Observations on the Use of Ion Spray Mass Spectroscopy for Elemental Speciation in Aqueous Solutions Without Recourse to Chromatography

Abstract

This paper describes preliminary experiments that are selected with the limited aim of assessing whether ion spray (IS) mass spectrometry, in its current state of development, is a viable technique for practical speciation without recourse to the use of chromatography. Further, it attempts to demonstrate that the ion spray interface, in contrast to electrospray ion generation, can handle, without modification, wholly aqueous media as well as mixed solvents and organic solvents. The instrumentation employed for this study was an unmodified, commercially available, triple quadrupole mass spectrometer. Thus, experiments are described which demonstrate the capability of IS to provide speciation information on, in this case, Ni in aqueous and methanolic media with and without the presence of the chelating ligand, EDTA. Additional experiments are reported for aluminium in combination with citric acid. The results confirm previous work and show that the source and interface conditions can be tailored to provide either molecular information or to reveal the presence of elements as their elemental ions. Aqueous solutions are handled successfully by the IS interface without modification and reveal the expected speciation patterns. However, several problems were encountered: the spectra, even for single component solutions, are complex and highly sensitive to operating conditions; new species can be generated in the ionisation–extraction process and conditions have to be tailored to ions of a particular polarity; elemental sensitivity is limited; and care has to be taken to avoid sample carry over. Given the complexity of the spectra, it is concluded that real samples will require prior separation by chromatographic or electrophoretic techniques and that MS–MS instrumentation is of considerable value for confirming the identification of individual species.

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