Portable system for near-real time measurement of gaseous formaldehyde by means of parallel scrubber stopped-flow absorptiometry

Formaldehyde, HCHO, is one of the important causal agents of sick-building syndrome. It is also an important product of ambient air photochemistry. We report here a portable instrument capable of a 0.08 ppbv limit of detection (LOD) and a time resolution of 5 min that is useful for both indoor and ambient air applications. The detection is based on efficient gas collection and chromogenic reaction with 3-methyl-2-benzothiazolone hydrazone (MBTH) through a pair of alternately sampling small-bore porous-membrane tube diffusion scrubbers (DS). The chemistry is well established, requires no special reagent preparation or elevated reaction temperatures and permits the use of inexpensive light emitting diode (LED)-based detectors without need for long path cells. Stopped flow alternate sampling allows an HCHO collection performance, an order of magnitude better than any previous system with high throughput and high sensitivity. Results for indoor and ambient air analyses are presented.