Mass spectrometer. Sample tray of a timeof flight secondary ion mass spectrometer (ToF SIMS) viewed through a porthole in the spectrometers casing. This mass spectrometer analyses the surface of a sample. A pulsed ion beam removes molecules from the outermost surface of the sample and converts them to ions. This is done at low intensity so that large or macro molecules, such as polymers, stay intact. The ions are taken up into a flight tube and accelerated toward a detector. The time taken to reach the detector determines the mass of the ion. This mass spectrometer helps to accurately determine the chemical composition of a samples surface.