Aldehydes and ketones belong to a class of compounds called carbonyl compounds. The most common carbonyls in air include formaldehyde, acetaldehyde, and acetone. Carbonyls in air are collected by drawing air through a cartridge impregnated with acidified 2,4-dinitrophenylhydrazine (DNPH), which is very reactive toward carbonyls. The resulting products (hydrazones) in the cartridge are measured in the laboratory using high performance liquid chromatography to determine the levels of the carbonyl compounds originally present in air. Using DRI's standard carbonyl sampler with one channel, a cartridges can be exposed on a predetermined schedule