Question

Why does the negative potential superimposed with an AC current allow Low mass particles to pass through the quadrupole ? Explain in great detail with a figure or two.

Please don't copy and paste the old answer. I've already asked this question and the answer was incorrect

Answer 1

A quadupole system consists of four rods that are arranged in an equal distance from each other in a parallel manner. Ions are accelerated by a negative voltage plate before they enter the quadrupole and travel down the centre of the rods (in the z-direction).For now, imagine that only AC current potential si applied to the rods.

Half the time when potential was positive, the ions (cations ) would be repelled by the rods charge and consequently move towards the centre of the rods. Likewise when potential will negative, ions would accelerate towards the rods in response to an attractive force. If during the -ve pot. an ion comes into contact with the rod , it will neutralised and is removed by the vaccum.The mass of the ion is one of the factor that influence whether or not a particle strikes the rod during the negative cycle.

When talking about the low mass particles, it go through the negative quadrupole attractively but when the AC current swithces to postive the low mass means the small particles can shift away quickly enough betterly to where make it through the filter than the bigger ones.