National Physical Laboratory

Ion Chromatography

Ion chromatography is used in the trace analysis area primarily to determine the anionic and cationic composition of ambient particulate matter (PM).  In particular, measurements of nitrate, sulphate and chloride are of importance.

The table below shows what compounds these anions can exist as part of within ambient particulate matter.

Ion Compound Source
SO42- (NH4)2SO4 Atmospheric SO2 (from fuel combustion) oxidises and reacts with NH3
Cl- NaCl Sea salt
NO3- NH4NO3
NaNO3
Atmospheric NOx (from fuel combustion) oxidises and reacts with NH3 (from agricultural waste) or Na

Exposure to particulate matter can cause or exacerbate respiratory and cardiovascular diseases. It is important to determine the composition of PM so that the sources can be identified and source emissions regulated. The anionic species within ambient particulates across the UK are measured within the UK Department for Environment, Food and Rural Affairs’ Particles Network, which is currently managed by NPL.

When observed under an electron microscope, the individual particles within the PM can easily be seen, as shown in the Figure below.

Particulate Matter Filter
A filter loaded with ambient particulate matter (left)
and enlarged under and electron microscope (right)
where the fibres of the filter and individual particles are visible

The chloride, nitrate and sulphate ions can be extracted from the filter by sonication in a solution of sodium carbonate and sodium hydrogen carbonate. This extract can then be subsequently analysed by anion-exchange ion chromatography.  A typical ion chromatogram for the measurement of chloride, nitrate and sulphate in PM, is shown in the Figure below.

Chromatogram
A typical chromatogram showing, from left to right, chloride, nitrate and sulphate peaks 

References

  • Brown, R J C, Yardley, R E, Brown, A S, Edwards, P R, Rivier, C, Yardin, C “Analytical methodologies with very low blank levels: implications for practical and empirical evaluations of the limit of detection.” Analytical Letters, 2006, 39, (6), 1229-1241
  • Brown, R J C, Edwards, P R “The effect of the physical matrix on accurate measurements using fixed volume analytical techniques.” Journal of Separation Science, 2006, 29, (13), 2072-2077
Last Updated: 3 Feb 2012
Created: 2 Aug 2007

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