Multianion analysis, applications of ion chromatography - Determination of Anions in Natural and Treated Waters - page 692

determined as total free cyanide while nickel and copper complexes can only partially be
determined in this way. The strongly bound cyanide in gold, iron or cobalt complexes
cannot be determined by this method.
This method is based on the work of Pihiar and Kosta [19,20] who showed that a silver
working electrode has the ability to produce a current that is linearly proportional to the
concentration of cyanide in an amperometric electrochemical flow through cell. The
reaction for cyanide is

Under these conditions sulphides and halides produce insoluble precipitates rather than
soluble complexes:

Rocklin and Johnson [23] overcame the latter problem by placing an ion exchange
column in front of the electrochemical detector. Cyanide and sulphide are separated and
are thus determined simultaneously Although bromide and iodide can be determined by
ion chromatography with conductivity detection, the use of electrochemical detection
results in greater selectivity as well as increased sensitivity.

Reagents
Cyanide standard solution. Prepare from a 1000mg L −1 sodium cyanide stock solution,
standardised by argentometric titration.
S ulphide standards. Prepare by diluting 21% (NH 4 ) 2 S ammonium sulphide. K 3 Fe(CN)

6 .

N i(CN) 4 2− . Prepare from sodium cyanide and nickel acetate.
C d(CN) 4 2− . Prepare from 1000mg L −1 solutions of cadmium chloride and sodium
cyanide.
Copper cyanide solutions. Prepare by adding stoichiometric quantities of sodium
cyanide to a 1.0×10 −5 mol L −1 cuprous cyanide solution.

Apparatus
Dionex System 2010 (P/B 352OL) ion chromatograph with sample loop size 50µL and
eluent flow 2.5ml min −1 Cyanide and sulphide separated on an HPIC-AS3 (P/N 35311)
anion exchange column using an eluent consisting of 14.7mmol L −1 ethylenediamine,
10mmol L −1 NaH 2 BO 3 (prepared from H 3 BO 3 and NaOH) and 1.0mmol L −1 sodium
carbonate. The eluent pH is 11.0. Chromatography of iodide was performed by using an
HPIC-ASI (P/N 30827) column with an eluent consisting of 2mol L −1 sodium nitrate.
Chromatography of bromide was performed using an HPIC-AS3 (P/N 30985) column
with an eluent consisting of 2mmol L −1 sodium carbonate.
Electrochemical detection performed with an Ion Chrom/Amperometric Detector (P/N
35221). The cell (Fig. 12.37) consists of a silver rod working electrode 1.3cm
long×0.178cm in diameter, an Ag/AgCl reference electrode separated from the flowing