M. Hahn’s research while affiliated with Martin Luther University Halle-Wittenberg and other places

Die Wasseraufnahme getrockneter, insbesondere gefriergetrockneter Klärschlämme und ähnlicher Matrizes erfordert zur korrekten Einwaage für weitere Analysen die Bestimmung des Wassergehaltes der Trockenmasse. Aus den durchgeführten Untersuchungen ergab sich, daß infolge einer Vielzahl möglicher Reaktionspartner in Klärschlämmen und auch anderen Materialien eine direkte Bestimmung des Wassergehaltes mit Hilfe der Karl‐Fischer‐Titration nicht möglich ist. Die Bestimmung erfordert eine externe Extraktion entweder mit Hilfe eines zusätzlichen Extraktionsgases, realisiert z. B. im Gerät der Fa. Metrohm, oder mit Hilfe der Gasphase des Karl‐Fischer‐Reagenzes, realisiert im Gerät der Fa. ECH Elektrochemie Halle. Bei letzterer Variante kann auf eine separate Trocknung des Extraktionsgases verzichtet werden. Mit Hilfe eines Temperaturgradienten lassen sich die optimalen Ausheizbedingungen für die zu untersuchenden Materialien, z. B. Klärschlämme, ermitteln. Da in der Regel nur geringe Wassergehalte zu bestimmen sind, bietet die mikrocoulometrische Titrationsmethode Vorteile gegenüber der volumetrischen Bestimmung.

Electrochemical measurement methods are suitable for examining the hydrolysis and reactivity of chloramine T. The individual species can be separated by means of capillary electrophoresis. Voltammetrical methods make it possible to judge selectively on the oxidation efficiency of individual substances. By coupling the coulometric determination with sample preparation techniques, e.g., stripping out, volatile chlorine can also be determined. The stability of chloramine T solutions was tested at various pH values and hydrolysis reactions are described. It is shown that chloramine T differs from other active chlorine donors and hypochlorite/chlorine with regard to its reactivity.

The coupling is described of coulometric separation methods with an ion exchange separation step. Various methods of enrichment and separation are described using the analysis of nitrogen compounds, such as ammonia, urea and nitrite, as examples. A microcomputer controls the separation step and regulates the coulometric determination. Quantitative separations are achieved in all cases, so that the advantage of coulometric titration, as a precise absolute determination method, is retained.

Coulometric titration is employed in combination with a gas diffusion step for the quantitative separation and determination of volatile substances. Complete separation is brought about by filling the sample into a closed circulating loop and transporting it repeatedly past a microporous membrane. The combination of membrane separation module with the coulometric cell allows rapid separation and exploitation of the precise absolute determinations obtainable by the coulometric titration method. The high precision and selectivity of the determination and quantitative separation are discussed using ammonia and sulphur dioxide analyses as examples.

A device for AOX determination with high precision and reproducibility is described. It permits great sensitivity at low electrolyte volumes and high gas flow rates. After incineration, the halide ions are titrated against electrolytic silver(I). Computer-controlled square-wave polarization of the indicator electrodes allows extremely low noise titration curves. Control of the coulometric titration and incineration temperature by a personal computer enables the entire analysis to be automated. The device permits the determination of the AOX fraction in liquid samples, the elementary analysis of halogen in organic compounds, and the determination of AOX in air.

Coulometric titrations of ammonia and sulphur dioxide can be implemented with an improved selectivity in a measuring cell combining a batch type titration cell with a gas diffusion separator. The supporting electrolyte is propelled through the coulometric titration cell and the acceptor side of the membrane separator by means of a magnetic centrifugal pump. The sample solution flows through the donor side of the membrane separator. Acceptor and donor side are separated by a microporous PTFE-membrane. The measuring cell assembly allows both selectivity enhanced coulometric titrations with enrichment of the sample substance to be determined and the continuous coulometric detection of volatile species.