A molecule ion reactor (MIR), i.e. a gas filled radio-frequency only quadrupole with a longitudinal electrical field (RFQLEF), is used as an atmospheric pressure ionization interface for an orthogonal time-of-flight mass spectrometer (O-TOFMS). A new phenomenon of selective ion 'heating' in a MIR near Mathieu's instability threshold was found and confirmed by computer simulation. The 'heating' in collisions with buffer gas molecules leads to ion decomposition. In the case of multicharged ions, fragments with an m/z value higher than that of the parent ion have a stable motion and can be analysed by an O-TOFMS. Fragmentation of bradykinin and beta-endorphin molecular ions having a selected charge state is demonstrated. The spectra show clear 'ladder' structure. The phenomenon may be used as an alternative to tandem mass spectrometry (MS/MS) for molecule structure analysis.

A concept of an "ideal" orthogonal-injection time-of-flight (O-TOF) mass spectrometer is proposed and a new high-resolution O-TOF mass spectrometer with an electrospray ion source and a molecule-ion reactor is described. The instrument design was optimized for high resolution and sensitivity using the concept of an ideal O-TOF mass spectrometer. A mass resolving power of about 20,000 (full width at half maximum) and a mass measurement accuracy in the 10 ppm range is demonstrated.

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An ion rotating excitation mode of operation of a segmented gas-filled radio-frequency quadrupole (RFQ) ion guide for a high-resolution orthogonal time-of-flight (TOF) mass spectrometer is described. It is shown theoretically, by computer simulation and experimentally, that ion rotating excitation in a gas-filled RFQ has several advantages over other types of ion oscillation excitation. The main advantages are an approximately twofold increase in average ion kinetic energy for the same maximal deviation from the RFQ axis and therefore an increase of about this factor of average internal excitation energy of ions, and the extended mass range of fragment ions that can be observed. The new method of ion decomposition by ion rotation around the axis of an RFQ ion guide was experimentally implemented and tested using a home-built`SIN-COS' generator to supply the excitation voltage. This generator enables control of phase shift and amplitude of excitation voltages applied to quadrupole rods smoothly from the data acquisition program running on a PC. Copyright # 2001 John Wiley & Sons, Ltd.As a result of the orthogonal injection of ions, 1,2 the coupling of electrospray ionization (ESI) to time-of-flight mass spectrometry (TOFMS) has now become an attractive technique, especially for structural investigation of biomolecules. Tandem mass spectrometry (MS/MS) capabilities in this case are very important and, within the last few years, the literature on ESI-TOFMS has begun to focus on MS/MS techniques with hybrid instruments. Commonly, fragmentation of ions in these systems is achieved by traditional methods for collision-induced dissociation (CID). 3±5 However, a collision cell which is often also a radio-frequency ion guide provides the intrinsic possibility of inducing of collision-induced fragmentation of selected ions by resonant excitation of ion oscillations at the auxiliary angular frequency:where q M is the Mathieu parameter, o is the fundamental angular radio frequency (RF) of the voltage applied to the quadrupole ion guide (collision cell), q is the ion charge, m is its mass, V rf is RF-amplitude, and r 0 is the radius of the radiofrequency quadrupole (RFQ), i.e. the minimal distance from axis to rods. These oscillations may be considered on average as harmonic due to the quadratic dependence of averaged effective RFQ potential (or ion`potential' energy) on the distance r av from the RFQ axis:where t v is the ion velocity relaxation time, and F is the maximal field strength at the considered point. The last approximate equality is valid for low enough gas pressure in the RFQ (when ot v ) 1) and in the vicinity of its axis. The motion of an ion in the RF-only quadrupole ion guide can be excited through the application of an auxiliary voltage on one set of pole pairs (dipolar excitation) or on two sets of these (quadrupolar excitation). In the presence of a background neutral gas, the excited ion motion will result in an increase in the number and energy of collisions. As kinetic energy is transferred to ion inter...

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