Anions in wastewaters - Determination of Anions in Natural and Treated Waters - page 536

for determining this ion. This method can be used, as described above, for the
determination of free cyanide or, with a suitable sample pretreatment, to the
determination of total cyanide. The pretreatment involves distillation with phosphoric
acid and an alkaline 10% EDTA solution, using 2% sodium hydroxide or 2% sodium
acetate as absorbent. For the sodium hydroxide solution (2%) absorbent, the receiving
solution was neutralised with acetic acid.

Table 8.10 Determination of cyanide in plating waste waters by the isonicotinic acid-
barbituric acid method and the pyridine-pyrazolone method in comparison

CN − concentration (mg L −1 )

Sample

Isonicotinic acid-barbituric add method Pyridine- pyrazole method

2%
NaOH

2%
CH 3 COONa

2%
NaOH

2%
CH 3 COONa

I 0.04 0.04 0.03 0.04

II 0.11 0.12 0.10 0.12

III 0.19 0.18 0.19 0.18

IV 0.26 0.26

V 0.35 0.34 0.34 0.35

Source: Reproduced with permission from Gordon AC Breach [27]

Table 8.10 shows the good agreement in results for total cyanide obtained on wastewater
samples obtained by this method and by the spectrophotometric pyridine-pyrazolone
method [28].
Tan [29] also reported a spectrophotometric method for determining cyanide in
wastewater and non saline water using isonicotinic acid and barbituric acid as the colour-
forming system with an absorption maximum at 600nm. The method had a detection limit
of 0.6µg L −1 and recoveries >90%.
Another indirect spectrophotometric method for determining cyanide in wastewaters is
based on its reaction with the complex mercury(II)- tetrakis(4-triammoniumphenyl)-
porphyrin; decrease in the absorbance of the complex at 449nm is proportion to the
cyanide concentration [30]. In another study cyanide was reacted with copper(II) and
cetyltrimethylamine bromide to form a stable ternary complex which was extractable into
butanol and determined by atomic absorption spectrophotometry [31]. This method has a
detection limit of 3µg L −1 and the coefficient of variation was in the range of 1.77-
1.81%. Another spectrophotometric method for determining cyanide was based on its
reaction with bromine to form cyanogen bromide followed by reaction of the latter with
pyridine [32]. The gluconaldehyde so formed is coupled with phloroglucinol to form a
red violet dye, the absorbance of which is measured at 540nm. Beer's law was obeyed
over the range of 400-300µg L −1 .
The application of this technique is also discussed under multianion analysis in section