N-4-Vinylbenzyl-N’-octadecyl-1,4-diazabicyclo[2.2.2]octane diammonium salt was synthesized and tested to determine its ability to selectively precipitate anions. Fifty-one common anions were tested. The reagent reacted most readily with the monovalent oxyanions of Groups VIIB and VIA, and the divalent oxyanions of Group VIB.