Nature of the Other Substances Present in Solution

Indicators may participate in other chemical equilibria than those involving proton exchanges. When this is the case, their indicator property may be modified and even suppressed. For example, they can enter into complexation equilibria with proteins in biological media. This is the case with albumin. Based on this property, the reactive papers to detect it are quickly operant. 

The color-change interval depends on temperature since its pKa value, which is present in Henderson s relation, depends on it (as do all the equilibrium constants). 

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