We show that MALDI mass spectrometry, suitable for mixtures, is an indispensable tool in probing the mechanism of nanocluster synthesis enabling positive identification of nanoclusters. The size evolution of the mixture of larger clusters (Au-102, Au-68, Au-38) to form highly monodisperse Au-25 nanoclusters is demonstrated and probably includes the participation of Au(I) thiolate. The size evolution via structural reconstruction of the larger cores such as 38, similar to 44, 68, and 102 to a Au-25 nanocluster has been discussed.