Since proteins absorb light at a specific wavelength, a spectrophotometer can be used to directly measure the concentration of a purified protein in solution. It is important to note that direct UV measurement at 280 nm yields highly reproducible measurements since no reagents are added to the protein solution and the protein of interest was not modified or inactivated during the process. It also produces quick results since the sample does not need to be incubated in order to complete the process.