Browse Prior Art Database

Injection and Extraction of Ions in Monopole Mass Spectrometer

IP.com Disclosure Number: IPCOM000094880D
Original Publication Date: 1965-Jun-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 3 page(s) / 36K

Publishing Venue

IBM

Related People

Lever, RF: AUTHOR

Abstract

Ions are injected into V-shaped electrode 10 of a monopole mass spectrometer at an oblique angle through injection tube 12. End effects are eliminated and excellent focusing of ions is obtained at extraction tube 14.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 3

Injection and Extraction of Ions in Monopole Mass Spectrometer

Ions are injected into V-shaped electrode 10 of a monopole mass spectrometer at an oblique angle through injection tube 12. End effects are eliminated and excellent focusing of ions is obtained at extraction tube 14.

As operation of this spectrometer is sensitive to the velocity of injection v of the ions, it is chosen so that the ions remain in the alternating field region of the monopole an integral number of RF cycles, i.e., s/v = 2n pi/omega. In the equation, s is the source-collector distance, v is the component of ion velocity parallel to the z axis, w/2 pi is the frequency of the RF supply, and n is an integer. By choosing appropriate A and O values of Mathieu's equation, discussed, below, exact focusing is obtained with resulting very exact mass discrimination.

With regard to a monopole mass spectrometer, a reference is Review of Scientific Instruments, 34, 1, January 1963. Such apparatus separates ions of different charge to mass ratio by passing them between two electrodes with a potential U + V cos wt applied across them. V-shaped electrode 10 replaces one quadrant of the intersecting ground potential surfaces of the comparable quadrupole mass spectrometer for which the reference is Zeitschrift fur Physik, 152, 143, 1958. Electrode 16 presents a cylindrical surface 18 and the DC potential U plus RF potential V cos wt is applied between electrodes 14 and 16 via terminal 20 and ground. Ion trajectories 22 in the monopole mass spectrometer result from independent x and y vibrations each obeying Mathieu's equation d2x/dE/2/ + (A + 2Q cos 2&) x = 0, d/2/y/d&/2/ - (A + 2Q cos 2&) y = 0, where epsilon = wt/2, A = 8eU/(mw/2/r 2) and Q = 4eV/(mw2 r02). The spatial coordinate z and the quantity E are related via the velocity v, i.e., 2&/ z = w/v.

It is difficult to obtain solutions of this equation analytically and tabulated values exist only for a few A and Q values. However, it is possible to integrate the equation numerically using a computer and to plot automat...