the invention fig4 illustrates a modification of fig3 in which the first ion guide segment 48 in fig3 is oriented coaxial with capillary 10 axis 36 and extends not only through the vacuum partition 42 between the first vacuum pumping stage 2 and the second vacuum pumping stage 3 but also extends through an additional vacuum partition 56 compared to the embodiment of fig3 that divides the vacuum pumping stage 3 of fig3 into an additional vacuum pumping stage which is shown in fig4 as vacuum pumping stage 55 ion guide segment 58 exit end 59 is positioned in the third vacuum pumping stage 55 in fig4 the second ion guide segment 52 is then oriented at an angle 38 with respect to the axis 36 and the configuration of this embodiment is the same as in fig3 downstream of the gap 51 the advantage of the embodiment shown in fig4 relative to the embodiment of fig3 is that ions that enter the first ion guide segment 58 along axis 38 may proceed along ion guide segment 58 and experience collisional cooling of ion kinetic energy before their beam direction is re directed from the capillary 10 axis 36 to the ion guide segment 52 axis 26 cooling the ion 39 s kinetic energy improves the efficiency with which the rf fields within an ion guide are able to re direct the ions 39 beam path because the effectiveness of a particular rf field strength for guiding or re directing ions decreases as the kinetic energy of the ions increases hence allowing the ions 39 kinetic energy.