Helmut Offenbacher

Amperometric enzyme electrode

Abstract The theory of the steady state operation of an amperometric enzyme is derived. The reaction scheme includes diffusion of substrate and product through a membrane, the kinetics of the enzyme substrate reaction and the electrochemical regeneration of the enzyme. A simple diagnostic plot is derived which allows the rate limiting process to be identified, and the balance between the transport of substrate through the membrane and the enzyme and electrochemical kinetics to be determined. The effects of inhibition by the accumulation of product behind the membrane are also considered.

Fluorescence optical sensors for continuous determination of near-neutral pH values

Abstract The preparation and performance of two types of optical sensors for continous measurement of near-neutral pH values are described. the sensors are based on glass-immobilized fluorescent pH indicators and allow the determination of pHs in the range 6.4 to 7.7 with a precision of ±0.01 units. Response times are of the order of 1 min for 99% of the total signal change. Adverse effects of ionic strength are almost completely eliminated by appropriate treatment of the glass surface, thereby creating a well-defined and highly charged environment for the indicator. When the sensing layers are attached to the end of a bifurcated fibre optical light guide, a device for remotely sensing pH values is obtained.

Fluorescence sensor for monitoring ionic strength and physiological pH values

Abstract A sensor combination has been developed that measures both pH and ionic strength via two pH determinations. One of the two sensors has an immobilized pH indicator embedded in a micro-environment that makes its dissociation constant highly sensitive towards changes in the ionic strength of the solution. In the second sensor, the indicator is surrounded by charge ammonium groups, which renders the environment of the dye highly charged. Additional changes in ionic strength have practically no adverse effect. The difference in the pH values as displayed by the two sensors can be used to determine ionic strength together with pH in the near-neutral pH range.

A fast responding fluorescence sensor for oxygen

SummaryA sensor for the continuous measurement of oxygen partial pressure is described, which is based on the dynamic fluorescence quenching of covalently immobilized pyrenebutyric acid. Porous glass in combination with conventional glass is used as a solid support. The principal advantages of this sensor are a fast response time (less than 50 ms), a good spectral separation of excitation and emission maxima, and an acceptable long-term stability.ZusammenfassungEs wird ein Sensor zur kontinuierlichen Messung von Sauerstoffpartialdrücken beschrieben, welcher auf der dynamischen Fluoreszenzlöschung der kovalent immobilisierten Pyrenbuttersäure beruht. Poröses Glas in Kombination mit konventionellem Glas wird dabei als festes Trägermaterial verwendet. Die Hauptvorteile dieses Sensors sind eine schnelle Ansprechzeit (unter 50 ms), eine gute spektrale Trennung von Anregungs- und Emissionsmaximum, und eine akzeptabel gute Langzeitstabilität.

Preconcentration and semi-quantitative determination of aluminum(III) with immobilized morin

ZusammenfassungMorin wurde kovalent über eine Etherbindung und andere, weniger geeignete Methoden an Silicagel immobilisiert. Die resultierenden Konjugate sind in der Lage, Aluminium(III) sowohl durch Komplexierung an Morin als auch durch unspezifischen lonenaustausch an aktiven Stellen der Oberfläche zu binden. Werden diese Stellen aber silyliert, so erhält man ein Konjugat mit einer wahren Bindungskapazität von 0,5 mg Aluminium(III) pro Gramm Silicagel. Mit dessen Hilfe wird eine Vorkonzentrierung im ppm- und sub-ppm-Bereich möglich.Mit Morin-Silicagel gefüllte Teströhrchen wurden hergestellt, welche zur semi-quantitativen Bestimmung von Aluminium(III) geeignet sind, da zwischen der Konzentration der durchgeflossenen Meßlösung und der Länge der gebildeten fluorescierenden Zone eine Beziehung besteht.SummaryMorin was covalently immobilized onto silica gel via an ether link and other, less suitable methods. The resulting conjugates are able to bind aluminum(III) by both complexation by morin and unspecific cation exchange at active sites of the surface. When these sites are silylated, the conjugates exhibit a “true” binding capacity of 0.5 mg aluminum per gram, thus enabling the preconcentration of ppm and sub-ppm solutions of aluminum(III).Tubes filled with immobilized morin have been prepared, which are shown to be suitable for the semi-quantitative determination of the ion, as there is a relation between the aluminum concentration of the solution and the length of the fluorescent zone formed.