ABSTRACT
The use of radiofrequency (RF) quadrupole elds for mass spectral analsysis was invented by Wolfgang Paul and others in the 1950s. The method can be implemented as a linear, two-dimensional (2D) electrode array, in the quadrupole and the monopole, or as a three-dimensional (3D) ‘ion trap,’ comprising a ring electrode and two end-cap electrodes. The monopole has never been developed as an analytical instrument, and while the quadrupole mass spectrometer grew rapidly in terms of performance and range of applications, it was only with the introduction of the
4.1 Introduction ................................................................................................. 273 4.2 Ion Motion in a Rectangular Wave Quadrupole Field ................................ 276 4.3 Secular Motion and the Pseudopotential Well ............................................ 279 4.4 Digital Asymmetric Waveform ...................................................................284 4.5 Digital Frequency Scan and Extended Mass Range for
High Mass Detection ...................................................................................285 4.6 Non-Stretched Geometry and Field-Adjusting Electrode ...........................286 4.7 Mass Resolution ..........................................................................................290 4.8 Forward and Reverse Scanning .................................................................. 291 4.9 Scan Direction and Space Charge ............................................................... 295 4.10 Precursor Ion Isolation ................................................................................ 298 4.11 Tandem Mass Spectrometry in Conjunction with Electron Capture
Dissociation (ECD) .....................................................................................299 4.12 Digital Linear Ion Trap ...............................................................................302 4.13 Conclusion ...................................................................................................305 References ..............................................................................................................306
mass-selective instability scan mode [1] three decades later that the ion trap became a powerful and inexpensive alternative to other mass analyzers, exploiting its high mass resolution and high sensitivity for the analysis and detection of high mass compounds. A periodically-alternating quadrupole eld is generated by application of RF and direct current (DC) voltages to appropriate electrodes. Under the inuence of the quadrupole eld, ions with different mass-to-charge ratios undergo stable or unstable oscillations, achieving either connement within the trap or ejection. Since the development of the axial resonant modulation technique, the performance of the 3D quadrupole ion trap has been improved dramatically, transforming this mass spectrometer, originally introduced as a simple gas chromatography (GC) detector, into a much more versatile analytical tool. Ion traps combine ion storage with mass analysis, exhibiting an acceptable mass (m/z) range, applicable even for the analysis of high mass biomolecules, mass resolution up to 1 × 105, and with high sensitivity [2]. In addition, ion isolation followed by multi-stage tandem mass spectrometric analysis (MSn) [3] via collisional-induced dissociation (CID), ion/ion electron transfer dissociation (ETD) [4], or electron capture dissociation (ECD) [5] can provide additional structural information on the analyte of interest.
