Quadrupole mass filters with added hexapole fields.

Conventional mass anal. was studied exptl. with 6 quadrupole mass filters with added hexapole fields; 3 with added hexapole fields of 4%, 8% and 12% with equal diam. rods, and 3 with added hexapole fields of 4%, 8% and 12% with unequal diam. rods to remove an added octopole field. Compared with conventional quadrupoles, these rod sets have very large field distortions. With the pos. resolving d.c. applied to the y rods (Mathieu parameter ax.ltbbrac.0) only low resoln. (10-100) and low transmission are seen. With the polarity reversed (αx.rtbbrac.0) much higher resoln. (>=1000) and transmission are possible. Increasing the magnitude of the added hexapole field decreases the limiting resoln. at m/z 609. Removing the added octopole field increases the limiting resoln. In some cases structure is formed on the peaks. For a given scan line slope, U/Vrf, the resoln. decreases as the amplitude of the added hexapole field increases. These results are consistent with changes to the stability diagrams, calcd. here. With ax.rtbbrac.0, adding a hexapole field causes the x stability boundary to move outward with all rod sets. With ax.rtbbrac.0, the boundaries become diffuse and the tip of the stability diagram becomes rounded, limiting the resoln. to \~{}10-100. Where comparisons are possible, expts. show the rod sets with added hexapole fields have transmission 10-300 times less than a conventional quadrupole. Thus these quadrupoles are less useful for mass anal. than conventional quadrupoles. However, it is surprising, given the highly distorted fields, that some of the quadrupoles give resoln. of >=1000. [on SciFinder(R)]