Adsorption and desorption at a surface are frequently the physical-chemical basis for boundary conditions used in analyzing bulk transport. The common Langmuir-like specifications of adsorption and desorption fail to match observations if desorption does not occur, involves more than one adsorbed state for one or more molecular types, or depends strongly upon the presence of particular dissolved species. In this paper the Langmuirian formulation is generalized to account for such phenomena. The result is fitted to data of Brash that quantify the Vroman effect, manifested as sequential adsorption of proteins from diluted blood plasma. The fitted parameters are then used to quantify ringlike patterns of protein adsorption that have been observed when dilute plasma is injected into the narrow space between a glass slide and a spherical lens resting on it. Previous elaborations of the Langmuirian boundary condition either fail to account for important qualitative features of complicated adsorption, or treat it with highly particular and not widely accepted parameters.