文档介绍：and medicine, surface adsorption studies, gas detection, Lead
and the study of stochastic processes at various interfaces. Electrode
patibility of the ion-selective membranes and
Lead
semiconductor materials used in the construction of
CHEMFETs is the major practical problem standing in the
way of wide usage of these devices. By deliberate choice
both the electrochemical element (the membrane) and the
electronic preamplifier (FET chip) are exposed to a very Heater
hostile environment, the electrolyte solution. In such a Electrode
situation, the requirements that are placed on the encap-
sulation materials are much more stringent than those re- Sintered
Tubular ceramic
quired for ISEs. Once the encapsulation and membrane SnO2
former
attachment problems are solved, design of sensor packages
that will include data acquisition as well as data- Figure 3. Configuration of a semiconductor gas sensor. Source:
processing elements will be feasible (16). Refs. 23 and 24.
Using an operational amplifier, Perez-Olmos (19) im-
proved the sensitivity of ISE for measuring potassium and
calcium in wines. Knee and Srivastava (20) adapted an metallization deposited on the outer surface coated with
ISE to measure calcium in apple fruit tissue; calcium is a the sintered, but porous, tin oxide mix. In the work of Man-
critical mineral affecting postharvest handling and quality. denius and Mattiasson (22), ethanol, which is a reducing
A fully automated battery-puterized field- gas, was allowed to flow over the tin oxide coated surface
based ISE method for monitoring fluoride in water was of the sensor. The gas was absorbed onto the sensor surface
reported by Bond et al. (21). and produced a marked decrease in the surface electrical
resistance. By using a continuous dilution of the gas flow
Metal Oxide Gas Sensors streams, the lower limit of detection of ethanol was ex-
tended by their work to operate within the concentration
The most w