Anions in wastewaters - Determination of Anions in Natural and Treated Waters - page 537

14.2.3.2.
8.8.3 Flow injection analysis
Zhu and Fang [33] used an automated flow-injection system with gas-diffusion
separation and preconcentration, coupled with spectrophotometric detection, to determine
cyanide in wastewaters. An unstable red intermediate product of the reaction of cyanide
with isonicotinic acid 3-methyl-1-phenyl-2-pyrozolin-5-one is measured in the
determination. The sampling frequency was 40 samples/h and the detection limit was
0.6µg L −1 with a 2mL sample; the relative standard deviation was 1.4% (n =22) at the
0.5mg L −1 level
8.8.4 Atomic absorption spectrometry
Rosentreter and Skogerboe [34] have used this technique to study the trace determination
of speciation of free cyanide in wastewaters.
By utilising a high selective reaction between silver metal and cyanide ions, these
workers developed an apparatus and procedure for the analytical determination of
aqueous cyanide species. The rapid analysis of free cyanide was achieved through the use
of pure silver filters as the reaction medium and atomic absorption spectroscopy as the
detection method. This methodology has allowed for the quantitative detection of cyanide
ions down to the sub-parts-per-billion level. By incorporating selective oxidation, kinetic
equilibria, and photo-dissociation techniques, the silver-cyanide reaction technique has
been adapted to provide a means of categorically speciating aqueous cyanide compounds.
The complete system has been shown to be free from common chemical interferences,
including thiocyanate. This detection system provides high-speed cyanide determinations
with little to no sample preparation or instrument supervision.
8.8.5 Chronopotentiometry
Procopio et al. [35] carried out an indirect determination of cyanide in waste waters by
this technique. Cyanide was determined by measuring the displacement of the quarter
wave potential of the chronopotentiometric graph of formaldehyde. After separation of
the cyanide by distillation into alkaline media, formaldehyde solution was added and the
resultant solution transferred to the cell of a constant current coulostat. A constant
potential of −1.4V was applied for 5min while nitrogen flowed through continuously.
The potential was removed and the solution allowed to become quiescent, before
applying a constant current to the working gold electrode. A transition time of 30s was
obtained. From the displacement of the formaldehyde curve with and without cyanide
present, a detection limit of 10µg L −1 cyanide was obtained with a relative error of less
than 2% and a relative standard deviation of 1%.
8.8.6 Ion selective electrodes
Ion selective potentiometry in alkaline solution provides a suitable finish for the