Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 162

are injected into an on-line cupric sulphide packed column, and potassium hydroxide
solution (pH 11.0) is used as the carrier. The eluent containing the analyte as
cuprocyanide complexes is introduced into the nebuliser of the atomic absorption
spectrometer. This novel flow injection analysis/atomic absorption spectrometric method
has a sensitivity of 1mg L −1 cyanide for 0.0044A and a detection limit also of 1mg L −1
cyanide. The precision of the technique is better than 2% relative standard deviation at
26ppm cyanide with a sampling rate of 40-50 samples/h. The effects of flow rate, sample
volume, and anionic interference on the flow injection analysis/atomic absorption
spectrometric signals are discussed. Only citrates were found to interfere significantly
(+5% at 20-fold concentration). The conversion method is potentially applicable to other
anions.
2.23.5 Flow injection analysis
Fogg and Alonso [270] have described an oxidative amperometric flow injection method
for the determination of cyanide at an electrochemically pretreated glass carbon
electrode.
The application of this technique is also discussed under multianion analysis in section
14.4.1.4.
2.23.6 Potentiometric method
A method based on microdiffusion coupled with potentiometric measurement has been
used to determine cyanide in non saline waters [271].
2.23.7 Ion selective electrodes
Ion selective potentiometry in alkaline solution provides a suitable finish for the
determination of cyanide [272-277]. Sulphide ion is an interferent, and a cadmium nitrate
treatment has been found to remove sulphide without influencing the response of the
silver iodide-silver sulphide electrode. If both the precipitate and solution from this
treatment are colourless (sulphide absent), filtration of the mixture before the
potentiometric measurement is unnecessary. Since the electrode response of the electrode
is pH dependent, standards and samples must be brought to the same pH. It is noteworthy
that the silver-silver sulphide electrode (eg Orion 94-16) is more sensitive to cyanide
than the silver iodide-silver sulphide one [272,274] but the response is affected by
cadmium ion.
2.23.8 Infrared spectroscopy
Stuart et al. [278] used infrared spectroscopy in speciation studies of cyanide in non
saline waters. These workers applied the method to the determination of 10-100mg L −1
cyanide in non saline waters.