Ion Chromatography

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Ion Chromatography
Projects using ion chromatography
What is ion chromatography
Figure 1 illustrates the process of ion
chromatography. An aqueous solution called a
mobile phase or eluent is used to carry the water
sample into and through a column containing a
positively or negatively charged resin
(stationary phase). The mobile phase is of the
same charge as the ions of interest but is less
efficiently retained on the resin. Initially
therefore the target ions are retained on the
resin whilst the mobile phase continues through
the column. However the target ions can be
displaced by increasing the concentration of the
mobile phase. The ions of interest are then
detected as they leave the column typically by
conductivity or UV/Visible light absorbance.

• Chromatography is the process of separating
  different components from a solution or a gas.
  Chromatographic techniques work by passing the
  solution (or gas) of interest over a stationary
  phase - a substance with which the solution
  interacts. The stationary phase interacts more
  strongly with some components in the solution
  than others. This results in components passing
  through the stationary phase at different rates
  effectively separating them for analysis.
• Ion chromatography is the process of separating
  ions (positively or negatively charged atoms or
  molecules) from a solution using a stationary
  phase that contains oppositely charged ions.
  There are two main types of ion chromatography
• Anion exchange chromatography is commonly used
  in environmental sciences to measure negatively
  charged anions such as nitrate nitrite
  phosphate and sulphate.
• Cation exchange chromatography is commonly
  used to measure positively charged anions such
  as ammonia sodium or potassium.

We use ion chromatography primarily to
investigate water quality. Recent third year IGS
projects have included analysis of nutrient
levels in bathing pools on Hampstead Heath
affected by toxic algae blooms water quality in
Rutland Water Reservoir and the River Mole.
Examples of research at QMUL
Fotis Sgouridis is investigating nutrient fluxes
in a restored floodplain along the River Cole. He
is monitoring ground water concentrations of
anions including chloride sulphate and nitrate
along a transect extending away from the river.
Boreholes at 40 m intervals provide a cross
section of ground water nutrient levels at the
site (figure 3).
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Stage 1. Water sample and eluent are injected
into column
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Stage 2. Anions in the sample interact with
cation exchange resin in the column. The blue
anion interacts more strongly with the column and
passes through relatively slowly.



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Figure 3. Anions in ground water on the restored
floodplain of the River Cole (Fotis Sgouridis).








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• Other recent projects include
• Analysis of nitrate phosphate sulphate
  chloride and fluoride in storm flows from
  streams on Exmoor in collaboration with
  researchers from the University of Plymouth.
• Analysis of nitrate levels in water samples from
  a potentially contaminated village water supply
  in China for More4 News.
• Analysis of sulphate in sediment extracts as
  part of a sequential extraction procedure to
  identify binding sites on estuarine sediments.

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Stage 3. Anions leave the column. At a rate
determined by the chemical properties of the
anions the resin and the eluent
Figure 1. Dionex ICS 2500 Ion Chromatograph in
the Physical Geography laboratories
The Dionex ICS 2500 can be used for both anion
and cation exchange chromatography.
Figure 2. Ion chromatography.