Time-of-Flight Mass Spectrometry

Abstract

As shown in Table I, time-of-flight mass spectrometry has had a checkered history since it became commercially available following the innovations of the Wiley-McLaren design in 1955. The Bendix/CVC instruments were used for a wide range of applications facilitated by its very fast scan capability and/or ease of access to the ion source. However, because they were seen as having both low resolution and low sensitivity, these instruments never became widely utilised in the major areas of mass spectrometry. The resurgence of interest in the time-of-flight technique since the mid '80's has been due to the advent at the forefront of mass spectrometry development of such techniques as laser and plasma desorption, laser ionisation and surface analysis, which require its ability to provide a complete spectrum for each ionisation event and also its unlimited mass range. In order for this renaissance to continue and expand, a wide base of commercially available instruments is required. As can be seen from Table II such a base now exists. This chapter is intended to provide a brief history of the time-of-flight mass spectrometer (TOFMS) over the period 1955-90 based on the progress reported at various European time-of-flight symposia. In this it is intended to act as a prelude to the exciting developments which this author anticipates for the current decade. The following chapters will provide the reader with a foretaste of the future of time-of-flight mass spectrometry. Time-of-flight mass spectrometers operate on the simple principle that a packet of ions, of differing mass/charge (m/z) ratios but equal energy or momentum, when projected into a constant electric field will separate according to their m/z ratios. Since ζ is usually unity, the separation is essentially one of mass. If the ions travel a fixed distance / to a detector, then the 'time-of-flight' (TOF) is given by