Negative-ion low-temperature fast-atom bombardment mass spectrometry of monomeric and dimeric [60]fullerene compounds

Abstract

Negative-ion low-temperature fast-atom bombardment mass spectrometry (LT-FAB-MS) is applied to. Only in the case of the dimeric C 120 O has the use of atmospheric-pressure chemical ionization (APCI) and electrospray ionization (ESI) been reported. 7 Thus, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) represents the only mass spectrometric technique for most of the dimers so far. 4,[8][9][10][11][12][13] However, MALDI-TOFMS exhibits limitations in the case of the rather unstable C 120 5,6 and it does not provide the unambigous identification of C 120 OS 13 because this cannot be distinguished from C 120 O 3 under these conditions.Good solubility of the sample in the matrix is a prerequisite for FAB-MS. [17][18][19][20] Consequently, the problems with FAB-MS arise from the extremely low solubility of the [60]fullerene dimers in conventional FAB matrices. Recently, a technique was introduced which employs volatile solvents, e.g. methanol, dichloromethane and toluene, as matrix in FAB-MS. 21 This is achieved by cooling the solvent/analyte mixture with liquid nitrogen and performing the measurement under low-temperature (LT) conditions. As a result, a solvent ideally suited for the analyte can be chosen regardless of its volatility. Independently, Shiea et al. published an alternative approach to the use of LT liquid secondary ion mass spectrometry. Using their method, they obtained mass spectra of the phosphaoxetane-type intermediate of the Wittig reaction. 22The aim of this paper is to outline the application of negative-ion LT-FAB-MS to the title compounds in both low-resolution (LR) and high-resolution (HR) mode. EXPERIMENTALA JEOL JMS-700 sector instrument (JEOL, Tokyo, Japan) was used for LT-FAB-MS. The FAB gun was operated with Xe at an emission current of 8 mA and at an accelerating voltage of 6 kV. On the stainless steel FAB probe tip the solid [60]fullerene compounds were dissolved in 2-3 mL of a 10 : 1 mixture of 1-chloronaphthalene (Cl-naph) and 3-nitrobenzyl alcohol (3-NBA). The sample was subsequently frozen by immersion into liquid nitrogen for 15 s 21,23 and then immediately transferred into the vacuum lock to keep condensation of atmospheric water to its surface low. Spectra were monitored during thawing of the sample in the ion source which was kept at 40°C. Final spectra were obtained by averaging 3-7 scans. For low-resolution measurements (R = 2000) the magnet was scanned over the mass range of interest, i.e. m/z 100-1000 for the monomers, m/z 600-1800 for the dimers, in about 12 s per cycle. For high-resolution measurements (R = 5000), scans of the accelerating voltage were used to cover the narrow range necessary to include two reference peaks. Internal calibration of the mass scale was achieved using [(H 2 SO 4 ) n HSO 4 ] À cluster ions generated from concentrated sulfuric acid which was applied to the position opposite to the analyte on a dual-target FAB probe.C 60 was purchased from Hoechst (Hoechst, Germany). Characterization of C 120 OS was part...

Reversible Dimerization of [5,6]-C60O

“…14 This species was found to have C 2V symmetry and two furanoid bridges linking the fullerene cages; it has since been the subject of various experimental and theoretical investigations. 6,13,[15][16][17][18][19][20][21][22][23] 24 A recent study in this laboratory uncovered a new isomer of C 60 O, the [5,6]-open oxidoannulene (oxa-homo[60]fullerene), which can be simply produced through photolysis of the ozonide C 60 O 3 . Following up on a preliminary report, 25 we describe here a dimerization reaction of this [5,6]-C 60 O species that proceeds in room-temperature solution to form a new isomer of C 120 O 2 .…”

Analysis of three different types of fullerene derivatives by laser desorption/ionization time‐of‐flight mass spectrometry with new matrices

“…However, most fullerene derivatives are thermally labile solids of low vapor pressure, and readily release the ligands to regenerate the fullerene core when heated, so most traditional ionization methods are often inapplicable in view of the difficulties in transferring the neutral molecule into the gas phase without inducing dissociation. In order to achieve ‘soft’ evaporation and ionization of fullerene derivatives, those ionization methods which can avoid harsh heating, including field desorption,4 low‐temperature fast‐atom bombardment (FAB),5 desorption chemical/electron ionization (DCI/DEI),6 electrospray ionization (ESI),7 nanospray ionization,8 laser desorption electron attachment time‐of‐flight (LD‐EA‐TOF),9 laser desorption/ionization time‐of‐flight (LDI‐TOF),10 and liquid secondary ionization (LSI),11 have been applied. Though these methods can achieve partial success, considerable fragmentation of the thermally unstable fullerene derivatives is still observed as a result of the high internal energies produced in the molecules during the evaporation/ionization process.…”

Low‐temperature SIMS mass spectra of diethyl ether

“…Low temperatures (LT) in sample handling for fast atom bombardment (FAB) and secondary ion mass spectrometry (SIMS) measurements have allowed secondary emission mass spectra of many volatile organic compounds to be obtained 1–22. LT FAB data have also been employed in the elaboration of basic models of FAB mechanisms, since they provided information about processes occurring in a wide temperature range.…”