Competitive Potentiometric Study of a Series of 18-crown-6 with Some Alkali and Alkaline Earth Metal Ions in Methanol Using an Ag+/Ag Electrode

Tandem mass spectroscopy as a tool for investigation of complexes of PNP-lariat ether derivative with metal ions

The novel PNP-lariat ether L with cyclotriphosphazene ring incorporated in the macrocyclic structure was synthesized and checked by the electrospray mass spectrometry (ESI-MS) method for the ability to bind different types of ions Ag⁺ , Ca²⁺ , Cd²⁺ , Cu²⁺ , and Pb²⁺ . Furthermore, the stability constants of the abovementioned ion complexes with the investigated ligand have been determined by direct and competitive potentiometric methods. To evaluate the stability of various complex types and to confirm the way of metal cation binding, the tandem mass spectra of the investigated ligand and its complexes were taken. As a result, we obtained quite a good relationship between the number and main types of complex species observed in ESI-MS experiments and the forms of complexes for which the stabilization constants were determined by potentiometric methods. Moreover, we also concluded that in case of big discrepancies of stability constants, ESI-MS experiments could provide information about the most stable form of the complexes, but they fail when the differences between the strength of the coordination binding are slightly different.