One of the advantages of the electrochemically generated acid in our system is the absence of a conjugated base that could react and interf ere in the medium. In organic acidity we used the correspondence of the f aradaic currents with the proton concentration in the cell to calibrate the FAM fluorescence. Furthermore, we were able to calculate the pK a values of four diff erent acids in the presence of Bu 4 PF 6 , which are diff erent than the values reported in literature.