Early development of time-resolved mass spectrometry

In the paper that introduced FPTRMS [1], as well as early work from other laboratories, it is amply recorded that the experiments were hampered by low sensitivity, and it is apparent from reading those works that the amount of useful information was limited. Modern instrumentation and techniques of data aquisition and analysis have largely overcome the sensitivity problem, so that today mass spectrometry is a versatile and reliable technique for accurate studies of kinetics and mechanism. The sensitivity has improved to the point where free radicals can be detected at low enough concentrations that their reactions can be studied in the absence of radical-radical interactions that would otherwise complicate the kinetic analysis. Among modern methods for experimental chemical kinetics of gas reactions, FPTRMS has much to offer and should be seriously considered when evaluating alternative methods for kinetics investigations. 

EARLY DEVELOPMENT OF TIME-RESOLVED MASS SPECTROMETRY 

The experiments of Kistiakowsky and Kydd [1] were done by single-pulse photolysis with a 500-J flashlamp, the reaction vessel contents being sampled via a pinhole leak into the electron ionization source of a Bendix time-of-flight (TOF) mass spectrometer. Mass spectra were obtained by pulsed extraction of ions from the ion source at 50-fis intervals after the flash. The signal from the electron multiplier detector was displayed on a cathode ray tube, which was photographed with a rotating drum camera. 

The smaller peaks in the mass spectra showed random fluctuations in the number of ions formed in the interval between consecutive pulses. The fluctuations were smoothed by performing several experiments at the same conditions and averaging peak heights from spectra taken at the same time interval after the flash. The time dependence of individual peaks was determined by ratioing the peak height of an m/z signal of interest to the peak height at m/z = 20, due to Ne+ from deliberately added Ne. The Ne, of course, does not participate in the reaction and its concentration is time invariant. 

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II. EARLY DEVELOPMENT OF TIME-RESOLVED MASS SPECTROMETRY... 

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