High temperature mass spectrometer

The gaseous molecule PtC2 has been observed in a high-temperature mass spectrometer and its atomization energy determined.172... 

The dissociation energy of the AgSe(g) molecule was determined by Smoes, Mandy, Auwera-Mahieu and Drowart [72SMO/MAN] from high temperature mass spectromet-ric measurements of the ion intensities of the participating species. The dissociation... 

NASA GRC facilities to study hot corrosion include Mach 0.3 burner rigs and a high-pressure burner rig, a high-temperature mass spectrometer (one of the two in the country) to study chemistry of salt deposition, and a multitude of laboratory rigs, including microbalances, to study hot corrosion under controlled atmospheres. 

The thenuodynamic quantities are derived from equilibrium measurements as a fiinction of temperature. The measurements are frequently made in a high-pressure mass spectrometer [107]. The pertinent equation is In... 

The low-voltage, high-resolution mass spectra (LVHRMS) were obtained on a Kratos MS-50 high-resolution mass spectrometer interfaced to a Kratos DS-55 data system. The Rasa coal extract was vaporized directly into the ion source by a direct-insertion probe. Spectra were recorded at probe temperatures of 100°C, 200OC, 300°C, and 350°C. The instrument was scanned from 700 to 60 amu at a scan... 

Volatiles isolated by the purge-and-trap method were analyzed by GC-MS using a Varian 3400 gas chromatograph coupled to a Finnigan MAT 8230 high resolution mass spectrometer equipped with an open split interface. Mass spectra were obtained by electron ionization at 70 eV and an ion source temperature of 250°C. The filament emission current was 1 milliampere and spectra were recorded on a Finnigan MAT SS 300 Data system. 

Concerning the first field of application, the kinetics and equilibrium constants for several halide transfer reactions (equation 1) were measured in a pulsed electron high pressure mass spectrometer (HPMS)4 or in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR)5. From measurements of equilibrium constants performed at different temperatures, experimental values were obtained for the thermochemical quantities AG°, AH° and AS° for the reaction of equation 1. The heat of formation (AH°) of any carbocation of interest, R+, was then calculated from the AH0 of reaction and the AH° values of the other species (RC1, R Cl and R +) involved. 

The 1960s brought two major advances in the discipline of ion energetics and stmcture. The development of high-pressure mass spectrometer ion sources led by Kebarle and co-workers allowed the measurement of equilibrium constants for gas-phase ionic systems at well-specified temperatures and, from temperature-dependent studies, the enthalpy and entropy changes associated with gas phase equilibria. These concepts provided the foundation for current studies of molecular recognition in the gas phase. 

Gas chromatography-mass spectrometry. The two GC-MS systems used were (a) A Varian MAT-731 high resolution mass spectrometer operated at 1000 RP, 8 KV, 70eV and source temperature of 250 C. 

A connnon approach has been to measure the equilibrium constant, K, for these reactions as a fiinction of temperature with the use of a variable temperature high pressure ion source (see section (Bl.7.2)1. The ion concentrations are approximated by their abundance in the mass spectrum, while the neutral concentrations are known from the sample mlet pressure. A van t Hoff plot of In K versus /T should yield a straight Ime with slope equal to the reaction enthalpy (figure B1.7.11). Combining the PA with a value for basicityG at one temperature yields a value for A.S for the half-reaction involving addition of a proton to a species. While quadnipoles have been tire instruments of choice for many of these studies, other mass spectrometers can act as suitable detectors [19, 20]. 

A further consequence of the high temperatures is that much of the sample is simply evaporated without producing isolated positive ions. There is a competition between formation of positive ions and the evaporation of neutral particles. Since the mass spectrometer examines only isolated charged species, it is important for maximum sensitivity that the ratio of positive ions to neutrals be as large as possible. Equation 7.1 governing this ratio is given here. 

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