Electrospray mass (ESI-MS) spectrometric spectra were recorded on an Agilent LC/MS instrument in positive ion mode using a LC/QQQ 6420 series spectrometer equipped with an electrospray ionization source model G1948B. The instrument was used as simple ESI-MS equipment, thus the column was bypassed and 5 µL of the samples were introduced by flow injection analysis, with water as the solvent flow phase at a flow rate of 0.4 mL min−1. Preliminary experiments were performed to establish optimal experimental settings for the ESI-MS conditions, which were capillary voltage 4 kV, fragmentor voltage 135 V, and source temperature 300 °C. Nitrogen was used as the nebulization and desolvation gas at 15 psi and 11 L min−1. Spectra were obtained in MS2 scan mode with the Agilent software Masshunter B.06.00.
The mass spectra of L5, Zn2+, and their mixtures were investigated at I = 0.15 and 1.00 mol L−1 in NaCl(aq) and in the absence of ionic medium. Ligand and metal concentrations were 1.0·10−3 ≤ cL/mol L−1 ≤ 5.4·10−3 and 1.0·10−3 ≤ cZn2+/mol L−1 ≤ 5.0·10−3, respectively. The pH of each measurement solution was adjusted using NaOH standard solutions.
The mass spectra of L5, Zn2+, and their mixtures were investigated at I = 0.15 and 1.00 mol L−1 in NaCl(aq) and in the absence of ionic medium. Ligand and metal concentrations were 1.0·10−3 ≤ cL/mol L−1 ≤ 5.4·10−3 and 1.0·10−3 ≤ cZn2+/mol L−1 ≤ 5.0·10−3, respectively. The pH of each measurement solution was adjusted using NaOH standard solutions.