Mass spectroscopic ionization

The numerous reactions and physical properties that can be correlated with electronic substituent constants suggest that they reflect a basic mechanism for the effect of the substituent on the reaction or the property. Many reactions were correlated by the Hammett equation, such as electrophilic (4, 31, 32, 33), nucleophilic (4, 34) and radical (35, 36, 37). Spectroscopic properties, such as infrared and ultraviolet absorption frequencies and intensities (38). nuclear magnetic resonance shifts of various nuclei, e.g., -H, F, (39), and mass spectroscopic ionization... 

Various ionization methods were used to bombard phenol-formaldehyde oligomers in mass spectroscopic analysis. The molecular weights of resole resins were calculated using field desorption mass spectroscopy of acetyl-derivatized samples.74 Phenol acetylation was used to enable quantitative characterization of all molecular fractions by increasing the molecular weights in increments of 42. 

Mass spectroscopy is a useful technique for the characterization of dendrimers because it can be used to determine relative molar mass. Also, from the fragmentation pattern, the details of the monomer assembly in the branches can be confirmed. A variety of mass spectroscopic techniques have been used for this, including electron impact, fast atom bombardment and matrix-assisted laser desorption ionization (MALDI) mass spectroscopy. 

An inductively coupled plasma formed by passing argon through a quartz torch is widely used for the mass spectroscopic analysis of metal compounds separated by online HPLC.6 Samples are nebulized on introduction into the interface. Plasma impact evaporates solvent, and atomizes and ionizes the analyte. Applications include separation of organoarsenic compounds on ion-pairing F4PLC and vanadium species on cation exchange. 

Backstrom B, Cole MD, Carrott MJ, Jones DC, Davidson, G, et al. 1997. A preliminary study of the analysis of Cannabis by supercritical fluid chromatography with atmospheric pressure chemical ionization mass spectroscopic detection. Sci Justice 37 91. 

All values derived from mass spectroscopic measurements of ionization potentials are indeed considered to be significant measures of the energy relationships among the ionic reaction intermediates. However, further qualifications are necessary before these values may be applied to the calculation of rates of reaction in a specific catalytic system. These qualifications are yet to be developed. 

Collisional activation mass spectroscopic studies (CAMS) showed that, in the gas phase, the ethylenebenzenium ion is formed from the ionization of /3-phenylcthyl bromide or iodide (equation 62). However, ionization of the corresponding chloride gave instead protonated benzocyclobutene 105 (equation 63). The lifetime of ethylenebenzenium ion was estimated as about 10 5 s108. 

The most widely used method for quantifying FFAs is gas chromatography (GC), which has attained widespread favor due to its versatility, high sensitivity and relatively low cost. GC complexed with a flame ionization detector is used routinely to quantify FFAs, either directly or derivatized as fatty acid methyl esters (FAME). GC with mass spectroscopic detection has become the favored technique for quantification of volatile compounds derived from lipids (esters, lactones, ketones, alcohols and acids). 

A Time-of-Flight Mass Spectroscopic Study in Combination with One-Photon Ionization... 

The apparatus for the TOF mass spectroscopic measurement is shown schematically in Figure 9.1. A rotating graphite rod (I cm in diameter, C C = 98.9% 1.1%) was ablated in a vacuum chamber by the second harmonics of a Q-switched Nd YAG laser (Spectra-Physics DCR-11, 532 nm, 7 ns duration, 7.1 mJ/pulse). The ablation laser pulse was loosely focused with a lens of a focal length of 25 cm. The ablated products were introduced into the ionization region by a pulsed buffer gas flow of H2/He. The back-pressure of the buffer gases was set at 15atm (1.52 x 10 Pa) to... 

---