Question

With the aid of a simple schematic describe the principle of operation of a linear time of flight mass analyzer (LTOF).

Answer 1

time of flight mass analyzer differs from another mass analyzers is a way that the separation occurs because of the different time required by the ions to reach the detector. this difference in the time is function of mass of each ion. There is no influence of any external field to propel the ions. The initial acceleration voltage gives same kinetic energy to all the ions but later the mass of each ion determines the time to reach the detector.

In simple terms, lighter ions will reach the detector first and the heavier ones will take longer time.

The acceleration plate is used to give kinetic energy to the ions. Slit is used to focus the ions through the flight tube. Flight tube is a hollow tube maintained under vacuum for the ions to drift according to their velocities based on their masses. The detector usually is a electron multiplier for ion detection.

The dynodes are set of cathodes/anodes maintained at increasing voltages. These increasing voltages causes ions to multiple manifold giving an amplified results.

Before the acceleration area, the ionization source used is that of laser ionization. Ionization is a process in which the molecule is excited. The excited molecule gives away an electron and gets converted into an positively charged ion.