The principle is grasped when you consider an ammonia/ammonium buffer. pH and then hydrogen ion concentration is measured by glass electrode, and from the knowvn ratio between NH3 and NH4+ and the measured H+ you calculate the acidity constant of NH4+. If you add a metal ion like Cu2+ to the buffer the ammonia will bind partly to the metal ion and consequently the solution becomes more acidic. This you measure by glass electrode. The change in the ammonia concentration is easily obtained and knowing the total Cu2+ concentration you can calculate how many ammonia are bound per copper(II) ion. It is not at all necessary to use titration or Rossotti's equation. Make 10-20 solution with well determined amounts. Only if you need this as a research field do you need titration equipment and extended software for PC computations.