AbstractThe effect of halides and different buffer anions on the quenching of the fluorescence of the new probe 10,10′‐bis(3‐sulfopropyl)‐9,9′‐biacridine (SPBA) has been studied using fluorescence and decay time measurements. The linearity of the Stern‐Volmer plot indicates that fluorescence quenching by halides can be described reasonably well by a single‐exponential decay with a K of 4.06 times 106M‐1s‐1for chloride, 7.83 times 106M‐1s‐1for bromide and 1.12 times 107M‐1s‐1for iodide. We have found that SPBA is collisionally quenched also by the buffers 3‐(N‐mor‐pholino)propanesulfonic acid (MOPS) and N‐2‐hydroxy‐ethylpiperazine‐N′‐ethansulfonic acid (HEPES). The bi‐molecular rate constants are 1.67 × 106M‐ls‐1for HEPES and 1.44 times 106M‐1s‐1for MOPS.