Experimental estimation of the bisulfite isomer quotient as a function of temperature: Implications for sulfur isotope fractionations in aqueous sulfite solutions

Bisulfite (HSO3-) and sulfite (SO32-) compounds play key roles in numerous geochemical and biochemical processes extending from the atmosphere to the subseafloor biosphere. Despite decades of spectroscopic investigations, the molecular composition of HSO3-in solution remains uncertain and, thus, the role of bisulfite in (bio) chemical and isotope fractionation processes is unclear. We report new experimental estimates for the bisulfite isomer quotient (Q(i) = [(HO)SO2-]/[(HS)O-3(-)]; [] = concentration) as a function of temperature from the interpretation of Raman spectra collected from aqueous NaHSO3 solutions contained in fused silica capsules. In pure NaHSO3 solutions (1Na(+): 1HSO(3)(-), stoichiometric) over [NaHSO3] = 0.2-0.4 m (moles/kg H2O), the following relationship is obtained: