[TATP+NH4] + , was found at m/z 240. However, no ions at m/z 91 and 75 were found in a blank experiment involving the addition of methanol to the ion source. In our previous study, we also found the ammoniated TATP ion ([TATP+NH4] + , m/z 240) in the positive mode of operation using the ac/dc-APCI . This is due to the ammonia used in chemical laboratories for various purposes contaminating laboratory air. The adduct ion of TATP with ammonia, [TATP+NH4] + , m/z 240), is formed when ammonia is present in the laboratory air. The formation of the ([TATP+NH4] + , m/z 240) ion is facilitated by the presence of a sufficient amount of ammonia at high ion source pressures, such as 28 Torr. The adduct ion is formed by passing through its transition state complex, [TATP•••NH4] +* , and according to transition state theory, a third-body collusion is required to stabilize the intermediate transition state in order to obtain the product ion, [TATP+NH4] + , which can be ascribed by the equation :