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|Title:||Determination of High Mass, Low Intensity and Transient Mass Spectra by Computer|
|Author(s):||Snelling, Charles Robert, Jr.|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||The need for a reference standard of high molecular weight for field desorption (FD) mass spectrometry earlier led to the proposal of hexakis(multifluoroalkoxy)cyclotriphosphazenes as standards. The phosphazenes tend to give only molecular ions in the FI/FD mode. Their peaks' negative mass defects rarely interfere with sample peaks at high or low resolution while their volatility at low temperatures, even for compounds of molecular weight 3300, provides a minimum source memory effect.
Binary mixtures of these phosphazenes have been developed that individually cover a mass range of 300 amu and have been used successfully for high resolution peak matching in EI, CI and FI/FD modes. When combined, these mixtures facilitate the computer acquisition of both low and high resolution EI, CI, FI/FD and FAB spectra in the mass range of 700-3300 amu.
Several problems in mass spectrometry are amenable to solution by the use of a computer to acquire and sum multiple scans. One of these involves obtaining useful data from the low-intensity spectra inherent in both low and high resolution field desorption (FD) and in high resolution electron impact (EI) mass spectrometry. Another problem solved by multiple scans involves spectra that change with time or are only present for a short period of time such as those frequently encountered in GC/HRCI and GC/EI isotope ratio studies.
To deal with these problems, we have developed a hardware/software multichannel signal averager (MSA) system using ion counting techniques. The MSA system is based on a commercially available pulse analyzer system but is more versatile since all data handling is performed by software. The system permits real-time acquisition and observation of multiple scans for averaging and is designed for both low resolution and high resolution determinations, including assignment of elemental compositions.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.
|Date Available in IDEALS:||2014-12-15|