3.3. Electrospray-Ionization Mass Spectrometry (ESI-MS) Measurements

Mass spectrometric data were obtained by means of a Varian 500-MS LC hexapole ion-trap mass spectrometer (Palo Alto, CA, USA). The experiments were performed in positive and negative ion-mode for AlaSal as well as the Co(II)–AlaSal system in 50/50% (v/v) methanol/water mixture, providing a more stable spray than water alone [65]. A background electrolyte was not added. The concentration of the ligand alone in the solution was 10⁻² M, while the AlaSal concentration in the Co(II)–ligand system was 2 × 10⁻² M at the molar ligand–metal ratio equal to 2:1. The samples were brought to various pH values known to achieve maximum concentrations of particular complexes and ionic forms of the ligand; these values were based on potentiometric species distribution graphs. All samples were introduced into the ESI-MS source by continuous infusion using an instrument syringe pump at a rate of 10 μL min⁻¹. The ESI-source was operated at 5.00 kV and the capillary heater was set to 350 °C. The cone voltage was within the range 40–120 V.