There are colorimetric methods for both that a search will quickly reveal

No, you cannot use US-VIS for measure Urea and ammonia in the urine.It may be long or costly process. There is an extremely huge list of all the factors that are a part of your rank. UV-Vis is a general procedure since in the UV-visible wavelength spectrum, most molecules absorb light. The UV frequency is between 100 and 400 nm, and the visible spectrum is between 400 and 700 nm. However it can be used for blood sample.most molecules absorb light. The UV frequency is between 100 and 400 nm, and the visible spectrum is between 400 and 700 nm.