Anions in wastewaters - Determination of Anions in Natural and Treated Waters - page 546

complex metal cyanides to both deionised water solutions and wastewater samples
containing or spiked with nitrate and thiocyanate. The recovery of cyanide was virtually
complete.
For the cyanide complexes of chromium, copper, iron, and nickel, the recovery of
cyanide was usually greater than 95%. As mentioned previously, the failure to disrupt
hexacyanocobaltate(III) due to its kinetic inertness, is a limitation of most total cyanide
procedures.
Leschber and Schlichting [55] discussed the decomposability of complex metal
cyanides in the determination of cyanide in waste water. These workers found that
complex cyanides of zinc, cadmium, copper, nickel, iron(II) and iron(III) corresponding
to 1-100mg L −1 cyanide are easily decomposed by distilling the sample in the presence
of dilute sulphuric acid and total cyanide can be determined in the distillate. However, K 3
(Co(CN) 6 ) (hexacyano cobalt(III)) is only partially decomposed by this treatment.
Drikas and Routley [56] have described a spectrophotometric method for the
determination of total cyanide in waste water samples.

8.9.2 Flow injection analysis
Zhu and Fang [33] have described a spectrophotometric determination of total cyanide in
waste waters in a flow injection system with a gas diffusion separation. The method is
based on the formation of the unstable red intermediate product of the reaction of cyanide
with isonicotinic acid and pyrazolone. A detection limit of 0.6µg L −1 was achieved.

Cobalt interfered in this method.

8.9.3 Atomic absorption spectroscopy
Rameyer and Janauer [57] have described a method using reactive ion exchange for the
determination of complex iron cyanides in water in the mg L −1 range. The cyanide
complexes are preconcentrated on shallow beds of sulphonated cation-exchange resin in
the copper(II) form by precipitation as copper hexacyanoferrate(II) or copper
hexacyanoferrate(III). Other cations, including contaminant iron species, are eluted with
hydrochloric acid. Aqueous ammonia relatively releases and elutes the hexacyanoferrate
by the formation of the copper amine complex. Finally the complex cyanides are
determined as iron by atomic absorption spectrometry.

8.9.4 Ion selective electrodes
A procedure has been developed for determination of cyanide [58] in concentrations
down to 2mg L −1 by manual or automated potentiometry using a cyanide ion selective
electrode. Distinction is made between simple and complex cyanides by irradiation with
ultraviolet light.
Csikai and Barnard [54] used EDTA at pH 4 to displace cyanide from metal complexes
and to avoid converting thiocyanate to free cyanide from metal where oxidants are
present. Sulphamic acid is added to prevent nitrite interference, sulphides are removed
from the sample with calcium carbonate and from distillates with cadmium nitrate.