As shown in figure .b, the value of the split triple point, ∆pK c a , increases as the difference in concentrations increases. When this split occurs (i.e. for ∆pK a = ∆pK c a ), the buffer index of the solution presents a rather flat regime around pH = pK a2 , as can be seen in figure .c, but pH = pK a1 appears as a clear maximum of the buffer index. Below the critical value, the buffer index presents a single maximum and above that value, two maxima and a minimum are present, roughly and respectively for pH = pK a1 , i We chose that value of pKa for no particular reason as, in the considered situation, this curve is independent from this parameter. At this stage, we could have used reduced variables as proposed by Rilbe , however when we will consider the contribution of H 3 O + and OH -, it will not be possible to use such variables anymore so we prefer this homogeneous presentation of all equations studied here. ii A similar case can be made considering a solution of a weak diacid, in which case ∆pK c a = 1.204, see . pK a2 and pK a (the exact values of these extrema must be computed as a function of r and present a dependency similar to the ones presented in figure .a).