Figure 1.

A, Prototype of the PTR-MS used in our studies. Air is pumped through a drift tube by a mechanical pump. H₃O⁺ ions are produced in a side arm by electron impact ionization of a He/H₂O mixture. Organic trace gases are ionized in the drift tube by proton transfer reaction with H₃O⁺, mass selected with a quadrupole mass detector and detected with a conversion dynode electron multiplier (CDEM). B, Schematic diagram of the gas inlet system for the PTR-MS used in analysis of Arabidopsis root VOCs. C, Prototype of the Erlenmeyer flask used to culture Arabidopsis roots and for the analysis of root-derived VOCs.