Diffusate

Diffusate is the material that diffuses from a region of higher concentration to a region of lower concentration through a barrier or medium. In diffusion studies, diffusate refers to the portion of solute that has moved into the receiving phase across a membrane or boundary. The composition of the diffusate reflects the diffusing species, its concentration in the donor phase, and the extent of diffusion over time.

Determinants of diffusate formation include the concentration gradient, the diffusion coefficient of the solute in the surrounding medium, the available surface area of the barrier, and the barrier’s thickness and properties. Environmental factors such as temperature, pH, and the presence of other solutes can also influence the rate and extent of diffusion. The process is commonly described by Fick’s laws, which relate flux to the concentration gradient and the diffusion coefficient.

Contexts and usage vary by field. In laboratory diffusion experiments, the solute diffuses from a donor compartment into a receiving (diffusate-containing) compartment, and measurements of the diffusate in the receiving phase are used to characterize diffusion kinetics. In some clinical or older literature, diffusate may be used to refer broadly to substances that have diffused across a barrier; however, dialysate is the standard term for the dialysis fluid on the receiving side in dialysis applications. The term diffusate is thus most often encountered in diffusion-specific discussions rather than routine clinical practice.

See also: diffusion, permeation, dialysate.