TNT produced a strong ion signal of the adduct ion, ([TNT+NO3-HNO2] -, m/z 242), when mixed with NG, PETN, and RDX at 28.0-30.0 Torr of air pressure using a modified HCD ion source with each explosive sample weighing 1 ng (Fig. ). Using the EIC for m/z 242, NG, PETN, and RDX also revealed their appropriate adduct ions with the NO3 -ion as minor ion signals (Fig. ). As a result, the modified HCD ion source can be used in combination with an MS system to detect explosives at trace to ultra-trace levels while employing air as a carrier gas. (c 1 )