Method of mass analyzing a sample by use of a quadrupole ion trap

The method of mass analyzing a sample which comprises the steps of:

• (a) ionizing the sample to form ions indicative of the sample constituents;
• (b) temporarily trapping all of said ions in an ion storage apparatus of the type having two end caps and a ring by applying voltage U+V sin .omega.t across the ring and end caps to provide a substantially quadrupole electric field;
• (c) scanning one or more of U, V and .omega. between predetermined limits so that trapped ions of specific mass become sequentially and selectively unstable and sequentially exit from the ion trap;
• and
• (d) detecting the unstable ions as they exit the ion trap to provide an indication of the ions as a function of U, V and .omega. applied to thereby identify the mass of the ions.

A method of mass analyzing a sample comprising the steps of:

• (a) ionizing the sample to form ions indicative of the sample constituents;
• (b) temporarily trapping all of said ions in a three dimensional quadrupole field;
• (c) improving the mass resolution and sensitivity of said analysis of trapped ion by introduction of collision gas, and
• (d) sequentially selecting by ejecting ion of different mass values by scanning the three dimensional quadrupole field.

A method of mass analyzing a sample which comprises the steps of:

• applying RF and d.c. voltages V+U sin .omega.t between the ring electrode and the end cap electrodes of an ion trap electrode structure to impose in the region interior to said electrode structure a potential distribution approximating a three dimensional quadrupole field which is described in the cartesian coordinate system by the equation ##EQU2## where .PHI.=the electric potential relative to the electric potential at the origin (x=0, y=0, Z=0)
• V'=a magnitude describing RF component of the electric potential field
• .omega.=.pi. f
• f=frequency of radio frequency component of the electric potential field
• V'=a magnitude describing the d.c. component of the electric potential field
• r.sub.o '=characteristic dimension of the potential field and which has ion trapping characteristics defined by the parameters S.sub.a and S.sub.q where ##EQU3## introducing ions into all three dimensional quadrupole field region and trapping said ions having masses of interest;
• changing S.sub.q so that the range of ion specific masses (m/e) stable in the field changes causing trapped ions to become unstable and exit the trapping field in sequence of said ions specific masses (m/e);
• detecting the unstable ions;
• and
• providing a signal indicative of the m/e ratio as the ions become unstable.