It is possible to use the generalized and simple UV-Vis technique. We can use the Asmus method. It allows to simultaneously determine the stoichiometry of the metal-ligand interaction of a complex formation reaction, the value of the stability constant and the molar extinction coefficient. From this, the concentration of the complex can be known.
To know the mass, mass spectroscopies could help you. However, in very few cases, due to poor/no ionization, we may not give accurate result and in such a case you need to take XRD analysis which gives you the exact structure.