Quadrupole ion trap

From Freepedia

A quadrupole ion trap (also known as a Paul trap, QIT, twisted quadrupole ion trap or sometimes just ion trap) refers to an ion trap that uses static and radio frequency (RF) ~1MHz oscillating AC electric fields to trap ions as well a mass spectrometer that uses such a trap to analyze ions. The invention of the quadrupole ion trap itself is attributed to Wolfgang Paul who shared the Nobel Prize in Physics in 1989 for this work.

Theory

The trap itself generally consists of two hyperbolic metal electrodes with their focii facing each other and a hyperbolic ring electrode halfway between the other two electrodes. The ions are trapped in the space between these three electrodes by AC ~1MHz and DC (non-oscillating, static) electric fields. The AC radio frequency voltage oscillates between the two hyperbolic metal electrodes at the 'top' and 'bottom' of the trap ('top' and 'bottom' are in phase) and the hyperbolic ring electrode that forms the 'side' of the trap. The ions are first pulled up and down axially while being pushed in radially. The ions are then pulled out radially and pushed in axially (from the top and bottom). In this way the ions move in a complex motion that generally involves the cloud of ions being long and narrow and then short and wide, back and forth, oscillating between the two states.

External links

• Nobel Prize in Physics 1989