Hardware manual

Technical Information 6

Agilent 7500 Series ICP-MS Hardware Manual 6-11

Ion Lenses - Principles of Operation

There are three ion lens main components: Extraction lens, Einzel lens and

Omega lens.

To understand the mechanism of the ion lens, consider equipotential lines of

an electrical field (Figure 128). When the electrical field is in parallel and at A

volts above the ground level, a positive ion is accelerated as a function of

voltage. The Einzel lens consists of three circular- hole lenses, which create the

electrical field, see Figure 128.

Figure 128 Ion Lens Focusing

The focal point depends on the ion energy. As the energy of a lighter mass ion

is different from that of a heavier mass ion in the ICP- MS, mass

discrimination occurs.

The ion energy is a sum of the potential energy and the kinetic energy. The

plasma and the interface mainly determine the potential energy. When the

plasma is completely coupled with the RF coil inductively, the plasma has only

a slight DC potential and there is little potential difference between the

plasma and the interface, which is at the ground level. However, there is

Ions inside Parallel-plate electrostatic Lens

Examples of Field-effect Ion Lens Used in ICP-MS

Elecrpde

Equipotential Surface

Orbit of Ions

AV 0V

V1 V2

E1 E2

V1 V2 V3