An ion mobility/mass spectrometry technique has been developed to record mass-resolved ion mobility distributions for multiple ions simultaneously. The approach involves a new instrument that couples an electrospray ion source to an injected-ion drift tube/time-of-flight mass spectrometer. Individual components in a mixture of ions are separated by mobility differences in a drift tube and subsequently dispersed by mass-to-charge ratios in a time-of-flight instrument. Flight times in the mass spectrometer are much shorter than residence times in the drift tube, making it possible to record mass-resolved ion mobilities for all ions simultaneously. The result is a three-dimensional spectrum that contains collision cross section, mass-to-charge, and ion abundance information. The instrument and data acquisition system are described. Examples of combined ion mobility/time-of-flight data are presented for distributions of electrosprayed bradykinin and ubiquitin ions.

A linear octopole trap interface for an ion mobility time-of-flight mass spectrometer has been developed for focusing and accumulating continuous beams of ions produced by electrospray ionization. The interface improves experimental efficiencies by factors of approximately 50-200 compared with an analogous configuration that utilizes a three-dimensional Paul geometry trap (Hoaglund-Hyzer, C. S.; Lee, Y. J.; Counterman, A. E.; Clemmer, D. E. Anal. Chem. 2002, 74, 992-1006). With these improvements, it is possible to record nested drift (flight) time distributions for complex mixtures in fractions of a second. We demonstrate the approach for several well-defined peptide mixtures and an assessment of the detection limits is given. Additionally, we demonstrate the utility of the approach in the field of proteomics by an on-line, three-dimensional nano-LC-ion mobility-TOF separation of tryptic peptides from the Drosophila proteome.

We report the implementation of covariance mapping mass spectmscopy to pulsedelectrowbeam ionization time-of-flight mass spectroscopy. The technique has been applied .~..

Absolute cross sections for electronimpact ionization and dissociative ionization of the SiF free radicalA new electron impact spectrometer has been constructed that utilizes a variable energy (4-500 eV) pulsed electron source with time-of-flight detection of electrons and ions. The apparatus can be used in a beam-beam scattering mode or in a constant pressure mode suitable for absolute measurements. A newly designed data processing system is described that uses standard CAMAC modules (LeCroy model 4208 TDCs) and allows up to 32 separate detectors to be used simultaneously in a singie hit mode or up to four separate detectors in a multihit mode with each detector capable of recording up to eight hits in the same experiment. The dead time between experiments is 9.2 pus which allows up to 100 000 experiments/s for experimental flight times not exceeding 1 ~LS at 1 ns timing resolution. Longer flight times, up to 8.3 ms in duration, can be accommodated but with reduced timing resolution. The determination of the partial ionization cross sections for Ar+, Ar2 + , and Ar3 + from threshold up to 500 eV is used as an illustration of some of the capabilities of the new instrument. The results obtained are in excellent agreement with other recent work for Ar + . For the multicharged ions the cross sections were found to lie between earlier reported results. In addition the utility of the variable ion extraction field capability of the instrument is demonstrated by the separation of N + from N:+ for the case of electron impact dissociative ionization of N2. A new method for placing the data on an absolute scale is presented.

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