Ion Chromatography - The Separation of Anions 1



The Separation of Anions


A typical anion exchange column is the Phenomenex Star IC Anion Column that has a wide field of application in industrial water analysis such as wastewater, drinking water, boiler water, condenser water, river water etc. The column packing consists of polystyrene/divinybenzene copolymer carrying quaternary ammonium groups bonded to the polymer packed in a column 10 cm long and 4.6 mm in diameter The column can only tolerate pressures up to 1000 p.s.i. but is used with a suppressor column if it is to be employed with an electrical conductivity detector. The column does not tolerate organic solvents but is stable over a pH range from 1.0 to 12.0. (Metrohm Bulletin No 262/1e)

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Figure 33 A Chromatogram of Anion Standards Separated on an Ion Exchange Resin.


A suitable mobile phase would be an aqueous solution of 1.8mMol/L of sodium carbonate, 1.7mMol/L sodium bicarbonate and operated at 1.5ml/min,. Under these conditions a chromatogram depicting the separation of a set of anion standards is shown in figure 33. It is seen that the system gives a very clean separation of the standards. The column can be regenerated by washing the column for 30min at a flow rate of I ml/min with a solution similar to the recommended mobile phase but with the salts at ten times the concentration.


A practical example of an application of the system to the analysis of drinking water is shown in figure 34. Experimentally the conditions were exactly the same as those used in figure 33 electrical conductivity being employed with suppression. The sample volume of drinking water was 20ml.


(Metrohm Application Bulletin No 262/1 e)

Figure 34. A Chromatogram of Drinking Water Showing the Presence of Fluoride, Chloride, Nitrate and Sulphate.