Studies of the chromium oxygenated cluster ions produced during the laser ablation of chromium oxides by laser ablation/ionization Fourier transform ion cyclotron resonance mass spectrometry

Abstract

Trivalent and hexavalent chromium oxides have been examined by time-of-flight laser microprobe mass spectrometry and Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). The positive-ion spectra show a strong correlation with the valency of chromium in the oxide. Thus, the positive cluster ion distribution and the presence of characteristic chromium cluster ions allow us to distinguish the two oxides. Metallic compounds present in industrial environments have been widely studied over the last ten years because of their toxicity. Among them are the chromium compounds, the toxicity of which depends on the metal oxidation state. Indeed, while chromium III is essential as a trace element for the normal functioning of living organisms (50-200 µg is necessary per day), chromium IV is known to have toxic effects on biological systems.1 In particular, it can cause DNA damage, cancer or allergic reactions. Thus, the valency determination of chromium is of first importance from a health point of view and many techniques are utilized for the determination of the stochiometry of chromium compounds. The most commonly used are UV/visible spectroscopy, 3-5 atomic absorption spectroscopy, 6 electrochemical techniques, 7,8 electrophoretic techniques 9 and ion chromatographic analysis.10 However, all these techniques use liquid samples, and oxidation or reduction reactions can occur during the dissolving of the chromium compounds.To overcome this problem, 'in situ' techniques such as Raman spectroscopy 11,12 or X-ray absorption spectroscopy 13 have been used; they require solid samples and thus give results more representative of the valency of the chromium in the original sample. Mass spectrometry coupled with the laser ablation/ionization process is another 'in situ' technique. Poitevin et al. and Hachimi et al. 14,15 have previously established a methodology to discriminate between trivalent and hexavalent chromium compounds by studying the relative intensities of negative cluster ions. Our purpose was to transpose this methodology to the study of positive cluster ions by time-of-flight laser microbe mass spectrometry (TOF-LMMS). In addition, we used the Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) technique with the aim of obtaining a similar discrimination of both oxides and getting a better understanding of the precursor ions, in particular the CrO + ion, present before the occurrence of clusters. EXPERIMENTAL SETUPTime-of-flight laser microprobe mass spectrometry TOF-LMMS experiments were performed using a LAMMA 500 instrument (Leybold-Heraeus, Germany) in a transmission arrangement. In our modified system 16,17 the second harmonic of a Nd-YAG laser (532 nm) pumps a dye laser (TDL50 D of Quantel, France) which is used for the ionization step. Harmonic frequencies of the dye laser are selected by a holographic network and can be doubled by a doubling crystal cell (DCC). The various wavelengths are separated by a quartz separation prism by adjusting its orientation. The alignment of...

Evidence of chromium-cobalt binary cluster formation by pulsed laser evaporation

“…This ion was previously described in work by Aubriet et al 29 The next observed set, dichromium oxide clusters Cr 2 O + at 120 amu and Cr 2 O 2 + at 136 amu were also calculations indicate that all of the observed intermetallic clusters are thermodynamically favorable, therefore, their presence in the mass spectrometer is an rational result. Given the high temperatures in the laser ablation process, the relative magnitudes of the exoergicity are not expected to be manifested in the ratio of peak heights.…”

Cerium Oxyhydroxide Clusters: Formation, Structure, and Reactivity

“…In the projectile category, Gianotto and Groenewold investigated a variety of aluminum, silicon, and chromium oxides, generating small-to-medium sized cluster ions with rhenium tetroxide (ReO 4 -) as the projectile. 46-53 Laser ablation is more commonly used, and Aubriet [54][55][56][57][58] and Gaumet [59][60][61][62][63] have used it for forming alumina, silica, and d-block oxyanions. Laser irradiation has also enjoyed extensive use for forming metal oxide clusters by targeting the laser on a rotating metal rod as pioneered by several groups, [64][65][66][67][68][69][70][71] enabling study of a wide variety of transition metal oxides; this approach tends to form hypo-oxidized species, and the extent of oxidation can be manipulated by seeding the ablation region with oxygen.…”

UV laser ablation of GdCa4O(BO3)3 (GdCOB) investigated by Fourier transform ion cyclotron resonance mass spectrometry

“…In that case molecular oxygen as well as metallic cation could be in their ground or excited states. 15 The two former processes of MO þ ion formation have been already suggested for transition metals 15,27 and for lanthanide compounds. 28 Moreover, Willson et al 28 have proposed another way of MO þ formation-chemiionization-when lanthanides are ablated in oxygen reactive atmosphere.…”

“…Note that most of the experiments are performed with the total or partial ejection of the major ion (Ca þ , BO 2 À ) in order to enhance the detection of the signal delivered by mixed oxygenated cluster ions. 15 The (partial or total) ejection of abundant ions in our experimental procedure allows the abundance of large cluster ions to be increased without any loss of information. Indeed, ejection of a high concentration of a single type of ion from the ICR cell often enhances signal because of reduced Coulomb ejection of other ions.…”