Analysis and physical significancy of the kinetic parameters associated with albumin adsorption onto glassy carbon obtained by electrochemical impedance measurements

The kinetics of albumin adsorption onto a glassy carbon rotating disk electrode in a phosphate buffer, is reported from the time variations of the double-layer capacitance C_d, of the charge transfer resistance R_t and of the Tafel coefficient of the electrochemical reaction b; these three electrical quantities are determined by electrochemical impedance and faradaic current I measurements. The variations of C_d, 1/R_t, b  (R_tI)^?1 and I can be written under the form: α₀ + α₁ e^?t/τ1 + α₂ e^?t/τ2, where α₀, α₁, α₂, τ₁, τ₂ characterize a given electrical quantity. We demonstrate that this type of variation validates a two-step adsorption mechanism already proposed, starting from simply taking into account C_d(t). We analyze and discuss comprehensively various possibilities of interpreting the shifts between the time-constants associated with thevarious quantities as well as the correlations between these constants and those associated with physical adsorption phenomena.