Figure 1

A simple quantitative criterion of buffering action.(See main text for detailed explanation) A, Communicating vessels model of partitioning processes. In a system of two communicating vessels (A and B), total fluid volume is the sum of the two partial volumes in A and B. In an equilibrated system, the partial volumes in the individual vessels can be described as functions of total fluid volume; these functions are termed "partitioning functions". The derivatives of the partitioning functions tell what fraction of a total volume change is conveyed to the respective vessel. B, Partitioning of a quantity in a two-compartment system. A given total change of quantity in the system produces two partial changes in compartments A and B. The greater the partial change in B, the smaller the change in A, and the greater the "buffering" of the quantity in A. C, Partitioning of H⁺ ions between water and buffer. Free H⁺ ions are added to an aqueous solution containing a weak acid (e.g. as strong acid). Some of the added H⁺ ions remains free, some become bound to buffer molecules. C, General definition of measures of buffering action. The differential dz/dy, paraphrased as d(buffered)/d(total), is termed the buffering coefficient b. The differential, paraphrased as d(buffered)/d(unbuffered), is termed the buffering ratio B.