Buffer Index and Buffer Capacity for a Simple Buffer Solution

Many papers that present the buffering effect of the simple buffer solution consider the notion of buffer index and buffer capacity as being equivalent. Moreover, IUPAC defies them as the same thing. According to the definition of the authors who have introduced these two units, the paper shows that there is a large difference between them. The buffer index can be defined as the differential ratio of the increase in the amount of strong acid or strong base added, to pH variation. The buffer capacity is numerically expressed to be equal with the minimum concentration of strong acid or strong base which causes the variation of buffer's pH with one unit. The field of application of both notions is different: the buffer capacity is used in the quantitative chemical analysis and the buffer index in studying biological systems.