ABSTRACT

Tonicity is an important factor in the formulation of products intended for application to sensitive mucous membranes of organs such as eye, ear, and nose. This chapter introduces tonicity with respect to its physiological significance and discusses the physicochemical basis for tonicity and colligative properties. It provides a brief review of methods of measuring and/or calculating tonicity and illustrates the established methods of adjusting tonicity and the examples of each of the methods. The most direct method for measurement of tonicity obviously would be to observe changes in erythrocytes on mixing solution with blood. From the theoretical background presented, one can easily devise his or her own methods to adjust tonicity of solutions using the principles of colligative properties. The issue of tonicity needs to be addressed from this perspective because organic solvents and the surfactants behave differently in solution than do the traditional solutes whose characteristics in solution are well-understood.