Günter Henrion

A technique to study the electrochemistry of minerals

Recently a new technique has been introduced to study the dectrochemistry of metals and alloys [1,2]. This socal led abrasive stripping voltammetry comprises a mechanical (abrasive) transfer of traces of the solid material onto the surface of a solid electrode and the following electrochemical oxidation or reduction of these traces with an appropriate measuring method (e.g., differential pulse voitammetry). It turned out that this technique is highly useful to study the electrochemistry of sparingly soluble salts, including a great variety of minerals. This method opens up new areas of research, not only because of the extreme fastness of measurements (including sample preparation) but also because of the superior quality of the voltammograms and the trace amounts of material (less than 1/tg) which are sufficient to perform the study. To know the electrochemistry of minerals is important for a deep understanding of the formation and transformation of minerals. It is not less important for a possible electrochemical metallurgy [3]. Last, but not at least, abrasive stripping voltammetry can develop toward an easy method for mineral identification [4] even in fieldwork. As an example the electrochemistry of the mineral boulangerite, PbsSb4SI1 (Neumtihle, Greiz, GDR) will be discussed here. This mineral belongs to the extensive group of sulfo-salt minerals [5]. Figure 1 depicts the differential pulse voltammograms obtained after abrasive transfer of trace amounts of the mineral onto the surface of a paraffine-impregnated graphite electrode. Curve A is the cathodic voltammogram with the reduction of boulangerite according to

Identification of solid materials with a new electrochemical technique — the abrasive stripping analysis

SummaryA new technique for the characterization of solid materials is proposed, consisting in the transfer of extremely small amounts of the solid substance by abrasion onto the surface of a suitable solid electrode. The abrased material is electrochemically stripped off and this process is traced with a voltammetric method, e.g., differential pulse voltammetry. The method allows the easy and fast identification of solid materials, avoids the dissolution of the sample and hence reveals information about the structure of the solid material, thus allowing electrochemical phase analysis. The proposed technique of abrasive stripping analysis is applicable to a wide range of inorganic and organic substances.

Abrasive stripping voltammetry — the electrochemical spectroscopy for solid state: application for mineral analysis

SummaryAbrasive stripping voltammetry possesses several features of a spectroscopy. It allows the qualitative and quantitative analysis of electroactive solid materials. This work is focussed on the application for the unambiguous identification of minerals (sulphides, sulfo-salt minerals, fahlores). μg-amounts of a mineral are sufficient to perform a series of measurements. Three different voltammetric modes were used to study the electrochemical behaviour of the minerals.

A reliable and ultrasensitive voltammetric method for the determination of molybdenum

SummaryThe determination of molybdenum(VI) in aquatic media by polarography, voltammetry and adsorptive stripping voltammetry using the formation of a Mo-chlorate-mandalic acid complex at +100 mV (SCE) is described. The 3 sblank-detection limit is 0.1 nmol/l with differential pulse adsorptive stripping voltammetry (DPAdsSV, catalytic current). The calibration graphs are linear up to 200 nmol/l for the latter, 400 nmol/l for staircase voltammetry without accumulation time and 1 mg/l for staircase polarography. The accuracy of the DPAdsSV method was checked by analysis of a standard reference water material. The utility of differential pulse voltammetry was tested in different aquatic media, e.g., tap water, ground water, surface water.

Multi-way principal components analysis of a complex data array resulting from physicochemical characterization of natural waters

Abstract Multi-way principal components analysis (MPCA) is an efficient tool for reducing higher dimensional data arrays. Using the Kroonenberg algorithm — which originally was developed for three-dimensional data arrays but may be generalized to arbitrary dimensions in a straightforward manner — MPCA is applied to a complex example from the chemistry of waters. The data originated from the measurements of fifteen physicochemical parameters (variables) at ten different locations (objects) within some specific area of the Niger delta. These measurements were consistently recorded 22 times (occasions) in the course of a year. MPCA allows the detection of spatial and temporal factors of influence and the classification of the parameters considered according to these factors.

Multivariate 3-way data analysis of amino acid patterns of lakes

Time dependent patterns of amino acid concentrations have been studied by HPLC for different lakes of the Berlin area. Data analysis has been performed by conventional principal component analysis as well as by its more recent N-way extension. It turns out that lakes mainly differ by their general amino acid production as a function of time and season. Apart from this, in a single case there occurs a specific pattern which might be related to an exterior influence. This pattern, although clearly detected, has been not stable over time. Measurements are reproducible with respect to time (comparison of two succeeding years) and to position (comparison of isolated parts of a lake).

A simple and convenient solid state microanalytical technique for identification and characterization of the high temperature superconductor YBa2Cu3O7−x

SummaryThe application of a new electroanalytical technique, abrasive stripping voltammetry, is described for the purpose of identification and characterization of orthorhombic YBa2Cu3O7−x. The method is based on the peculiar property of this compound that the copper ions therein cannot be reduced below the +1 oxidation state, whereas all other copper compounds exhibit this property. The total analysis takes about 2 min and is very reliable.

Multivariate correction of chemical interferences in hydride generation atomic absorption spectrometry

Abstract In hydride generation atomic absorption spectrometry, chemical interferences among hydride-forming elements lead to systematic errors in the determination of concentrations. Using the system of Se, Sb and As as an example of simultaneously occurring elements, it is shown how to remove the systematic underestimations by the use of multi-component calibration. The advantage of this approach relies on the multivariate treatment of mutual interferences. For the given problem, application of multiple linear regression turns out to be equivalent to partial least squares. Estimation of the standard error of prediction confirms the temporal stability of the model. Further, in contrast to the prediction of concentrations, an “inverse” model is established in order to attempt a description of interferences.

Parametric and bootstrap estimations of confidence intervals for representative sample weights

SummaryThe essential problem in representative sampling is a comparison of analytical and sampling errors. Application of analysis of variance (ANOVA) to this problem seems less appropriate than regression analysis based on Wilsons formula, because in the first approach the total analytical error is commonly underestimated. Furthermore, regression analysis allows derivation of confidence intervals for representative sample weights. In this context a parametric and a non-parametric procedure are described.

Differential staircase voltammetry - A new electroanalytical technique

SummaryA new voltammetric method is described, which uses a staircase ramp and measures the current during two small time intervals at the end of every potential step. The difference between these two currents is amplified and recorded. The obtained data suggest that the proposed method of differential staircase voltammetry is as sensitive as differential pulse voltammetry.