The factors that influence the sensitivity and detection limits under electron ionization (EI) and chemical ionization (CI) conditions in an ion trap mass spectrometer have been examined. It was found that for benzophenone, EI had a three times lower detection limit than CI, and EI was approximately three times more sensitive for the detection of the molecular species. When sensitivities were compared on the basis of total ion current detected, using equal duty cycles, EI was observed to be fifteen times more sensitive than CI. Selected reagent ion CI is shown, by defining the kinetic as well as thermodynamic aspects of the ion/molecule reactions in the ion trap, to be particularly useful in sensitivity studies and should be exploited for certain analyses.

Low-energy (<10 eV) positrons have been used to ionize organic molecules in the gas phase followed by mass spectrometric analysis. High-energy positrons from a linear electron accelerator-based facility are re-moderated to less than 3 eV and trapped in a miniature Penning trap where they interact with the target molecules. Ions thus formed are mass analyzed in a time-of-flight mass spectrometer. The predominant ionization mechanism in this energy regime involves positronium formation and the spectra are comparable to electron impact spectra at energies a few eV above the ionization energy of the molecules.

Negative ion chemical ionization is demonstrated in an ion trap mass spectrometer using reagent anions formed in an external ion source and injected into the ion trap. In cases where the major anions formed in the ion source are the reagent anions of choice, the ion trap can be filled to capacity in a few milliseconds. Times several orders of magnitude longer are typically required using the conventional ionization method in the ion trap to accumulate reagent anions. Selected reagent anion chemical ionization is demonstrated using methods available with the ion trap to isolate ions of particular mass/charge values. Reagent anion selection gives greater control over the ionization mechanism(s) than is afforded by conventional high pressure chemical ionization methods. Experiments with a low vapor pressure compound admitted via a solids probe indicate that the analytical performance achievable using reagent anion injection into the ion trap in an optimized system should be comparable to those obtained with positive chemical ionization in an ion trap.

Time-resolved ion momentum spectrometry is a technique that combines magnetic sector and time-of-flight analyzers to give energy-independent mass determination, enabling seperation of parent ions and products of metastable or collisionally activated dissociations. In the time-resolving stage of this mass spectrometer, ion packet formation by beam deflection is shown to be superior to that formed by ion source pulsing with simultaneous time and momentum resolutions of 650 and 500, respectively. Loss in detectability over that obtained using the magnetic sector without time resolution is only a factor of 65, despite using only 0.01% of the continuous beam. Precise beam intensity profiles as a function of magnetic field strength and arrival time are obtained.