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Time-of-flight mass spectrometry of mineral volatilization: Toward direct composition analysis of shocked mineral vapor
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Image of FIG. 1.
FIG. 1.

Schematic of the impact vaporization mass spectrometer. Top: a high-velocity projectile strikes a driver plate, onto which is mounted a thin, polished mineral sample. The resulting shock wave releases neutral and ionic species from the mineral. In laser calibration experiments, ionization is realized by focusing a pulsed nitrogen laser onto the mineral. Neutrals released from the mineral are ionized by the electron beam, and the resulting ions are collimated, then pulsed into a time-of-flight mass spectrometer. Ions created at the mineral surface are similarly analyzed, but without the additional electron-ionization step. Ions can be excluded from analysis of neutrals using a repelling grid near the sample. Neutrals are not detected during analysis of ions be turning off the electron beam. Below: an enlargement of the orthogonal acceleration region showing representative ion trajectories. The use of two extraction grids at different voltages (dual-stage extraction) pushes the space-focus plane of ions out to the ion detector for improved mass resolution.

Image of FIG. 2.
FIG. 2.

Spectra of (left) calcite, and (right) gypsum samples using laser desorption and electron ionization. These spectra represent neutrals produced during the laser desorption that were subsequently ionized. Ions produced during the laser desorption were excluded from this analysis by the electrostatic deflection grid.

Image of FIG. 3.
FIG. 3.

Neutral (left) and ionic (right) species present at thermodynamic equilibrium for gypsum (CaSO4·2H2O), 10−3 bar total pressure, as a function of temperature, calculated using TOP20. Molecular species dominate at lower temperatures, with ionic species increasing with higher temperatures. Partial pressures are normalized for a total pressure of 1 millibar at maximum temperature.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Time-of-flight mass spectrometry of mineral volatilization: Toward direct composition analysis of shocked mineral vapor