A novel aircraft-based tandem mass spectrometer for atmospheric ion and trace gas measurements

Abstract

A novel aircraft-based triple-quadrupole mass spectrometer (TQMS) has been developed for improved detection and collisional analysis of atmospheric ions and trace gases. The instrument is also suitable for laboratory collision-induced dissociation (CID) measurements, studies of ion–molecule reactions, and analytical applications. Highly sensitive and selective trace gas detection by chemical ionization mass spectrometry (CIMS) methods is also possible using a novel ion injection technique. Unambiguous identification of atmospheric ions is possible by comparing atmospheric fragment ion spectra with the fragment ion spectra of known ions measured in the laboratory under conditions similar to those of the aircraft-based CID measurement. The overall efficiency of the CID process, that is, the ratio of the fragment ion signal in the CID mode and the signal of the parent ion in the normal mass scan mode, varies between some 10−3 and 5×10−2, depending on the mass resolution of the mass selecting and mass analyzing quadrupoles. The sensitivity for ambient ion measurements is about a factor of 3 larger compared to previous aircraft-borne measurements. The TQMS was successfully used on five aircraft flights between September 27 and October 2 1991. The identification of various atmospheric ions was investigated by CID and the concentrations of various atmospheric trace gases including nitric acid, sulfuric acid, sulfur dioxide, acetone, and acetonitrile were measured by CIMS. In this article, the novel chemical ionization-triple quadrupole mass spectrometer is described and its potential is illustrated by describing the detection and unambiguous identification of atmospheric acetone.