Development and characterization of an ion trap mass spectrometer for the on-line chemical analysis of atmospheric aerosol particles

A novel Ion Trap Aerosol Mass Spectrometer (IT-AMS) for atmospheric particles has been developed and characterized. With this instrument the chemical composition of the non-refractory component of aerosol particles can be measured quantitatively. The set-up makes use of the well-characterized inlet and vaporization/ionization system of the Aerodyne Aerosol Mass Spectrometer (AMS). While the AMS uses either a linear quadrupole mass filter (Q-AMS) or a time-of-flight mass spectrometer (ToF-AMS) as the mass analyzer, the IT-AMS utilizes a three-dimensional quadrupole ion trap. The main advantages of an ion trap are the possibility of performing MSn-experiments as well as ion/molecule reaction studies. The mass analyzer has been built in-house together with major components of the electronics. The IT-AMS is operated under full PC control and can be used as a field instrument due to its compact size. A detailed description of the set-up is presented. Experiments show that a mass resolving power larger than 1500 can be reached. This value is high enough to separate different organic species at m/z 43. Calibrations with laboratory-generated aerosol particles indicate a linear relationship between signal response and aerosol mass concentration. These studies, together with estimates of the detection limits for particulate sulfate (0.65 μg/m3) and nitrate (0.16 μg/m3) demonstrate the suitability of the IT-AMS to measure atmospheric aerosol particles. An inter-comparison between the IT-AMS and a Q-AMS for nitrate in urban air yields good agreement. For laboratory-generated polystyrene latex particles a MS/MS-study using collision-induced dissociation (CID) with a daughter/parent ion yield of more than 60% has been performed. In the future, similar MS/MS-studies can be conducted for atmospheric particles and for the study of secondary aerosol formation in smog chamber experiments.