The Collaborative International Dictionary of English v.0.48:
Disinterestedly \Dis*in"ter*est*ed*ly\, adv. In a disinterested manner; without bias or prejudice. [1913 Webster]WordNet (r) 3.0 (2006):
disinterestedly adv 1: without bias; without selfish motives; "he decided the case disinterestedly"