A chemical-sensing apparatus is formed from the combination of a chemical preconcentrator
which sorbs and concentrates particular volatile organic chemicals (VOCs) and one
or more chemiresistors that sense the VOCs after the preconcentrator has been triggered
to release them in concentrated form. Use of the preconcentrator and chemiresistor(s)
in combination allows the VOCs to be detected at lower concentration than would
be possible using the chemiresistor(s) alone and further allows measurements to
be made in a variety of fluids, including liquids (e.g. groundwater). Additionally,
the apparatus provides a new mode of operation for sensing VOCs based on the measurement
of decay time constants, and a method for background correction to improve measurement precision.
