Studies on alkali and alkaline earth chromate by time-of-flight laser microprobe mass spectrometry and Fourier transform ion cyclotron resonance mass spectrometry.: Part I: differentiation of chromate compounds

Abstract

Alkali and alkaline earth chromate compounds have been examined by time-of-flight laser microprobe mass spectrometry (TOF-LMMS) and laser ablation Fourier transform ion cyclotron resonance mass spectrometry (LA-FTICRMS). The two ion detection modes show a strong correlation with the nature of the counter ion. Similar behavior is observed with first alkali chromate and second alkaline earth chromate. In the positive detection mode, the major cluster ion induced by alkali chromate laser ablation is the M 3CrO 4 + cation, whereas it refers to the two ion series (MO) n CrO + and (MO) n CrO 2 + with n = 1–3 in the case of alkaline earth compounds. In the negative detection mode, whereas laser ablation of alkali chromate systematically produced mixed metal anions, in the case of alkaline earth chromate, such anions appeared but in small quantity and only in specific cases. The comparison of the results shown by FTICR mass spectra and TOF-LMMS allows for a distinction between stable and less stable ionic species, with the relative intensity of the latter dramatically decreasing on the FTICR mass spectra. Moreover, the decrease of the counter ion in electronegativity (radius growth) leads to an exacerbation of the typical behavior of the compounds belonging to the two ranges. These two observations facilitate the understanding of ion formation processes. This aspect of the study will be presented in Part II following the present work.