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A potentiometric test strip has been developed. It consists of an indicator electrode and a reference electrode. Both electrodes are prepared on filter paper as a microfibre matrix, encapsulated by the use of heat-sealing film and separated by an insulating plastic film or held at a distance during measurement. The reference electrode is a redox electrode. For the preparation of the ion-selective electrode a standard ion-selective PVC-matrix membrane cocktail is deposited in the microfibre matrix. Potassium- and sodium-sensitive test strips have been prepared and characterized. The electrochemical response of the potentiometric test strips is close to that of macro ion-sensitive electrodes using the same ion-selective membrane material. It should be possible to produce the test strips by mass-production technologies. So in future they may offer a new possibility for a more precise low-cost on-site determination of ions.

The construction of double matrix membranes (DMM) for disposable NH4+, Na+ and pH sensors is described. The usual polymer matrix membrane was incorporated in an inert micro fibre matrix (MFM). Capillary forces distribute the cocktail homogeneously in the MFM; this also determines the thickness. Sensors using the new DMM have shown selectivity, detection limits and slope comparable with polymer matrix membranes. The advantages of DMMs are their mechanical stability, the feasibility of low cost mass production with identical parameters and improved handling.

A potentiometric urea-sensitive biosensor using a NH + 4 -sensitive disposable electrode in double matrix membrane (DMM) technology as transducer is described. The ion-sensitive polymer matrix membrane was formed in the presence of an additional electrochemical inert filter paper matrix to improve the reproducibility in sensor production. The electrodes were prepared from one-side silver-coated filter paper, which is encapsulated for insulation by a heat-sealing film. A defined volume of the NH + 4 -sensitive polymer matrix membrane cocktail was deposited on this filter paper. To obtain the urea-biosensor a layer of urease was cast onto the ion-sensitive membrane. Poly (carbamoylsulfonate) hydrogel, produced from a hydrophilic polyurethane prepolymer blocked with bisulfite, served as immobilisation material. The disposable urea-sensitive electrode was combined with a disposable Ag/AgCl reference electrode to obtain the disposable urea biosensor. The sensor responded rapidly and in a stable manner to changes in urea concentrations between 7.2×10 −5 and 2.1×10 −2 mol/l. The detection limit was 2×10 −5 mol/l urea and the slope in the linear range 52 mV/decade. By taking into consideration the influence of the interfering K + - and Na + - ions the sensor can be used for the determination of urea in human blood and serum samples (diluted or undiluted). A good correlation was found with the data obtained by the spectrophotometric routine method.

In this paper we describe a disposable sodium sensor in double matrix membrane technology. This sensor is prepared from filter paper with an evaporated silver conducting line on one side. For insulation the sensor is laminated with a pre-perforated heat-sealing film. A defined volume of an ion-sensitive polymer matrix membrane cocktail is filled into one hole. So an ion-sensitive coated film sensor in double matrix membrane technology is produced. The double matrix membrane is formed by the polymer matrix membrane and by the additional filter paper matrix. The response behaviour of the sodium electrode is comparable with conventional macro ion-selective electrodes. By this technology a mass production of low cost sensors is possible.