In studying grain boundary segregation in Cu–Bi alloys by means of Auger electron spectroscopy samples must be broken in-situ. Consequently, the distribution of segregants on both sides of fracture path must be considered quantitatively. This question can be addressed by studying the influence of an adsorbed oxygen layer on the intensity of Auger peaks. This oxygen layer forms on the fracture surface when it is intentionally exposed to air. In this work, the values of Bi coverage have been measured both on the as-fractured Cu fracture surface and on the fracture exposed to air. The coverage values evaluated from the model of a crosstie-like pattern agree better with each other than those from the model of a continuous layer. Our study reveals that the Cu-Bi bond is weaker than the Bi-Bi bond.