Quantization of ion microprobe mass spectrometric analyses has been complicated by the variation in the ion yield of an element contained in different matrices. This work demonstrates that, for O−and Cs+bombardment, these ion‐yield variations are solely attributable to variations in the matrix sputtering yield. It is argued that the matrix sputtering yield determines the near‐surface concentration of the ion‐yield‐enhancing species O and Cs.