New methods for trace titanium determination by adsorptive preconcentration voltammetry with pyrocatechol violet

New sensitive stripping voltammetric procedures for trace measurements of titanium in various samples are reported. The first method is based on the interfacial accumulation of the titanium-pyrocatechol violet complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed complex. The limit of detection is 0.55 nmol/L titanium after a 30 s collection with a stirred solution at pH 4.9. The procedure is extremely selective with respect to other metals and has been applied in analyzing various samples. Based on this, a catalytic method involving the chlorate ion was developed and the sensitivity was enhanced by more than an order of magnitude. In this way, analysis for Ti in aqueous solutions at the picomolar (part per trillion) level is possible.     

The Locally Conservative Galerkin (LCG) Method — a Discontinuous Methodology Applied to a Continuous Framework

This paper presents a comprehensive overview of the element-wise locally conservative Galerkin (LCG) method. The LCG method was developed to find a method that had the advantages of the discontinuous Galerkin methods, without the large computational and memory requirements. The initial application of the method is discussed, to the simple scalar transient convection-diffusion equation, along with its extension to the Navier-Stokes equations utilising the Characteristic Based Split (CBS) scheme. The element-by-element solution approach removes the standard finite element assembly necessity, with an face flux providing continuity between these elemental subdomains. This face flux provides explicit local conservation and can be determined via a simple small post-processing calculation. The LCG method obtains a unique solution from the elemental contributions through the use of simple averaging. It is shown within this paper that the LCG method provides equivalent solutions to the continuous (global) Galerkin method for both steady state and transient solutions. Several numerical examples are provided to demonstrate the abilities of the LCG method.     

Chemical force microscopy investigation of phosphate adsorption on the surfaces of iron(III) oxyhydroxide particles

Phosphate-modified AFM tips were prepared by the deposition of self-assembled monolayers (SAMs) of bis(11-thioundecyl) phosphate on Au-coated silicon nitride cantilevers. The properties of the PO(2)H-terminated SAMs were investigated by studying the pH-dependent force interactions of the tips with phosphate- and carboxylic acid-terminated SAM control surfaces. The PO(2)H functional groups had a pK(a) of approximately 5.0. A chemical force microscopy (CFM) study was conducted on the interactions between the probes and the surfaces of hydrous ferric oxide particles prepared in our laboratory by hydrolytic precipitation from FeCl(3). The forces between PO(2)H probes and the hydrous ferric oxide surfaces were seen to exhibit a strong pH dependence, with maximum attractive forces occurring for pH values between 5 and 8. The effects of postprecipitation of the hydrous ferric oxide colloids with orthophosphate, H(2)PO(4)(-), dimethylphosphate, (CH(3)O)(2)PO(2)H (DMP), and tannic acid (TA) on the adhesive interactions between the PO(2)H tips and the solids were also investigated. Attenuated total reflectance infrared spectroscopy (ATR-IR) was used to verify the presence of surface-adsorbed species and zeta potentiometric measurements to determine surface charge on the colloids. We show that the method of chemical force titration using phosphate-terminated tips can differentiate between these various colloids and that it shows promise as a general method for studying this environmentally important class of compounds.