The principle of the linear time-of-flight mass spectrometer is shown below. Neutral analyte molecules pass the scimmer and the extraction volume of the mass spectrometer. The analyte molecules are ionized in the extraction volume and accelerated along the axis of the mass spectrometer. To compensate the initial transverse velocities, a ramp voltage is applied to the deflection plates. This ramp effectively puts the analyte ions on a path parallel to the axis of the mass spectrometer.

In case the laser beam ionizes some unwanted ions from the residual gas in the mass spectrometer, these ions will not reach the detector, because their initial velocity is essentially zero, yet they also are deflected by the voltage ramp applied to the deflection plates. Thus the unwanted ions are blocked by the sides of the aperture.

Specifications: