Determination of anions using ion chromatography

Sample solution. Prepare a sample solution containing 100 pg of copper(II) in 1 L of 0.5M sodium chloride solution in a graduated flask. 

Ion exchange column. Prepare the Chelex-100 resin (100- 500 mesh) by digesting it with excess (about 2-3 bed-volumes) of 2M nitric acid at room temperature. Repeat this process twice and then transfer sufficient resin to fill a 1.0 cm diameter column to a depth of 8 cm. Wash the resin column with several bed-volumes of de-ionised water. 

Procedure. Allow the whole of the sample solution (1 L) to flow through the resin column at a rate not exceeding 5 mL min . Wash the column with 250 mL of de-ionised water and reject the washings. Elute the copper(II) ions with 30 mL of 2M nitric acid, place the eluate in a small conical flask (lOOmL, preferably silica) and evaporate carefully to dryness on a hotplate (use a low temperature setting). Dissolve the residue in 1 mL of 0.1 M nitric acid introduced by pipette and then add 9 mL of acetone. Determine copper in the resulting solution using an atomic absorption spectrophotometer which has been calibrated using the standard copper(II) solutions. 

All glass and silica apparatus to be used should be allowed to stand overnight filled with a 1 1 mixture of concentrated nitric and sulphuric acids and then thoroughly rinsed with de-ionised water. This treatment effectively removes traces of metal ions. 

The experiment described illustrates the application of ion chromatography (Section 7.4) to the separation and determination of the following anions Br , Cl , NO3 and N02 It may be readily extended to include other anions, such as F , H2PC 4, and SO -. The experiment is based on the Waters ILC Series Ion/Liquid Chromatograph which does not require the use of a suppressor column. 

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