A concentration fraction indicates the particle size range over which the concentration has been calculated. For example, a concentration value reported as C[80-200] = 1.6 E07 particles/mL states that within the size range of 80-200 nm, there is a particle concentration of 1.6 E07 particles/mL.
When comparing data, it is critical to use a concentration fraction. This ensures that the concentration values being compared have been calculated over an identical size range.
When a concentration fraction isn't used, data comparisons are often misinterpreted and false conclusions can be drawn. Ideally, the minimum of the concentration fraction should not set far below the measured distribution maximum for a polydisperse sample.