6.13: Inductively Coupled Plasma–Mass Spectrometry (ICP–MS): Overview
In inductively coupled plasma–mass spectrometry (ICP–MS), an inductively coupled plasma (ICP) torch is used as an atomizer and ionizer. Solid samples are dissolved and volatilized before being introduced into the high-temperature argon plasma, while solution samples are nebulized and passed through the high-temperature argon plasma. Plasma dissociates the analytes and ionizes their component atoms to form a mixture of positive ions and molecular species. The positive ions are then passed on to the mass spectrometer and analyzed by their m/z values. Since an ICP source operates at atmospheric pressure and a mass spectrometer requires a vacuum, the plasma is passed through an interfacial region, reducing the pressure from 1 bar to around 10−9 bar. The interfacial region consists of two metallic cones (a sampler cone and a skimmer cone), an extraction lens, and a collision cell. The sampler cone and skimmer cone have narrow orifices allowing only a small amount of plasma to pass through. The high negative voltage of the extraction lens allows only the positive ions to enter the collision cell. The collision cell reduces the range of kinetic energies of the ions and directs the ion beam into the quadrupole mass analyzer. ICP–MS is a useful technique in elemental analysis due to its low detection limits, high selectivity, and excellent sensitivity.
