Abstract
Constructing a high performance time-of-flight mass spectrometer (TOF MS) is almost equivalent to develop an ion source of high mass resolving ability and a detector of prominent timing and detection characteristics. In this research work, an electron impact ion source integrated with a compact orthogonal extraction-acceleration optics has been developed to directly minimize the “turn-around-time” spread which is believed to be the dominant contribution to the total time error of a TOF system with gaseous source, while an MCP detector with careful designs on matching the signal transmission line from the detector anode to the recorder has been developed to reduce the time distortions in the signal processing. The former instrument successfully reduces the signal width by minimizing the uncertainties in the time of ions (of same m/z) arriving the detector, while the later one effectively reduces the signal width by improving the time errors arisen inside the detector. Besides, a magnetostatic conversion plate detector of using CsI ion-electron conversion material and isochronously transporting induced secondary electrons to a Chevron arranged MCP detector has also been developed to enhance the detection efficiency especially for high mass analytes. The compact orthogonal ion source designed for the investigation of cometary gases has successfully overcome the disadvantages of conventional gaseous sources. A significant reduction in the widths of mass peaks in first time focus is obtained. An extraordinary mass resolving power of m/dm > 10000 is achieved when this source is coupled to a high performance reflectron time-of-flight mass analyzer (1.3 m long). Moreover, due to the suppression of the background count rate, the detection limits has been lowered by up to 3 orders of magnitude compared to the conventional storage sources. A dynamic range of > 10^7 is obtained with this source in a 10 s analysis time. Single-particle signal widths of well below 1 ns have been obtained with the developed fast MCP (or MSP) detectors by optimizing the geometry and some capacities of the detectors. A very sharp signal pulse with rise time of 410(+/-)20 ps and line width of 557(+/-)50 ps (FWHM) has been obtained with the MCP detector with impedance matched conical transition line between the detector anode and SMA connector. A compact detector with capacitively coupled anode and step-transition matched configuration is characterized by rise time of 420(+/-)20 ps and line width of 610(+/-)50 ps, which works well at the voltage floating range from -1 kV to +2 kV. The potential of the CsI ion-electron conversion plate detector has been investigated with an electron impact ion source. When a conventional microchannel plate detector is compared, the detection efficiency is found to be improved by a factor of ca. 1.5 at low masses (< 127u) to a factor of more than 3 at high masses (> 1000u), the dynamic range is decreased by a factor of 2-3, and the same fast timing properties are obtained with this conversion plate detector.