Electrochemical method was used to study in elongational laminar and turbulent flows the mass transfer toward a rotating disk in different drag reducing solutions of two cationic surfactants (Arquad 16-29, Arquad S50) together with counter ions (Para-chloro benzoate, Nasal) by varying the concentrations of their mixture. The mass transfer in laminar flow conditions displays a first order transition characterized by a significant drop accompanied by strong instabilities and a hysteresis cycle at a critical angular velocity which depends on the counter ion to surfactant concentrations ratio zeta. The local wall shear stress in turbulent flow was measured using a microelectrode inserted flush with the cross-section of the rotating disk. The ratio influences the drag reduction onset: Arquad 16-29 was shown to be more efficient at lowest concentration values than the Arquad S50 for both the critical velocity transition in laminar flow and the onset of drag reduction in turbulent flow. (C) 2015 Elsevier B.V. All rights reserved.