The combination of isotopic distributions can be grouped into another matrix A of size, 𝑛 × 𝑝 where p is the number of chemical species considered. For the analysis performed in positive mode, all combinations of species of the constituents with no more than 5 time the same element are considered. For example, all species selected in a sample containing Ru, Pt, Pd, Ir, Rh can be express as 𝑅𝑢 𝑎 𝑃𝑡 𝑏 𝑃𝑑 𝑐 𝐼𝑟 𝑑 𝑅ℎ 𝑒 with the indices 𝑎, 𝑏, 𝑐, 𝑑, 𝑒 = 0,1,2,3,4,5 with 𝑎 + 𝑏 + 𝑐 + 𝑑 + 𝑒 ≥ 1.