Application Note and Selection Chart for Time-Of-Flight Mass Spectrometry

Instrumentation by FAST ComTec

Part II Electro-Spray Mass Spectrometry by Universität Karlsruhe, Institut für Physikalische Chemie, Lehrstuhl für die Physikalische Chemie Mikroskopischer Systeme

An Electrospray Mass Spectrometer is used to analyze Cytochrome C
The analyte is dissolved in a water/methanol solution. Ions are generated by electrospraying this solution. The ion beam is then injected into an orthogonal linear time-of-flight mass spectrometer.
The ion-optics consist of three parallel plates (Wiley-McLaren principle), one is at ground the two others carry the acceleration voltage of 6.000 V and 5.790 V respectively.
The interesting part of the Cytochrome C spectrum is recorded between time bins 20.000 and 42.000. The most intensive peakis at time bin 29.740 and represents Cytochrome C with a charge of +14 i.e. m/z of approximately 885 (z is the charge state).

The ions will be directed by deflection plates to the MCP detector. In the field free drift tube of 2.1 m lengths the ions are focussed by an electrostatic ion lens.
At the end of the flight tube a dual microchannel plate detector records the arriving ions. As the flight time of the ions is a function of their mass, the heavier the mass of the ions the longer they will take to reach the detector.

The output of the detector is connected to a FAST ComTec Amplifier/Discriminator Model 7011. Setting the threshold of the discriminator just above the noise level assures that valid stop pulses are recorded only. The Fast-NIM output of the 7011 is connected to the FAST ComTec Model 7886E, a multistop TOF/multiscaler with 500 ps time resolution.

The advantage of this unit is the large dynamic range which can easily cover the time range of between 10 and 21 usec.