Multipole ion guide for mass spectrometry

An apparatus for analyzing chemical species, comprising: (a) an ion source for producing ions from a sample substance; (b) a vacuum region, said vacuum region comprising at least two vacuum stages (183, 184, 185, 186), each of said vacuum stages (183, 184, 185, 186) having means for pumping away gas to produce a partial vacuum, said vacuum stages (183, 184, 185, 186) being in communication with each other such that said ions can move through a sequence of said vacuum stages (183, 184, 185, 186); (c) a Time-of-Flight mass analyzer (192) having a detector, said Time-of-Flight mass analyzer (192) being located in at least one (186) of said vacuum stages (183, 184, 185, 186); (d) at least one multipole ion guide (180, 181) located in said vacuum region; and (e) means for applying electrical voltages to said at least one multipole ion guide; characterized in that: said Time-of-Flight mass analyzer (192) comprises a pulsing region (191).