An oxygen insensitive microsensor for nitrous oxide

A method to create an O2 insensitive and fast responding microsensor for N2O is presented. The elimination of O2 interference was obtained by attaching a capillary with an alkaline solution of ascorbate in front of the tip of an electrochemical microsensor that was sensitive to both O2 and N2O. A 0.1 mm layer of 2 M ascorbate at pH 12 was able to remove all O2 when measuring in air-saturated solutions (O2 partial pressure 21 kPa), and no reduction of N2O by the ascorbate was observed. The response of the sensor to N2O was linear from 0 to 1.2 mM, and the detection limit was less than 1 μM. The tip diameters of the sensors described in detail were 50–80 μm, but much smaller sensors can be constructed. The 90% response times were about 40–50 s. Interference of carbon dioxide was shown to be negligible with respect to environmental monitoring, and the sensitivity to acetylene, which is commonly used to inhibit nitrous oxide reductase in denitrification studies, could be kept sufficiently low for experimental work.