Patent ID: 6891153

Claim:
A mass spectrometer comprising: an ion source for producing ions; an input vacuum chamber comprising at least one AC ion guide for transmitting said ions, said AC ion guide comprising a plurality of electrodes having apertures, said apertures being aligned so that ions travel through them as they are transmitted by said ion guide; an analyzer vacuum chamber comprising an ion mass analyzer disposed to receive ions after they have been transmitted by said ion guide; at least one differential pumping apertured electrode though which ions may pass, said at least one differential pumping apertured electrode being disposed between said input vacuum chamber and said analyzer vacuum chamber to permit said analyzer vacuum chamber to be maintained at a lower pressure than said input vacuum chamber; at least one alternating current (AC) generator connected to an input chamber reference potential for providing AC potentials to said plurality of electrodes; wherein: at least 90% of said apertures are substantially the same size; at least 90% of said plurality of electrodes forming said AC ion guide are connected to said AC generator in such a way that at any instant during an AC cycle of the output of said AC generator, adjacent ones of said electrodes are supplied respectively with approximately equal positive and negative potentials relative to said input chamber reference potential; and wherein said input vacuum chamber is arranged to be maintained at a pressure selected from the group consisting of: (i) ≧0.1 mbar; (ii) ≧0.5 mbar; (iii) ≧0.7 mbar; (iv) ≧1.0 mbar; (v) ≧1.3 mbar; (vi) ≧1.5 mbar; (vii) ≧2.0 mbar; (viii) ≧2.5 mbar; (ix) ≧3.0 mbar; (x) ≧3.5 mbar; (xi) ≧4.0 mbar; (xii) ≧4.5 mbar; (xiii) ≧5.0 mbar; (xiv) ≧6.0 mbar; (xv) ≧7.0 mbar; (xvi) ≧8.0 mbar; (xvii) ≧9.0 mbar; (xviii) ≧10.0 mbar; (xix) 1-5 mbar; (xx) 1-2 mbar; (xxi) 0.5-1.5 mbar.