The Linkage of Data Describing Overlapping Geographical Units

A mass or energy filter or spectrometer having a known electrode configuration such as quadrupole cylindrical, monopole cylindrical or hyperboloidal wherein the electrodes are energised by a periodic or quasi-periodic time varying electrical potential the waveform of which is significantly different from a sinusoid and incorporates a zeroth harmonic term in its Fourier series. It is preferred that the waveform should be either rectangular in character or trapezoidal in character and that means should be provided for varying the duty cycle of the waveform.