Effect of instrumental ESI-MS parameters on aluminium(III)-ligand solution equilibria

Electrospray ionization mass spectrometry (ESI-MS) is being increasingly employed in the study of metal-ligand equilibria in aqueous solution [1, 2, 3]. In the present work, the ESI-MS spectral changes due to different settings of the following listed parameters are analysed: the solution flow rate (FS), the nebulizer gas flow rate (FG), the sprayer potential (E), and the temperature of the counter-current gas flow (T). 28 spectra were obtained for each of six samples containing aluminium(III) and 1,6 dimethyl 4 hydroxy 3 pyridincarboxylic acid at various pH, in the absence or in presence of a buffer, triethylamine, and acetic acid. The abundance of relevant ions were fitted versus the value s of FS, FG, E and T. Most of ionic intensities were significantly related to these instrumental parameters. Correlations were interpreted considering the presence of three kinds of perturbations occurring in the ESI ion source: formation of dimers in the droplets, different transfert efficiency from the gas phase for different complexes (according to their surface activity), and subsequent partial thermal decomposition of dimers and of some of the complexes in the gas phase. Our results show that the evaluation of the effects produced in the ESI-MS spectra by a change of instrumental parameters can allow to identify the perturbation occurring when metal-ligand solutions are studied by ESI-MS. References: [1] Valerio B. Di Marco et al., Mass Spectrometry Reviews, 2006; 25, 347-379. [2] Ray Colton et al., Mass Spectrometry Reviews, 1995; 14, 79-106. [3] Valerio B. Di Marco et al., Journal of Mass Spectrometry, 2009; 4, 120-127.