A residual gas analyser is an instrument which, by ionising the ambient gas under low pressure (<10” atm), enumerates the different atomic elements in the gas and measures their relative abundance. The analysis of the gas is done using a mass spectrometer, which identifies the atomic elements by separating the atoms, group of atoms or molecules according to their mass to charge ratio. Mass spectrometers are classified on the basis of how the atomic mass separation is accomplished. In a time-of-flight mass spectrometer the mass separation is achieved by injecting a mono-energetic ion beam, into a long electric/magnetic field free tube. The time taken to reach the end of the tube depends on the square root of the ions mass to charge ratio and so by observing the output times of whatever ions are present, the different atomic elements are revealed. The relative abundance of the elements is simply the ratio of the number of ions egressing the tube at the specific times. This thesis describes the work carried out on the development of a new type of time-of-flight mass spectrometer for the purposes of residual gas analysis and was funded by Eolas, the Irish science and technology agency. Like the conventional type it uses a field free flight tube, however the tube is used more as a delay line rather than as the mass separator. The mass separation is achieved using a combination of time varying accelerating / decelerating electric fields at the start and end of the tube. The voltages producing these electric fields are between 0 and -200 volts D.C. and between 100 and 300 volts peak to peak A.C. at a frequency of 40 to 50kHz. The resolution obtained with the mass spectrometer is approximately ± 0.5 atomic mass units.