Intergranular segregation in a Fe-P-C model alloy after thermal ageing at 650 degrees C has been examined using Atom Probe Tomography (APT) and Auger Electron Spectroscopy (AES). The specimens were prepared using site-specific method combining focused ion beam (FIB) and Transmission Kikuchi Diffraction (TKD). Grain boundary's five macroscopic degrees of freedom (DOFs) were determined from the TKD map supplemented by 3D APT reconstruction. The phosphorus intergranular segregation values obtained using APT and AES techniques were in excellent agreement and equal to 1.6 +/- 0.7 at/nm(2) and 1.4 +/- 0.5 at/nm(2), respectively. The two techniques are complementary for a fully quantitative description.