Abstract: In a surface desorption atmospheric pressure chemical ionization (DAPCI) source, positive reagent ions were produced by the corona discharge, ion/molecule reactions occurrebetween reagent ions and analytes. Adducts of RXD and reagent ions were analyzed by surface desorption atmospheric pressure chemical ionization-mass spectrometry (DAPCI-MS) under the optimized operation parameters of MS instrument. The results show that RDX forms covalently bound ionic clusters with formic acid and methylbenzene in DAPCI source.