In this study, in order to investigate the mechanism of Li+ attachment process, dimethylarsinic acid (DMAA) was detected by selective-ion monitoring mode of ion attachment mass spectrometry (IAMS) and the Li+ binding energy of N-2, and DMAA was also calculated. The results indicated the possibility of the transfer of Li+ from N2Li+ to DMAA in IAMS analysis. This study could contribute to the development and application of IAMS technique.