Anions in wastewaters - Determination of Anions in Natural and Treated Waters - page 552

0.80mg L −1 ) and Ni(CN) 4

2− (CN − , 0.96mg L −1 ) were 1.1%, 1.5% and 0.5%,

respectively.
Lui et al. [63] have described an automated system for determination of total and labile
cyanide in water samples. The stable metal-cyanide complexes such as Fe(CN) 6 3− are
photo-dissociated in an acidic medium with an on-line Pyrex glass reaction coil irradiated
by an intense mercury lamp. The released cyanide is separated from most interferences in
the sample matrix and is collected in a dilute sodium hydroxide solution by gas diffusion
using a hydrophobic porous membrane separator. The cyanide ion is then separated from
remaining interferences such as sulphide by ion exchange chromatography and is
detected by an amperometric detector. The characteristics of the automated system were
studied with solutions of free cyanide and metal-cyanide complexes. The results of
cyanide determination for a number of wastewater samples obtained with this method
were compared with those obtained with the standard method. The sample throughput of
the system is eight samples per h and the detection limit for total cyanide is 0.1µg L −1 .

8.11 Ethylene diamine tetraacetate

8.11.1 Liquid chromatography
Dai and Helz [64] carried out a liquid chromatographic determination of ethylene
diaminetetraacetate using an amperometric detector. Down to 0.15mg L −1 of this anion

can be determined in waste water.

8.12 Fluoride

8.12.1 Microdiffusion method
Microdifusion has been applied [65] to the determination of down to 50µg L −1 fluoride in
waste waters, effluents and river waters. The sample (1ml containing <25µg of fluoride
ion) is placed in the outer compartment of a polypropylene Conway-type diffusion cell
containing 1ml of 0.5N sodium hydroxide in a polystyrene cup in the inner compartment,
then 1ml of 70 vol% sulphuric acid is rapidly added to the sample and a polystyrene lid,
greased with silicone, is placed on the cell, which is then heated in an oven at 65°C for
5h. To the dried residue in the centre cup is added 1 drop of phenolphthalein solution and
the contents are washed with water into a volumetric flask. Fluoride is then determined
by the lanthanum complexan or spectrophotometric procedure [66,67],

8.12.2 Ion chromatography
The application of this technique is discussed under multianion analysis in sections 12.7.1
and 12.7.2.