Standard Solutions for UV-Spectrophotometry

Can one use a mixture of compounds when making a standard solution for UV-Spectrophotometry. For instance, one is attempting to find the casein concentration of milk using UV-spec and they have milk protein which has casein protein in, but not pure casein protein. Would it be feasible to make the standard solutions using the milk protein, knowing how much casein is in it, even if there are other proteins in there or if it is not pure casein?


