The separation of relatively small, fast-migrating anions by CE is not possible under standard conditions with cathodic EOF of relatively high velocity. Therefore, separation approaches for these analytes usually include suppression or reversal of the EOF using various cationic additives to the BGE or covalent coating of the capillary walls. In this study, novel phosphonium-based mono- and dicationic reagents (originally synthesized as ionic liquids) were evaluated as additives to the BGE for the separation of inorganic and small organic anions. The effects of these reagents on the EOF and their interactions with anionic analytes were compared. The effects of the additive's structure and concentration as well as the separation buffer pH have been studied. Propane-1,3-bis(tripropylphosphonium) fluoride proved to be the most effective additive, as it suppressed the EOF in the system and enabled remarkable manipulation of separation selectivity. A method for fast, reliable, and efficient separation of six inorganic and seven organic anions within 7 min time was developed using propane-1,3-bis(tripropylphosphonium) fluoride as an additive to the separation buffer.