Wiley-McLaren instruments

In the Wiley McLaren instruments produced for many years by the Bendix Corporation (Rochester, NY, USA) the mass-dependence problem was addressed by scanning the delay time, bringing a different mass into focus in... 

An example of a Fourier transform TOF mass spectrum of toluene obtained from this instrument is shown in Figure 7.3. Their overall duty cycle of 25% is considerably greater than that of the Wiley-McLaren design for electron impact ionization. 

Passive Ion Storage. The IRLD instrument was constructed from a modified CVC Products (Rochester, NY) model 2000 time-of-flight mass spectrometer, a Wiley-McLaren design that included a pulsed electron beam. When used in the electron impact (El) ionization mode it was possible to monitor the NJ ion signal as a fimction of the electron-beam pulse width from 0.1 ps (where the signal was proportional to the pulse width) to 3 (is (where losses due to ion drift from the source equal the rate of ion production). From this, one could determine the rate of ion loss from the extraction volume due to drift at thermal energies. For the N2 ion (wj/z = 28) the half-life in the extraction volume was about 1 ps. Since the drift velocity is ... 

The best performance of TOF instruments is now achieved by a combination of an electrostatic reflector and the Wiley-McLaren focusing techniques, and this combination is the basis for most high-performance TOF systems. 

To reduce the kinetic energy spread among ions with the same m/z ratio leaving the source, a time lag or delay between ion formation and extraction can be introduced. The ions are first allowed to expand into a field-free region in the source and after a certain delay (hundreds of nanoseconds to several microseconds) a voltage pulse is applied to extract the ions outside the source. This mode of operation is referred to as delayed pulsed extraction to differentiate it from continuous extraction used in conventional instruments. Delayed pulsed extraction, also known as pulsed ion extraction, pulsed extraction or dynamic extraction, is a revival of time-lag focusing, which was initially developed by Wiley and McLaren in the 1950s, shortly after the appearance of the first commercial TOF instrument. 

An important contribution to analyzing DNA with MALDI-TOF is also the introduction of delayed extraction instruments by Wiley and McLaren [33]. Compared to static extraction, which employs a permanent electrical field for ion acceleration, the delayed extraction accumulates ions over a time range of some... 

Wiley WC and McLaren IH (1955) Time-of-flight mass spectrometer with improved resolution. Review of Scientific Instrumentation 26 1150-1157. 

Temporal Distributions. These include actual distributions in the time of ion formation as well as limitations of ion-detection and time-recording devices. The classical example of the former was the 1955 instrument of Wiley and McLaren in which ions were formed in the gas phase by a pulsed electron beam with a pulse width of 1 to 5 ps. In this case, temporal focusing was achieved by forming the ions... 

TOF instruments were first designed and constructed starting in the late 1940s. Key advances were made by William C. Wiley and I.H. McLaren of the Bendix... 

Cameron and Eggers introduced their velocitron, an instrument with a Nier electron impact source, a 317-cm drift tube, and oscilloscope recording. Ions were accelerated to a constant energy of 500 eV, so that their velocities would be inversely proportional to the square root of their masses. The 1955 instrument by Katzenstein and Friedland pulsed both the ionizing electron beam and the ion extraction field, using a drawout (orpushout) pulse. A pulsed extraction approach was also developed by Wiley and McLaren as ameans to improve mass resolution. Their instrument was commercialized, and their approach is the forerunner of the current delayed extraction methods used in MALDl. 

---