传递的质子是从水合氢离子（H3O +）而来，对于质子亲和力比水大的物质和基团如乙醇、醚、羰基、羧基等都很容易进行质子传递；因为大多数被氧化的有机物，比如那些存在于气溶胶中的有机物都含有很多这样的基团，所以质子亲和力都比水大，在质子传递中用水合氢离子进行化学电离有望是一种高效并相对温和的使有机物电离的方式。

对应的英文解释是：

Proton-transfer-reaction (PTR) is one form of chemical ionization that has proven to be an effective technique for the measurement of many ambient VOCs . Proton transfer from hydronium ions (H3O+) is efficient for species with a proton affinity (PA) higher than that of H2O (691 kJ/mol), including molecules with alcohol, ether, carbonyl, carboxyl, nitrile, amine, or aromatic groups. Since most oxidized organic species, such as those expected to comprise much of the aerosol organic mass fraction, have a higher proton affinity thanwater, proton transfer chemical ionization using H3O+ is expected to be an effective, and relatively soft, form of ionization for these compounds.