Instant Notes: Analytical Chemistry

Section E – Spectrometric techniques

E5 INDUCTIVELY COUPLED

PLASMA SPECTROMETRY

Principles When heated to temperatures above 6000 K, gases such as argon form a plasma

• that is a gas containing a high proportion of electrons and ions. The plasma
  may be produced by a DC arc discharge or by inductive heating in an induc-
  tively coupled plasma (ICP) torch.
  Discharge of a high voltage from a Tesla coil through flowing argon will
  provide free electrons which will ‘ignite’ the gas to a plasma. If the conducting
  plasma is enclosed in a high frequency electromagnetic field, then it will accel-
  erate the ions and electrons and cause collisions with the support gas, argon,
  and the analyte. The temperature rises to around 10 000 K. At such tempera-
  tures, energy transfer is efficient and the plasma becomes self-sustaining. It is
  held in place by the magnetic field in the form of a fireball. The sample aerosol
  enters the fireball at high speed and is pushed through it, becoming heated and
  emerging as a plume, which contains the sample elements as atoms or ions, free
  of molecular association. As they cool to around 6000-7000 K, they relax to their
  ground state and emit their characteristic spectral lines. This technique is known
  as ICP-atomic emission spectrometry (ICP-AES) or sometimes as ICP-optical

E6 X-ray emission spectrometry

If part of the plume is diverted into a mass spectrometer, the isotopic masses

Key Notes

A gas plasma provides a very high temperature excitation source for

atomic spectrometry. Quantitative analysis for a large number of

elements may be achieved rapidly. By combination with a mass

spectrometer, individual isotopes may be identified and quantified.

A high-voltage discharge into an argon flow creates a plasma, which is

sustained by induction heating due to the field of a radiofrequency coil.

The sample solution is nebulized into the plasma. The emitted radiation

is analyzed using a monochromator and photomultiplier detector.

If part of the sample stream from the plasma is directed into a mass

spectrometer, the resulting mass spectrum is used to analyze for elements

and to determine isotopic ratios.

Over 70 elements may be determined using these techniques, many down

to ultra-trace levels.

Related topics Flame atomic emission Mass spectrometry (E14)

spectrometry (E4)

E7 Atomic absorption and atomic fluorescence spectrometry

fluorescence spectrometry (E7)

Principles

Inductively coupled

plasmas

Applications

Inductively coupled

plasma-mass

spectrometry