Abstract: A system and method for ascertaining the concentration of a preselected target substance, characterized by a mitigated tendency for yielding results distorted by a departure from a state of calibration, i.e., by “drift”, which drift is ordinarily caused by temperature and humidity variations; drift-mitigation is achieved by exposure of a target substance to a metal oxide semiconductor material, the temperature of a heating element operatively associated with said material being cycled between a low-temperature interval and a high-temperature interval, in which latter interval the material's temperature is raised to a level at or above the minimum temperature for rapid formation of one or more oxides of the target substance, the oxide formation taking place in a sufficiently short time that the conductivity is reflective of a transient signal amplitude in a brief interval of time, such that the external factors causing drift do not have sufficient opportunity to distort the concentration determination.