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.

Numerical simulations of a gas flow through a capillary being a part of mass spectrometer atmospheric interface were performed using a detailed laminar flow model. The simulated interface consisted of atmospheric and forevacuum volumes connected via a thin capillary. The pressure in the forevacuum volume where the gas was expanding after passing through the capillary was varied in the wide range from 10 to 900 mbar in order to study the volume flow rate as well as the other flow parameters as functions of the pressure drop between the atmospheric and forevacuum volumes. The capillary wall temperature was varied in the range from 24 to 150 °C. Numerical integration of the complete system of Navier-Stokes equations for a viscous compressible gas taking into account the heat transfer was performed using the standard gas dynamic simulation software package ANSYS CFX. The simulation results were compared with experimental measurements of gas flow parameters both performed using our experimental setup and taken from the literature. The simulated volume flow rates through the capillary differed no more than by 10% from the measured ones over the entire pressure and temperatures ranges. A conclusion was drawn that the detailed digital laminar model is able to quantitatively describe the measured gas flow rates through the capillaries under conditions considered. Graphical Abstract ᅟ.

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...

The possibility of the application of the electromembrane technique for production of ions of biological molecules at atmospheric pressure is demonstrated. This technique has previously only been used for extraction of ions from liquids directly into vacuum. The membrane technique for ion extraction at atmospheric pressure was tested with both time-of-flight and Fourier transform ion cyclotron resonance mass spectrometers. The mass spectra of intact molecular ions obtained from aqueous solutions of peptides and proteins are presented. The possible mechanisms of non-destructive ion extraction are discussed. The new technique is promising for achieving absolute sensitivity (charging every analyte molecule) and for performing spatially-resolved analysis of liquid biological samples.

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