Magnetic techniques, detect ordering

A variety of pulsed techniques are particularly useful for kinetic experiments (Mclver and Dunbar, 1971 McMahon and Beauchamp, 1972 Mclver, 1978). In these experiments, ions are initially produced by pulsing the electron beam for a few milliseconds. A suitable combination of magnetic and electric fields is then used to store the ions for a variable period of time, after which the detection system is switched on to resonance to measure the abundance of a given ionic species. These techniques allow the monitoring of ion concentration as a function of reaction time. Since the neutrals are in large excess with respect to the ions, a pseudo first-order rate constant can be obtained in a straightforward fashion from these data. The calculation of the rate constant must nevertheless make proper allowance for the fact that ion losses in the icr cell are not negligible. 

Consideration must be given to the quantity of sample needed for the minimum detection ]imits of the instrumental technique used. A number of techniques have been ranked in order of increasing amounts of material needed as follows mass spectroscopy (1 - 10 yg), chemical spot tests (1 - 100 yg), infrared and ultraviolet spectroscopy (10 - 200 yg), melting point (0.1 -1 mg), elemental analysis (0.5 - 5 mg), boiling point (1 - 10 mg), functional group analysis (1 - 20 mg), and nuclear magnetic resonance spectroscopy (1-25 mg). 

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