Response of ammonium-selective microelectrodes based on the neutral carrier nonactin.

Ammonium-selective microelectrodes made with an ion-exchanger based on nonactin and having a tip diameter of 1 mum have been developed. The response of the electrode is linear from 10(-5) to 10(-1)M NH(+)(4) and the response time is 1 min. Applications of these electrodes can be found in biotechnology and microbial ecology, but the low selectivity with respect to K(+) and Na(+) limits their use to low salt environments. Concentration gradients in gels containing cross-linked urease were measured and found to be in accord with macrokinetic measurements.