Abstract
Conductometric measurements are of interest in analytical chemistry. They provide an overall-sight of the ionic strength in electrolytes and can be used for analytical purposes if they are provided with a selectivity factor, e.g. enzyme membranes. Miniaturised transducers were formed by means of photolithography, thin film, and plasma technologies. Two- and 4-electrode measurements were taken to characterise sensitivity and dynamic range. However, using 4-electrode measurements expands the dynamic range from deionised water up to 1 mol KCl-solution and increases the sensitivity at high background conductivity. Such measurements were taken out with electrodes which had an interdigital distance of 50 μm and an area of 0.04 mm 2. Additionally, interdigital structures with interdigital distances of 5 μm were investigated. Coated with a poly-HEMA membrane wherein urease was immobilised, a urea sensor was constructed. The concentration-range of urea was 1–30 mmol urea in 20 mmol HEPES-buffer.
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