The inductively-coupled plasma ion source for mass spectrometry is very sensitive for multielement analysis with detection limits down to sub part per trillion (ppt). Polyatomic ions which could be formed in the mass spectra may interfere in the analysis of some elements. Experimental conditions have great influences on the formation of polyatomic ions. The present work demonstrates that the skimmer materials (Au, Ag, Ni, Cu and Al) are participating in the formation of polyatomic ions. Heats of formation of polyatomic species formed from the skimmer materials such as: AuX, AgX, NiX, CuX and AlX, where X=Ar, O, N and H, are calculated by Gaussian program (G94W).