Mass spectrometer arranged to perform MS/MS/MS

#The present invention relates to a mass spectrometer and a method of mass spectrometry. The preferred embodiment relates to a method of performing MS3 or MS/MS/MS.

#Mass isolation was performed in a linear ion trap (“LIT”) by Beaugrand et al. and was presented at ASMS 1988 (ASMS 1988 abstracts page 811).

#Further work was published by Watson et al. in 1989 (“A technique for mass selective ion rejection in a quadrupole reaction chamber”, Int. J. Mass Spec. Ion Proc. 93, 225-235 (1989)). In this article an arrangement was disclosed comprising a penta-quad instrument comprising an EI/CI ion source, a mass selective quadrupole Q1, a first collision cell C1 comprising an RF-only quadrupole, a second mass selective quadrupole Q2, a second collision cell C2 comprising two RF-only quadrupoles, a third mass selective quadrupole Q3 and an electron multiplier detector. The first collision cell C1 was maintained at a pressure of 1×10−3 after the first resolving quadrupole Q1 was used to trap and then selectively eject ions by the application of a dipolar excitation. The isolated ions thus remaining were then released and mass analysed in one of two further resolving quadrupoles. It was suggested that the same auxiliary RF excitation could be used to increase the kinetic energy of the ions so as to induce fragmentation via collision induced dissociation (“CID”).

#Various embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

#FIG. 1 shows a schematic drawing of a mass spectrometer according to a preferred embodiment of the present invention wherein ions are isolated and fragmented one or more times in an ion trap and the resulting fragment ions are then transferred to a fragmentation device arranged downstream of the ion trap and which is arranged to perform a final fragmentation step;

#FIG. 2 shows a flow diagram illustrating an example experiment which may be performed according to an embodiment of the present invention;

#A preferred embodiment of the present invention will now be described with reference to FIG. 1. According to the preferred embodiment a mass spectrometer is provided comprising an ion trap 1 and a separate fragmentation device 2 which is preferably arranged downstream of the on trap 1. The mass spectrometer preferably further comprises a mass analyser 3 which is preferably arranged downstream of the fragmentation device 2.

#FIG. 2 shows the steps which may be performed according to an embodiment of the present invention. Ions are preferably initially accumulated within the ion trap 1 during a first step 4. Once ions have been allowed to accumulate for a predetermined period of time within the ion trap 1, precursor or parent ions of interest are then preferably isolated within the ion trap 1 as a second step 5.

#According to an embodiment the on trap 1 may comprise either a linear or 2D ion trap or a Paul or 3D ion trap. Various methods of isolating ions within the ion trap 1 may be performed including those methods of ion isolation which are disclosed, for example, in U.S. Pat. No. 4,749,860, U.S. Pat. No. 4,882,484 and U.S. Pat. No. 5,134,286 (the teachings of which are incorporated herein by reference).