Proton-transfer reaction mass spectrometry

Proton-transfer reaction mass spectrometry (PTR-MS) is a technique developed almost exclusively for the detection of gaseous organic compounds in air. Volatile organic compounds (VOCs) in air have both natural and anthropogenic sources. Natural sources include the emission of organic gases by living objects, both plants and animals. A well-known example, which is discussed later in this review, is the emission of a variety of gaseous organic compounds in the breath of animals, which are released from both the digestive system and the lungs. Plants are major sources of organic gases, as is the decay of dead animal and plant matter. Subsequent photochemistry can add further compounds to the mixture. Consequently, even without contributions from humans, ambient air from the Earth’s atmosphere would consist of a complex mixture of VOCs.