Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES)

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Inductively Coupled Plasma-Optical Emission
Spectrometry (ICP-OES)
Projects using ICP-OES
Calibration
What is ICP-OES?
Inductively Coupled Plasma Optical Emission
Spectrometry (ICP-OES) is a fast, multi-element
technique used to measure trace metals such as
lead (Pb), copper (Cu), nickel (Ni) and zinc (Zn)
and major cations such as calcium (Ca),
magnesium (Mg) and sodium (Na). Inductively
Coupled Plasma techniques operate by decomposing
a liquid sample by intense heat into a cloud of
hot gases with an inductive coupled plasma (a
state of matter containing electrons and ionised
atoms of Argon). The plasma reaches temperatures
of around 10,000C
A calibration is necessary for quantitative
analysis (figure 2). By comparing the intensity
of light emitted by solutions of known metal
concentrations with unknown sample solutions,
metal concentration can be determined.
We use ICP-OES to measure trace metals and major
cations in a range of environmental samples from
urban canals to remote lake sediments. Recent
third year IGS projects have included analysis of
Pb in vegetables grown on heavily polluted urban
soils and analysis of Cu, Zn, Cd and Ni in soils
close to a major road.
Examples of research at QMUL
Miriam Reid and Kate Spencer use ICP-OES to
investigate heavy metal contamination in
estuarine sediments. Toxic metals have been
released by industry and sewage outflow and
deposited in sediments. Figure 3 shows Ni
concentrations in Medway Estuary sediments.
The high temperature causes excitation and
ionisation of the sample atoms. Once the atoms or
ions are in their excited energy states, they can
decay to lower energy states whilst emitting
light of specific wavelengths depending of the
elements in the solution. In OES, the intensity
of the light emitted at specific wavelengths is
measured and used to determine the concentrations
of the elements of interest.
Figure 2. Calibration curve for Cu intensity
measured from standards of 0. 1. 2. 4 and 10 mg
l-1
Advantages and limitations of ICP-OES

• ICP-OES is a moderately sensitive techniques that
  can analyse a wide range of elements
  simultaneously. Under optimum conditions it can
  analyse over 100 samples per day. It is
  important, however, to be aware of the
  limitations of the method. These include
• Spectral interference between different
  elements. The wavelength of one element's
  light emission can sometimes be close enough to
  that of another element to cause problems.
• Matrix effects caused by high concentrations of
  an element in the sample, (most commonly the
  easily ionisable Na, K, Mg or Ca) can change
  the way the sample is introduced to the flame
  or the thermal characteristics of the plasma and
  lead to over or underestimation of sample
  concentration.
• Optimum conditions for analysis occur for
  different elements under different conditions,
  therefore sensitivity can be compromised when
  running for multi-element analysis.

Figure 3. Nickel contamination of sediments in
the Medway Estuary (Miriam Reid).

• Other recent projects include
• Analysis of arsenic and lead contamination in
  soils around a new development for Harrow
  Borough Council.
• Analysis of lake sediment samples from the Peak
  and Lake Districts for Cu, Zn, Cd and Pb in
  collaboration with researchers at York
  University.
• Analysis of base cations in storm flows from
  streams on Exmoor in collaboration with
  researchers from the University of Plymouth.

Figure 1. The Varian Vista-PRO CCD Simultaneous
ICP-OES in the Physical Geography laboratories
References Jose Luis Todol, Luis Gras, Vicente
Hernandis and Juan Mora (2002). Elemental matrix
effects in ICP-AES. J. Anal. At. Spectrom., 17,
142169