Question

On page $259$a qualitative discussion described how a positive ion would behave in the xz plane (positive dc potential plane) of a quadrupole mass filter. Construct a similar argument for the behavior of positive ions in the yz plane (negative dc potential plane).

Short answer

Positive ions migrate toward the rod when a negative dc voltage is present in the yz plane, where they are stopped.

Step-by-step solution

Concept Introduction

A quadrupole is a set of configurations of things like electric charge or current, or gravitational mass that can exist in ideal form, but it's usually just part of a multipole expansion of a more intricate structure that represents various orders of complexity.

Concept Explained

The positive ion in xz plane under positive dc potential is described as follow:

Positive ions migrate toward the rods when a negative dc voltage is present in the yz plane, where they are stopped. In the other scenario, when an additional ac voltage is present, this movement is hindered during the positive part of the cycle, with the lighter ions being more affected than the heavier ones.

Thus, the yz plane act as the low-pass filter removing heavier ions.