Patent ID: 8168944

Claim:
A method of processing ions in a linear ion trap, the method comprising a linear ion trap comprising a first pair of rods, a second pair of rods and four auxiliary electrodes interposed between the first pair of rods and the second pair of rods, establishing and maintaining the field comprises providing i) a first RF voltage to the first pair of rods at a first frequency and in a first phase, ii) a second RF voltage to the second pair of rods at a second frequency equal to the first frequency and in a second phase, opposite to the first phase, and iii) an auxiliary RF voltage to the four auxiliary electrodes at an auxiliary frequency equal to the first frequency and substantially in the first phase, iv) a DC voltage to the four auxiliary electrodes; a) establishing and maintaining a two-dimensional substantially quadrupole field in a linear ion trap comprising a first pair of rods, a second pair of rods and four auxiliary electrodes interposed between the first pair of rods and the second pair of rods, the field comprising a quadrupole harmonic of amplitude A2 and an octopole harmonic of amplitude A4, wherein A4 is greater than 0.01% of A2, A4 is less than 5% of A2, and, for any other higher order harmonic with amplitude An present in the field, n being any integer greater than 2 except 4, A4 is greater than ten times An, wherein establishing and maintaining the field comprises providing i) a first RF voltage to the first pair of rods at a first frequency and in a first phase, ii) a second RF voltage to the second pair of rods at a second frequency equal to the first frequency and in a second phase, opposite to the first phase, iii) an auxiliary RF voltage to the four auxiliary electrodes at an auxiliary frequency equal to the first frequency and substantially in the first phase, and iv) a DC voltage to the four auxiliary electrodes; and, b) introducing ions to the field.