Quantitative Analysis of Urea in aq. solution
In clinical chemistry, urea is quantitativly determined as follows:


Hydrolyze urea with urease to ammonia and carbon dioxide
react the ammonia with 2-oxo-glutarate in the presence of glutamate dehydrogenase and $\ce{NADH}$: $\ce{NADH}$ is converted to $\ce{NAD+}$
monitor the decay of the UV absorption of $\ce{NADH}$ at $\lambda$= 340 and 410 nm