Where Q is the quencher concentration (mmol L^-1), I_f is the fluorescence intensity, I_abs is the intensity of absorption of the incident radiation, and k_f and k_q are the reaction rate constants.

To calculate k_q / k_f enter data pairs (Q, I_abs / I_f), and then click the Plot tab. To see the value of k_q / k_f (slope) click the Least-Squares Analysis tab. To pick off a value on the graph, move your cursor to the desired location then click and hold.