Ion Spray Mass Spectrometry for Elemental Speciation in Aqueous Samples: Preliminary Investigation of Experimental Parameters, Matrix Effects and Metal–Ligand Complexation

Abstract

Ion spray mass spectra obtained from aqueous solutions are discussed. Ion clusters with large numbers of water molecules, very few water molecules or bare elemental ions could be obtained by adjusting the sampling orifice voltage, the skimmer voltage or the position of the ion spray nebulizer relative to the sampling orifice. In some cases submillimeter changes in the position of the ion spray nebulizer can dramatically affect the nature of the spectra observed. There is evidence of declustering between the skimmer and first ion lens as well as between the sampling orifice and skimmer. Interpretation of the mass spectra must be carried out with care as potential spectral overlaps are common. Use of a triple quadrupole mass spectrometer allows assessment of potential spectral overlaps. Ni–EDTA complexation was investigated. The Ni ⁺ signal correlated with the expected concentration of free metal ions in the solution not the total metal concentration even when relatively harsh conditions that produced bare metal ion spectra were used. Matrix effects due to high concentrations of NaCl and HCl were briefly investigated.