Formation of tungstate‐containing cluster ions by polyoxotungstate anions under matrix‐assisted laser desorption/ionization conditions in the gas phase

Abstract

The gas-phase studies of transition-metal oxides continue to attract interest as such oxides are being used as catalysts in various oxidation processes. In this paper, singly negatively charged heteropolyoxotungstate and isopolyoxotungstate ion clusters were produced from Keggin-type polyoxotungstates by matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (MALDI-FTICR MS). It was found that the ion series [(PO(3))(WO(3))(n)](-), [(WO(3))(n)](-) and [(OH)(WO(3))(n)](-) were the main fragment ions in the mass spectra and the matrix greatly influenced the resulting cluster ion abundances. [(PO(3))(WO(3))(3)](-), [(WO(3))(3)](-) and [(OH)(WO(3))(4)](-) were the most intense ions in each series when 2-(4-hydroxyphenylazo)benzoic acid was the matrix, whereas [(PO(3))(WO(3))(4)](-), [(WO(3))(6)](-) and [(OH)(WO(3))(4)](-) were the most intense when dithranol (DIT) was the matrix. In addition, a new kind of hybrid ion [W(2)C(14)H(7)O(8)](-) was produced through the reaction of DIT and [(OH)(WO(3))](-) in the plume of the gas phase. These results highlight the utility of the MALDI-FT method for obtaining novel ion clusters and also show the stability of these clusters.

Extensive generation and characterization of ion clusters by silicopolyoxometalate anions under matrix‐assisted laser desorption/ionization conditions in the gas phase

“…In each ion series, the most abundant ions (magic numbers) were the [(HSiO 3 )(WO 3 ) 6 ] − , [(C 8 H 5 O m )(WO 3 ) 3 ] − , [(HO)(WO 3 ) 6 ] − , and [(W 7 O 21 ] −• cluster ions, respectively, which indicates their relatively more stable structures. We have previously reported that the DIT matrix can interact with tungstate anions to form an organic–inorganic hybrid [W 2 C 14 H 7 O 8 ] − ion cluster 19,20 . Likewise, it seems that the matrices DHAP and THAP can also interact with tungstate anions to generate a series of organic–inorganic hybrid tungsten‐containing ion clusters [(C 8 H 5 O m )(WO 3 ) n (H 2 O) x ] − in the gas phase.…”

TiO2 Nanocoral Structures as Versatile Substrates for Surface‐Assisted Laser Desorption/Ionization Mass Spectrometry

“…Figure a–b shows negative ion SALDI mass spectra of dodecatungstosilicic acid (H 4 SiW 12 O 40 , SiW12) and phosphomolybdic acid (H 3 PMo 12 O 40 , PMo12), which are typical POMs, obtained by using TNC substrates. By careful and detailed study, the SALDI‐MS signals were assigned as shown in Tables S1–2 …”

Formation of molybdate ion clusters by phosphomolybdic anions under matrix‐assisted laser desorption/ionization conditions in the gas phase

“…1, members . Unlike phospho-polyoxotungstate ion clusters [4] , molybdenum-tooxygen ratios are not in accordance with certain laws in phospho-polyoxomolybdate ion clusters when the numbers of molybdenum atoms are more than 6, such as [PMo 7 O 22 ] -, [PMo 14 O 42 ] -.…”

“…[1] Matrix-assisted laser desorption/ionization (MALDI) is an important mass spectrometric technique, [2] which has some inherent advantages, such as relatively low sample requirements, sensitivity and straightforward mixture analysis. Sometimes, some series of metal-related ion clusters can be efficiently produced by MALDI source [3][4][5] since the physical aspects of MALDI overlap with the laser ablation (LA) of molecular substrates to some extent [6] , particularly with the advent of delayed ion extraction and novel surface preparation protocolsdirectly dropping analytes from the solution on top of the pre-deposited matrix layer. In LA, two mechanisms could explain the formation of ionic species: [7] recombination and unimolecular dissociation before detection.…”