The proportion of metal ions in a High Power Impulse Magnetron Sputtering discharge is a key information for the potential development of new materials and new layer architectures deposited by this technique. This paper aims to measure this proportion by using a homemade system consisting of a quartz crystal microbalance and a grid energy analyzer assembly. Such a system yields relevant results on the composition of the post-discharge depending on the nature of the gas (Ar, Kr, Xe) and the target materials (Pt, Pd, Au, Pt50Au50 and Pt5Pd95). In our conditions, the highest proportions of metal ions in the post-discharge are obtained by using Ar gas and reaches 10 %, 12 %, 50 %, 19 % and 88 % for respective Pt, Au, Pd, Pt50Au50 and Pt5Pd95 target, respectively.