What is the term for the concentration of a chemical in a pharmaceutical solution?

The term that specifically refers to the concentration of a chemical in a pharmaceutical solution is tonicity. Tonicity measures the osmotic pressure gradient of a solution compared to another solution, typically concerning cell membranes. It describes how the concentration of solutes in the solution influences the movement of water across a semi-permeable membrane, which is extremely relevant in pharmaceuticals where solutions are engineered for intravenous use or other applications.

Concentration refers broadly to the amount of a substance in a given volume of solution, but it does not capture the specific physiological effects of that concentration on cells and tissues. Viscosity pertains to the thickness or flow characteristics of a solution, which is important in determining how a drug can be delivered but does not relate directly to its chemical concentration. Purity indicates the absence of contaminants or impurities but again does not focus on the concentration aspect of the solution. Thus, tonicity is the term that best aligns with the concentration of a chemical as it pertains to its effects on biological systems.