The gas flow subassembly consists of 8 silica-lined stainless steel tubes containing 3/4 Tenax-TA sorbent (0.5 gm) and 1/4 Carboxen 569 (by volume) separated by a plug of glass wool for sample adsorption. The tubes are connected at one end to a mechanical 8-position, zero-dead-volume valve for on/off switching between tubes. One of the tubes (tube 8, labeled "Park") is used as a parking position between sample collections. The tubes are connected at the other end to the electronic subassembly.
The electronic subassembly consists of a pulse pump used to pull air into the sampling device, a battery clip to hold the batteries in position, and four disposable C-sized dry-cell batteries to provide power. The small single-diaphragm pulse pump draws air at an adjustable rate (from 0.5 to 3.0 liters of air per 24-hours). A timer printed circuit board is used to deliver a timed power pulse to the motor. This allows allow air to be sampled slowly, so that sufficient time is allowed for atmospheric volatile organic compounds to be absorbed evenly throughout an adsorption tube, without saturation in any particular section.
The entire unit weighs approximately 2.3 kg. A recent modification to the inlet screen provides a 5-fold increase in the inlet area to minimize chances for obstruction of the inlet.