Mass Analysis with Islands of Stability with Linear Quadrupoles Incorporating Higher Order Multipole Fields.

Mass anal. with islands of stability was studied with three linear quadrupole mass filters: two with 4% added hexapole fields constructed with equal diam. (quadrupole 4A) and unequal diam. (quadrupole 4B) rods, and a conventional round-rod quadrupole that has apparently been slightly damaged. Islands are formed by applying auxiliary quadrupole excitation. With the Mathieu parameter, a < 0, mass anal. with both quadrupoles with hexapole fields operated normally, i.e., without islands, gives only low resoln. A factor of >=10 increase in resoln. is possible using stability islands. With a > 0, when quadrupole 4A is operated normally, peak shapes similar to that of a conventional quadrupole can be obtained at resolns. >850. At lower resolns., peaks are split. When quadrupole 4B is operated without islands, resoln. up to 2000 is possible, but there are low mass tails and structure is formed on the peaks. With mass anal. with an island of stability, both quadrupoles 4A and 4B show peaks free of structure and without tails. Ion transmission is also improved with some operating conditions. With the conventional round-rod quadrupole, mass anal. with islands of stability increases the limiting resoln. from 2500 to 4360. At a resoln. of 2500, the transmission is increased by about two orders of magnitude. The use of islands of stability improves mass anal. with quadrupoles with distorted fields, and may, in the future, allow use of quadrupoles constructed with at least some lower mech. tolerances. [on SciFinder(R)]