With the development of mass spectrometry (MS) instruments starting in the late 19th century, more and more research emphasis has been put on MS related subjects, especially the instrumentation and its applications. Instrumentation research has led modern mass spectrometers into a new era where the MS performance, such as resolving power and mass accuracy, is close to its theoretical limit. Such advanced performance releases more opportunities for scientists to conduct analytical research that could not be performed before. This thesis reviews general MS history and some of the important milestones, followed by introductions to ion cyclotron resonance (ICR) technique and quadrupole operation. Existing electronic designs, such as Fourier-transform ion cyclotron resonance (FT-ICR) preamplifiers (for ion signal detection) and radio-frequency (RF) oscillators (for ion transportation/filtering) are reviewed. Then the potential scope for improvement is discussed. Two new FT-ICR preamplifiers are reported; both preamplifiers operate at room temperature. The first preamplifier uses an operational amplifier (op amp) in a transimpedance configuration. When a 18-k feedback resistor is used, this preamplifier delivers a transimpedance of about 85 dB , and an input current noise spectral density of around 1 pA/ p Hz. The total power consumption of this circuit is around 310 mW when tested on the bench. This preamplifier has a bandwidth of fi3 kHz to 10 MHz, which corresponds to the mass-to-charge ratio, m/z, of approximately 18 to 61k at 12 T for FT-ICR MS. The transimpedance and the bandwidth can be adjusted by replacing passive components such as the feedback resistor and capacitor. The feedback and bandwidth limitation of the circuit is also discussed. When using an 0402 type surface mount resistor, the maximum possible transimpedance, without sacrificing its bandwidth, is approximated to 5.3 M . Under this condition, the preamplifier is estimated to be able to detect ~110 charges. The second preamplifier employs a single-transistor design using a different feedback arrangement, a T-shaped feedback network. Such a feedback system allows ~100-fold less feedback resistance at a given transimpedance, hence preserving bandwidth, which is beneficial to applications demanding high gain. The single-transistor preamplifier yields a low power consumption of ~5.7 mW, and a transimpedance of 80 dB in the frequency range between 1 kHz and 1 MHz (m/z of around 180 to 180k for a 12-T FT-ICR system). In trading noise performance for higher transimpedance, an alternative preamplifier design has also been presented with a transimpedance of 120 dB in the same frequency range. The previously reported room-temperature FT-ICR preamplifier had a voltage gain of about 25, a bandwidth of around 1 MHz when bench tested, and a voltage noise spectral density of ~7.4 nV/ p Hz. The bandwidth performance when connecting this preamplifier to an ICR cell has not been reported. However, from the transimpedance theory, the transimpedance preamplifiers reported in this work will have a bandwidth wider by a factor of the open-loop gain of the amplifier. In a separate development, an oscillator is proposed as a power supply for a quadrupole mass filter in a mass spectrometer system. It targets a stabilized output frequency, and a feedback control for output amplitude stabilization. The newly designed circuit has a very stable output frequency at 1 MHz, with a frequency tolerance of 15 ppm specified by the crystal oscillator datasheet. Within this circuit, an automatic gain control (AGC) unit is built for output amplitude stabilisation. A new transformer design is also proposed. The dimension of the quadrupole being used as a mass filter will be determined in the future. This circuit (in particular the transformer and the quadrupole connection/mounting device) will be finalised after the design of the quadrupole. Finally, this thesis concludes with a discussion between the gain and the noise performance of an FT-ICR preamplifier. A brief analysis about the correlation between the gain, cyclotron frequency, and input capacitance is performed. Future work is also suggested for extending this research.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:575003 |
| Date | January 2012 |
| Creators | Lin, Tzu-Yung |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/55048/ |
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