 Using mercury dithizonate again as an example, one can shine light on the sample to turn the solution blue, then run a UV/Vis test every 10 seconds (variable) to see the levels of absorbed and reflected wavelengths change over time in accordance with the solution turning back to yellow from the excited blue energy state.From these measurements, the concentration of the two species can be calculated.The mercury dithizonate reaction from one conformation to another is first order and would have the integral first order rate law