“…3,4 Conventional methods to determine stability constants fall into two categories, according to whether a separation step is involved or not. Direct determination methods, such as potentiometry, 3,5 polarography, [6][7][8] spectrophotometry, [9][10][11] etc., are regarded as standard methods, as no or little external interference is involved. On the other hand, two-step methods are usually more sensitive and selective, as they involve the combination of a separation technique, such as ultrafiltration, capillary iotachophoresis, ion-exchange chromatography, etc., 3,4,12 to a powerful detector.…”