Negative ion chemical ionization in a quadrupole ion trap using reagent anions injected from an external ion source

Abstract

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.