The effect of various parameters on the grafting of pyridine, by electrochemical reduction of 3-diazopyridinium cations generated in-situ, on a glassy carbon electrode was investigated. More specifically, the influence of 3-aminopyridine and NaNO2 concentration used for the diazotization reaction and the influence of the grafting conditions such as time and potential used for reduction of the diazonium cations, were investigated by cyclic voltammetry, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. The presence of immobilized pyridine at the electrode surface was demonstrated by X-ray photoelectron spectroscopy measurements and indirectly, by the blocking effect of the grafted layer. The best blocking effect is obtained for a diazotization reaction of 1 min. and 1 equivalent of sodium nitrite. As a general observation, when the time is increased and the reduction potential is made more negative, the higher blocking effect that is observed indicates a more compact layer and a higher surface coverage of the glassy carbon electrode. The apparent pKa of the immobilized pyridine was determined by cyclic voltammetry in the presence of Fe(CN)(6)(3-/4-) solution of different pHs and found to be equal to 5, which is close to the pK(a) value (5.25) of pyridine in homogeneous solution. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.054209jes] All rights reserved.