays a crucial role in modulating the lipase activity.     

Mass transfer enhancement by longitudinal vortices

From numerical and experimental investigations it has been recently established that convective heat transfer can be dramatically enhanced by the generation of longitudinal vortices in the flow. The phenomenological similarity between heat and mass transfer suggests that longitudinal vortices should increase also mass transfer. The mixing between two parallel streams of two components in a rectangular channel with and without a pair of rectangular winglets as vortex generators has been numerically investigated. The results show that one pair of vortex generators can increase the global mixing by more than 50 for laminar flow. This global mixing has been defined as the sum of the square of the differences of concentrations.     

Spectroscopic studies on nanodispersions of CdS, HgS, their core-shells and composites prepared in micellar medium

CdS is a large band gap material compared to HgS. Both are interesting from academic and technological points of view. The nanodispersions (colloids) of CdS and HgS as well their core-shell products and composites (co-colloids) were prepared by varied modes of precursor addition in micellar solution of cationic surfactant cetyltrimethylammonium bromide (CTAB). The prepared dispersions were studied by spectroscopic and electron microscopic techniques.     

Complex Harmonic-Oscillator Basis for the Relativistic Three-Body Problem

A complex harmonic-oscillator basis is employed for the three-body problem obeying S ₃-symmetry. Unlike a real basis it generates an additional quantum number (N _a ), in addition to the standard principal quantum number (N), and thus facilitates a more quantitative S ₃-classification of the various states than is usually possible. It is shown that certain bilinear forms with definite S ₃-symmetry properties, which can be constructed out of the linear harmonic-oscillator operators (a, a ^†) satisfy several uncoupled sets of SO(2, 1) algebras with spectra bounded from below. It is also briefly indicated how this S ₃-formalism can be adapted to the core structure of a more general relativistic three-particle system with unequal-mass kinematics through an appropriate choice of internal variables. Received May 11, 1994; revised November 3, 1994; accepted for publication November 23, 1994     

Deduction of generalised Kirchhoff's Laws from the basic principles of electromagnetism

The deduction of the so well-renowned and established Laws of Kirchhoff relating to the currents flowing in a network, which are considered to be almost axiomatic in electrical engineering sciences, seems to be preposterous and non-sensical at first sight. However, on a closer examination it will appear that these laws are based on two principles, viz, the steady-state condition under which accumulation of free electrical charge is precluded, and, the experimentalOhm's Law, which propounds a linear relation between the difference of potential across a conductor and the total current flowing through the same. But, there are two things, which are normally overlooked. The conductors inKirchhoff's Laws are “wires”, which are one-dimensional lines, and theOhm's Law is the macroscopicOhm's Law for total currents applied to these lumped resistors. Strictly speaking, the “Laws” are to be deduced from the more fundamental electromagnetic equations for continuous media and the microscopicOhm's Law. It is to be noted that theKirchhoff Nodal Law is but a consequence of the steady state condition derivable from these basic equations, viz, the current-density is divergence-free. For a continuous medium, what the form of theKirchhoff's Laws will be, is difficult to guess unless deduced from the basic equations. Once these are established from the basic equations of electromagnetism for a continuous medium, the usual form ofKirchhoff's Laws will follow as corollary of the general case, as has been shown here.     

Oxidation of naphthalene and phenanthrene by pyridinium fluorochromate (PFC)—a kinetic and mechanistic study

The kinetics of the oxidation of naphthalene and phenanthrene by pyridinium fluorochromate, C₅H₅NHCrO₃F, PFC, has been studied. The main product of the oxidation is the corresponding quinone. While each oxidation, studied in aqueous acetic acid (80–95%, v/v) medium, is first order with respect to the oxidant, the rate is almost independent of the substrate concentration. The reactions are catalyzed by acid, the acid-catalyzed reactions being very fast, which precluded determination of their order in acid medium. The kinetic isotope effect, k_H/k_D is 5.50 at 303 K for naphthalene. The reaction does not induce polymerization of acrylonitrile. The effects of temperature and solvent compositions were studied and activation parameters evaluated. Probable mechanisms are discussed.