- Abstract. The speciation of polysulfides in aqueous solutions was investigated by electrospray–ion trap and electrospray–time of flight mass spectrometry. The pH dependence of the observed total dissolved polysulfides' concentration followed the trend calculated based on reported thermodynamic constants. However, the observed species' distributions were substantially different from those calculated based on thermodynamic coefficients derived by UV spectroscopy. Notably, large abundances of heptasulfide, octasulfide and nonasulfide species were observed throughout the pH range 6 to 11. The large molecular weight anions had not been reported before in aqueous solutions although indirect evidence had suggested their existence.