Band 71, Heft 5

Synopsis : The influence of pressure on chemical equilibria in aqueous solutions and the parameters that influence such equilibria are reviewed in this work. Particular emphasis is given to equilibria in seawater, including mineral dissolution, weak acid dissociation and metal ion complexation. Intended perspectives include the capabilities of predictive models to describe chemical equilibria in low temperature geochemical systems and the extent to which predictive models are constrained by direct observations. In context of the importance of pressure as a key variable controlling the pathways and fate of environmental chemicals, a need for further direct observations of chemical equilibria at high pressure, under conditions which are often challenging to the experimentalist, is evident.

Introduction : The term electrochemical stripping analysis is applied to a family of procedures involving a preconcentration of the determinand (or a salt or derivative of the determinand) onto the working electrode, prior to its direct or indirect determination by means of an electroanalytical technique 1,2 . Such a combination of an effective accumulation step with an advanced measurement procedure results in a very low detection limit, and makes stripping analysis one of the most important techniques in trace analysis. The original stripping analysis method involved the cathodic electrodeposition of amalgam-forming metals onto a hanging mercury drop (working) electrode, followed by the anodic voltammetric determination of the accumulated metal during a positive-going potential scan 3 . Numerous advances during the 1980s and 1990s, however, have led to the development of alternative preconcentration schemes and advanced measurement procedures that further enhance the scope and power of stripping analysis 4,5 . As a consequence, numerous variants of stripping analysis exist currently, differing in their method of accumulation and measurement. A recent text on stripping analysis is by Brainina and Neyman, 6 and recent reviews on adsorptive stripping voltammetry are by Kalvoda and Kopanica, 7 van den Berg, 8 and Paneli and Voulgaropoulos. 9 Problems in selecting an effective nomenclature for stripping analysis are discussed in this document. Stripping analysis incorporates a two step process - accumulation and determination - and the technique can be considered to be a 'hyphenated technique'. The method of determination has been included, usually, in naming a particular technique, but often the method of accumulation has not. In some cases, eg. adsorptive stripping voltammetry, the method of accumulation is given but no indication is given as to whether the determination is cathodic or anodic (or whether it measures a capacitance current due to desorption). The purpose of this document is to recommend classification, and relevant terminology, for the different procedures used in electrochemical stripping analysis.

Analytical chemistry of metal complexes with biomacromolecules based on the coupling of a high resolution separation technique with an element or species selective detection technique is critically discussed. The role of size-exclusion chromatography (SEC) with on-line atomic spectrometric detection is evaluated for the characterization of the metal distribution among the fractions of different molecular weight. Attention is given to the conditions for the separation of metallated biomacromolecular isoforms and sub-isoforms by anion-exchange and reversed-phase HPLC. Techniques for interfacing chromatography with atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectrometry (ICP AES) and ICP mass spectrometry (ICP MS) are assessed. The potential of electrospray (tandem) mass spectrometry for the on-line determination of the molecular mass of the eluting protein is highlighted. Perspectives for capillary zone electrophoresis (CZE), microbore and capillary HPLC with ICP MS and electrospray MS detection for probing metalloproteins are discussed. Applications of hyphenated techniques to the analysis of real-world samples are reviewed.