Field ionization hydrocarbon

Del Rio, J.C. Philp, R.P. Field ionization Mass Spectrometric Study of High Molecular Weight Hydrocarbons in a Crude Oil and a Solid Bitumen. Org. Geochem. 1999, 30, 279-286. 

Scheppele, S.E. Hsu, C.S. Marriott, T.D. Benson, P.A. Detwiler, K.N. Perreira, N.B. Field-Ionization Relative Sensitivities for the Analysis of Saturated Hydrocarbons From Fossil-Energy-Related Materials. Ira. J. Mass Spectrom. Ion Phys. 1978,28, 335-346. 

Mass Spectrometry. Electron impact (El) mass spectrometry was done at NRL on the effluent from a 6 ft. OV-101 packed GC column programmed from 70 to 210°C. Field ionization mass spectrometry (FIMS) was performed by SRI International on contract to NRL. In this latter analysis, the fuel sample was frozen on a solids inlet probe prior to insertion into the mass spectrometer. The spectra accumulated for each mass during a temperature program were normally totaled for data presentation (6). Molecules boiling below 140°C are lost or depleted with this technique but such compounds comprise a very small fraction of JP-5 or DFM. Since the ionization efficiency for hydrocarbon classes is currently under study, the FIMS data are utilized primarily in a qualitative sense. 

FIMS Fingerprint. Field ionization mass spectrometry of a mixture affords a spectrum of the molecular ions since fragmentation is minimal. Thus a distribution of molecular sizes and hydrocarbon classes can be obtained from a single analysis. This is illustrated in Figure 1 which compares the FIMS fingerprints for JP-5 from Shale-I and Shale-II refining. Distinct differences can be noted. The preponderance of alkanes (C... 

Twenty previously unreported polycyclic aromatic hydrocarbons (PAHs) were synthesized by condensing mixtures of 1-phenalenone-type ketones. These PAHs were isolated and identified by using field-ionization mass spectrometry, spectrofluorometry, and UV-visible absorbance spectrometry. The spectrometry and chromatography of these and other PAHs were compared. Correlations between the steric strain and the spectral valley depths between maximums, or chromatographic retention, were found. Steric effects were not the only factors affecting retention resonance stability also appeared to increase retention. 

Lattimer, R. P, Pyrolysis field ionization mass spectrometry of hydrocarbon polymers, /. Anal Appl Pyrol, 39, 115, 1997. 

Lattimer, R. P, Direct analysis of p>ol3q)ropylene compounds by thermal desorption and pyrolysis-mass sp>ectrometry /. Anal Appl Pyrolysis, 26, 65,1993. Lattimer, R. P, Pyrolysis field ionization mass spectrometry of hydrocarbon polymers, /. Anal Appl Pyrolysis, 39,115,1997. 

Another emerging method is the coupling of GC with field-ionization MS (GG-FI-MS) [74]. Field-ionization MS yields essentially molecular ions for all hydrocarbons, except isoparaffins, with uniform sensitivities within each compound class [75]. This would gready simplify calibration since each class would require only one calibration compound. 

Scavenging experiments in hydrocarbon liquids (Rzad et al, 1970 Kimura and Fueki, 1970) tend to give low observed ionization yield, although the primary yield may be greater. The situation is similar for free-ion yield measurement under a relatively large external field. Both processes require large extrapolations to obtain the W value. 

These results imply that the use of the representative single ion-pair distribution in the ionization produced by low-LET irradiation in liquid hydrocarbons can be approximately justified even though the track itself has considerable contribution from multiple-ion-pair spurs and short tracks. It also means that even in the case of an isolated ion-pair, the long-time limit of the existence probability is perturbed by the long-range coulombic field. 

Very large branched alkanes, such as 24,24-diethyl-19,29-dioctadecylhepta-tetracontane, CgvHng, for example, pose difficulties to obtaining useful mass spectra and even 15 eV El does not anymore allow for the detection of their molecular ions. [80] Beyond C40 alkanes, especially in case of mixtures such as hydrocarbon waxes or polyethylenes of low molecular weight, field desorption and matrix-assisted laser desorption/ionization are the ionization methods of choice (Chaps. 8, 10). 

Hydrocarbon Anomalies in Soils Soil samples were collected at 200 to 500 m intervals over the Lisbon and Lightning Draw fields and analyzed for thermally desorbed Ci to C12 alkanes by Flame Ionization Detection Gas Chromatography (GC-FID) and solvent-extractable Ce to C36 aromatics by UV-fluorescence spectrophotometry. 

In summary, the distinctiveness of this soft ionization technique is that source optimization can be achieved through an independent adaptation of the ionization region, the electrical field gradient, and the gas flow. It is well suited for aromatic hydrocarbons that are selectively ionized, including nonpolar species, such as PAH, yielding to the lowest detection limits by orders of magnitude, as compared to all other API methods. 

The term ionization may refer to different processes depending on the context. For radiation effects in the gas phase, it usually implies the removal of the least bound electron to infinity. Such a theoretical definition is not feasible in the condensed phase and it is necessary use a heuristic or operational procedure. Thus, in liquid hydrocarbons, one may use the electron scavenging reaction or a conductivity current to quantify the electrons liberated from molecules. It has only been possible to extrapolate the conductivity current at a low irradiation dose and at a relatively low external field to saturation in the cases of liquefied... 

The kinetics data of the geminate ion recombination in irradiated liquid hydrocarbons obtained by the subpicosecond pulse radiolysis was analyzed by Monte Carlo simulation based on the diffusion in an electric field [77,81,82], The simulation data were convoluted by the response function and fitted to the experimental data. By transforming the time-dependent behavior of cation radicals to the distribution function of cation radical-electron distance, the time-dependent distribution was obtained. Subsequently, the relationship between the space resolution and the space distribution of ionic species was discussed. The space distribution of reactive intermediates produced by radiation is very important for advanced science and technology using ionizing radiation such as nanolithography and nanotechnology [77,82]. 

The estimation of the relative amounts of the different isotopic species of a hydrocarbon in a mixture, by means of a mass spectrometer, is usually based on the assumption that the probability of ionization of each species to form the corresponding molecule-ion is not affected by the number of hydrogen or deuterium atoms in the molecule. For example, it is assumed that equal pressures of C2H , C2D , and aU the intermediate species will give equal amounts of C2H, C2D ", etc., ions in the mass spectrometer. Field and Franklin (7) quote a considerable body of evidence which justifies the use of this assumption. The mass spectra observed have to be corrected for contributions owing to the naturally occurring heavy carbon, C, and the deuterium present in all hydrocarbons. Allowances have also to be made for the formation of fragmentary ions when these have the... 

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