Page 131 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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5
Inductively Coupled Plasma Mass Spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) is the marriage of two well established
techniques, namely the inductively coupled plasma and mass spectrometry. The ICP has been
described as an ideal ion source for inorganic mass spectrometry. The high temperature of the ICP
ensures almost complete decomposition of the sample into its constituent atoms, and the ionization
conditions within the ICP result in highly efficient ionization of most elements in the Periodic Table
and, importantly, these ions are almost exclusively singly charged.

A schematic diagram of an ICP-MS instrument is shown in Fig. 5.1. The 'ICP part' bears an almost
exact resemblance to the ICP used for atomic emission spectrometry, with the obvious exception that it
is turned on one side. Indeed, sample introduction systems, radiofrequency generators and the nature of
ICP itself are often the same for ICP-MS and ICP-AES systems, with the usual variations between
individual manufacturers.

5.1 Sample Introduction

The sample is introduced into the ICP as a liquid which must usually contain less than 0.1% dissolved
solids to prevent salt build-up on the nickel cones (see Section 5.3). This is in contrast to ICP-AES,
which can tolerate up to 1% dissolved solids. The sample is converted to an aerosol by means of a
pneumatic nebulizer, and the droplets pass through a spray chamber, into the injector tube of the
quartz torch and thence into the central channel of the ICP. These processes are identical with those
described for ICP-AES (see Section 4.4.3), and the different types of