A collision/reaction cell ICP-MS was used to develop a method for the multi-element determination of Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Nb, Mo, Ag, Cd, Sb, Cs, Ba, Hg and Pb in mastic gum. Evaluation of helium and hydrogen as cell gases took place and their ability to reduce several types of interference arising from a Si, S, P, C, Cl and F based matrix was investigated. Likewise, much polyatomic interference was attenuated efficiently by the effect of kinetic energy discrimination. Moreover, a study of stopping curve measurements was performed. Thus, measurements of the ion loss caused by collisions, reaction cross-sections given by the Langevin–Gioumousis–Stevenson model and collision cross-sections were carried out. The method was validated and the calculated recoveries for all elements (at three concentration levels) were ranged between 92.6% (Ti) and 105% (Ag) and the relative standard deviation (%RSD) of reproducibility was ranged between 1.6% (Co) and 9.9% (Ca). The limits of detection ranged between 0.11 ng g⁻¹ (Cs) and 1.12 μg g⁻¹ (Ca). The trueness of the method was also checked by the analysis of a standard reference material (SRM, 1573a tomato leaves).