Page 241 - Vogel's TEXTBOOK OF QUANTITATIVE CHEMICAL ANALYSIS

OETERMINATION OF ANIONS USINC ION CHROMATOCRAPHV 7.15

prepare a series of standard solutions containing 1.0-5.0 pg of copper per mL,
each solution being 90 per cent with respect to acetone.
Sample solution. Prepare a sample solution containing 100 pg of copper(I1)
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 fil1
a 1.0cm 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(I1) ions with
30mL of 2M nitric acid, place the eluate in a small conical flask (100mL,
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(I1) solutions.
Note. Al1 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.
7.15 DETERMINATION OF ANIONS USlNG ION CHROMATOGRAPHY
The experiment described illustrates the application of ion chromatography
(Section 7.4) to the separation and determination of the following anions: Br-,
Cl -, NO; and NO;. It may be readily extended to include other anions, such
as F-, H, P04, and SOZ-. The experiment is based on the Waters ILC Series
Ion/Liquid Chromatograph which does not require the use of a suppressor
column.
Solutions. Weigh out accurately the following amounts of analytical-grade salts:
NaCl (0.1648 g); KBr (0.1489 g); NaNO, (0.1372 g); NaNO, (0.1 500 g). Dissolve
each salt in 100mL of distilled, de-ionised water in a graduated flask to give
standard concentrates containing 1000 ppm of anion. Store these standard
solutions in clean plastic ware (e.g. polyethylene or polypropylene); glass
containers are not suitable for ion chromatography since cations tend to be
leached from them.
Prepare a series of standard solutions of each anion covering the required
concentration range by appropriate dilution of the standard concentrates with
distilled, de-ionised water.
Borate-gluconate eluant. Prepare a buffer concentrate by dissolving the
following substances in water and making up to 1 L with distilled, de-ionised
water:
Sodium gluconate 16 g
Boric acid 18g
Sodium tetraborate (Na2B,0,, 10H20) 25 g
Glycerol 125 mL
The concentrate is stable for up to six months.