A new approach to determine the ratio of redox active species such as SeIV/SeVI and AsIII/AsV in marine systems

► Relative hydrogen score gives an information on the redox capacity of the marine system. ► rH can be used instead of Eh in this study. ► Ions in solution interact with each other as well as with water molecules. ► Electrostatic activity coefficient can be used instead of activity coefficient. ► We are suggesting a new Nernst equation. The ratio of redox active species contributes to the researches about marine systems in many ways. Are marine systems reductant or oxidant? For this purpose, redox active species are analyzed by using high technology instrumental analyzers such as AAS, ICP, and HPLC. Then, all ion pair species are compared to each by calculating their ratios. These technologies are very expensive, and it takes long time to obtain the results. In this study, we suggested a basic method by using pH and Eh. Therefore, the Nernst equation expression was rearranged by using relative hydrogen (rH) and electrostatic activity coefficient (Fel). Additionally, the ratio of the redox active ion pair species SeIV/SeVI and AsIII/AsV was calculated.