Pushing the detectability of voltammetry: how low can we go?

The coupling of adsorptive accumulation with catalytic reactions results in remarkably low (sub-picomolar) detection limits. This review assesses various strategies for attaining such dual-amplification effects, that lead to the most sensitive voltammetric technique, adsorptive-catalytic stripping voltammetry (AdCtSV).     

Use of pH electrode for precipitation titration analysis: Theory and practice

A theoretical model for the potentiometric analysis of precipitation titrations using a pH electrode has been developed and tested. The new analytical method is possible by introducing a mediator which must be a weak acid and must be able to form an insoluble salt with a cation (a titrant). Theoretical expressions of pH, as well as the concentrations of all other species, were derived and solved numerically using bisection method. Among the various factors that influence pH during the titration, concentrations of the mediator and initial values of pH were proved to be very critical. The experimental potentiometric titration curves agree well with those predicted from the theoretical model. Crossing point method was adopted to determine an equivalence point from the titration curves. The method is tested using a known system of chloride determination. Among the several mediators tested (bisulfite, chromate, phosphate, cyanide, arsenate and EDTA), phosphate yielded the best results with an error of 0.1%; bisulfite, chromate and arsenate yielded comparably good results with an error of 0.3∼0.5%, but cyanide and EDTA yielded unsatisfactory results. The optimum mediator concentration found to be in a range of 1–2 mM.     

A one-parameter formula for estimating the Λ well depth

A one parameter, semi-empirical formula for Λ-binding energy of heavy hypernuclei in the inverse powers of core mass number (A _c) has been developed in the framework of the folding model. Unlike similar calculations reported by other authors (Deloff 1971; Daskaloyanniset al 1985), we are able to take into account the effect arising from the difference in the number of protons and neutrons of the core nuclei having same mass number. The radius and diffuseness are parametrized using the experimentally known charge density data of a fairly large number of medium and heavy nuclei. The well depth parameter (i.e. Λ-binding energy in infinite nuclear matter) in the formula is obtained from a fit to theB _Λ data of _Λ ²⁸ Si, _Λ ⁴⁰ Ca, _Λ ⁵¹ V and _Λ ³⁹ Y. Using the original Λ-nucleus potential, theB _Λ of ground and the experimentally known excited states of these hypernuclei have also been calculated by solving numerically the two-body Schrödinger equation. The agreement with the experimental data is satisfactory.