radical anions for use in the fragmentation of positively charged biopolymer ions by means of electron transfer are produced from substances previously unknown for use as etd production substances . the inventive substances produce radical anions that lead to electron transfer dissociations with a high yield of fragment ions . the substances have high volatility that allows them to be kept in unheated containers outside the vacuum system and transported into the vacuum system to an in vacuum electron attachment ion source via unheated lines and low molecular weights that allow the measurement of even very light fragment ions . in one embodiment , a suitable substance is 1 - 3 - 5 - 7 - cyclooctatetraene .