Trapping instruments
In these instruments, ions in a continuous beam are trapped in three-dimensional electric fields. The trapped ions are ejected one after another by application of an additional electric field and are analysed to produce a mass spectrum. Ion trap instruments are compact, versatile and highly automated, but in practice the accuracy and resolution achieved by these instruments do not reach the level of quadrupole instruments.

Another version of the trapping principle is employed in Fourier transform ion cyclotron MS (FTMS). It involves trapping of ions formed by EI, CI, MALDI and ESI and makes use of Fourier transform for simultaneous detection of a wide-range of masses. The method has the highest resolving power in mass spectrometry, a high upper mass limit, high sensitivity, nondestructive detection, and high accuracy for mass measurements.